Most pupil are puzzled regarding the use of various salt-making methods.
(1) why can't titration be used for all the salts?
(2) Since the first reaction for the topic 'Acids-Bases' introduced 'acids react with REACTIVE metals to give salt and hydrogen gas, can we use this method instead?
Discussion:
There are many methods to make a salt, HOWEVER, we need to see if the method is feasible ( workable).
For the case of 'reactive metals and acids'
Of course, you can use reactive metals and acids to make a salt.
BUT, it will be too dangerous if you are using a REACTIVE metal.
Eg: To make Potassium chloride (KCl), it will be DANGEROUS if you are going to react Potassium with Hydrochloric acid ! Potassium explodes with cold water. [Can You Imagine the reaction of potassium with acids?]
Hence, this method ( acids with reactive metals) can only be used for metals that are moderately reactive! example: magnesium, zinc, etc.
If you want to form Copper(II) sulphate, you cannot use this method because copper is unreactive to acids!
Hence reacting copper(II) oxide/carbonate with acids is the ONLY method!
_____________________________________________________
For the case of 'insoluble oxides/insoluble carbonates with acids'
Ever wonder why it has to be insoluble reagents in the first place?
Back to basics: 'what are acids made of' ?
'An acid is a substance that produces H+ ions when dissolve in water.'
In short, there is water in an acid.
If the oxides and carbonates are soluble in water, then how do you ensure that your acids will be FULLY reacted?
remember in our procedure for heating insoluble oxides/carbonate with acids, step #2
(1) Warm the acid.
(2) add EXCESS insoluble oxides and carbonate and stir to dissolve.
(3) FILTER the mixture ........
If your acids did not REACT with the insoluble oxides/carbonate FULLY, then the acid will contaminate the salt that is formed in the process!
In short, for the usage of heating acids with reactive metals/ insoluble oxide/ insoluble carbonates, the REASONS behind it include:
(1) the oxides /carbonates will be insoluble in water, hence will definitely be able to react with the acids FULLY. Upon complete reaction with acids, all excess metal/insoluble oxides/carbonates will remained and this is an indication that all acids had fully reacted.
(2) the metals used are moderatly reactive and is suitable to react with warm acids.
______________________________________________________
What about 'titration'?
There are a few reasons for the usuage of titration.
The first reason is because the metal is too reactive and using their hydroxides is more appropriate.
Eg: to make sodium nitrate. We cannot use sodium metal as it is far too reactive with acids.
So, we use sodium HYDROXIDE and nitric acid.
In this case, we cannot use heating method as both are soluble and we cannot tell when neutralization takes place.
Hence, for the second reason:
Second reason: If you use soluble oxides and carbonates for the method of heating, one problem you foresee would be unable to know when neutralization occurs. Reason: all the reagents are soluble, you can't tell. ( recall for the case of heating insoluble oxides/carbonates, the reagent is insoluble so you can see when the reagent no longer dissolves in the acid).
But titration is able to tell because of the use of INDICATOR.
Hence, we will be able to know the EXACT amount of alkali needed to neutralize the acid to form the salt when the indicator CHANGES COLOUR.
Please do not state this reason as your answer for 'why titration is used': 'because if we use insoluble oxides/carbonates, it will not be able to pass through the burette' !!!!
I mentioned this point to the class because i wanted you to remember insoluble hydroxides and oxides cannot be used for titration in the LABORATORY. How can an insoluble reagent flow through a burette?
The answer why 'titration is used instead of heating method' because: ** both the reagents are soluble and there is NO INDICATION when neutralization takes place. For titration, indicator can be used to identify the point of neutralization.
Now, is it much clearer?!
Friday, January 16, 2009
2007 EYE PURE CHEM PAPER SOLUTION
SECTION A (MCQ)
1. (B)
2. (C)
3. Redox not covered in sec 3, anyway, answer is (A)
4. (A)
5. given no. of moles of Al2O3 = 1.0 mole
mole ratio of Al2O3:O2 is 2:3
no. of moles of oxygen is 3/2 x 1 = 1.5 moles
mass = mole x Mr of (O2)
= 1.5 x 2(16)
= 48 g (B)
6. chlorine = 2,8,7
when chlorine gains 1 electron to form chloride ion, it becomes 2,8,8 and it has 3 SHELLS
fluorine = 2,7
when fluorine gains 1 electron to form fluoride ion, it becomes 2,8 and it has 2 SHELLS
Magnesium = 2,8,2
when magnesium lose 2 electrons to form magnesium ion, it becomes 2,8 and it has 2 SHELLS
Oxygen = 2,6
when oxygen gains 2 electrons to form oxide ion, it becomes 2,8 and it has 2 SHELLS
so form the largest radius.... which means greater 'circumference' = chlorine
(A)
7. chemical analysis not tested in sec 3, anyway, answer is (B)
8. for graphite, each carbon atom is COVALENT bonded to each other. However, the carbon atoms form a HEXAGON RING. Each ring is connected to another ring by weak VAN DER WAALS ( weak VDW) forces of attraction. Graphite is used as lubricant because its layers can SLIDE over each other. (D)
9. (D)
All these elements are from group 2. All have 2 electrons in the outermost shell.
10. (B)
11. REDOX not teated in sec 3, anyway, answer is (D)
12. option (A) look like group 1 metals , option (B) look like macromolecules. copper is a metal, so it will have HIGH MP, HIGH DENSITY, GOOD ELECTRICAL CONDUCTIVITY (D)
13. (B)
14. empirical formula is the SIMPLEST ratio but MOLECULAR FORMULA is the formula multiply by a factor. In order to calculate the Molecular Formula, we need the relative molecular masses. Eg: the Mr of methane, CH4 is 16 while the Mr of (CH4 )2 is 32. (B)
3 a) ionic / ionic / covalent / covalent / covalent / covalent [2]
b) giant / giant / simple molecular [2]
c) MgO is ionic and giant structure is strong and stable, hence it has higher
melting point. whereas the SO3 is covalent bonding and a simple
molecular structure. [2]
d) Na2O(s) + H2O(l) ---> 2NaOH(aq) [1]
SO3(g) + H2O (l) ---> H2SO4(aq) [1]
4 ( chemical analysis not tested in sec 3 )
a) A Copper(II) carbonate [1]
B Carbon dioxide [1]
C Copper(II) chloride [1]
D Silver chloride [1]
E Copper(II) nitrate [1]
b) CuCO3 (s) + 2HCl(aq) ---> CuCl2(aq) +CO2(g)+ H2O(l)
CuCO3(s) + 2H+ ---> Cu2+(aq) +CO2(g)+ H2O(l) [2]
5 (oxidation and reduxtion not tested in sec 3)
a) i) +6 ii) +3 [2]
b) Aluminium [1]
c) gain of oxygen or increase in oxidation state [1]
d) Cr2O3 is oxidizing agent. [1]
6 a) i) yes, they all have similar formulae
ii) yes, peroxides and super oxides are likely formed at the
elements below the group.
b) O- , O2-
c) i) H+(aq) + OH-(aq) ---> H2O(l)
ii) 2I-(aq) + Cl2(g) ---> 2Cl-(aq) + I2(s)
iii) Zn(s) + 2H+(aq) ---> Zn2+(aq) + H2(g)
7 a) i. P6O4 ii. P3O2 [2]
b) It is an non-metal oxide
it is covalent bonding
it has no free electron and no mobile ions when molten. [3]
SECTION C (FREE RESPONSE)
1 a) i) Mg(s) + S(s) ---> MgS(s) [1]
iii) Mg :24 + S: 32 à MgS : 56
3 4
12g 16g
Actual: 16g of Mg is used, Sulphur will be used up first in the reaction. [1]
Hence sulphur is the limiting agent. [1]
iv) S MgS
32 56
16g 28g 28g of MgS formed [1]
b) CaCO3 (s) + H2SO4(aq) à CO2(g) + CaSO4(s) + H2O (l) [1]
100 24000
y 1200 [1]
y = 100 x 1200/ 24000
= 5 g (CaCO3 is reacted) [1]
Percentage purity = 5/6 x 100%
= 83.3 % [1]
2 a) i) % of Na = 12.5/45 x 100%
= 27.8%
ii) Na H C O
27.8 12. 14.3 56.7
27.8 1.2 14.3 56.7
23 1 12 16
1.2 1.2 1.19 3.54
1 1 1 3
Empirical formula = NaHCO3
iii) Mr of empirical formula (NaHCO3 )= 23+1+12+ 16x3 = 84
Mr of molecular of NaHCO3 =84
n = 84/84 = 1, Hence, molecular formula = NaHCO3 [1]
b) i) NaHCO3(aq) + HCl à NaCl (aq) + CO2(g) [1]
ii) 84 24
45 x
Conc. Of HCl = 91.3/36.5
= 2.5 mol/dm3
mol of HCl used = 280/1000 x 2.5
= 0.7 mol
hence, vol of CO2 produced = 0.7 x 24dm3
= 16.8 dm3
c) [ chemical analysis, not in syllabus ]
Add equal volume of sodium hydroxide and small spatula of
aluminium powder into a sample solution. [1]
Warm till the aluminium dissolves. [1]
Effervescence and pungent smell gas produced turns red litmus
paper blue. [1]
3 a) methyl orange [1]
b) 22.8 cm3 21.5 cm3 28.7 cm3 [1]
√ √ [1]
c) 25.0 cm3 [1]
d) H2SO4 + 2NaOH à Na2SO4 + 2H2O [1]
e) average of sulphuric acid used = (22.8 + 21.5) / 2 = 22.2 cm3 [1]
mol of H2SO4 / mol of NaOH = 1 / 2
mol of H2SO4 = ½ x mol of NaOH
0.05 x 22.2/1000 = ½ x 25/1000 x mol of NaOH
mol of NaOH = 0.0444 mol/dm3
Disclaimer: only the MCQ answers are from miss pang, answers from section B and C are done by another teacher. Miss Pang is not responsible for the accuracy of the answers!
1. (B)
2. (C)
3. Redox not covered in sec 3, anyway, answer is (A)
4. (A)
5. given no. of moles of Al2O3 = 1.0 mole
mole ratio of Al2O3:O2 is 2:3
no. of moles of oxygen is 3/2 x 1 = 1.5 moles
mass = mole x Mr of (O2)
= 1.5 x 2(16)
= 48 g (B)
6. chlorine = 2,8,7
when chlorine gains 1 electron to form chloride ion, it becomes 2,8,8 and it has 3 SHELLS
fluorine = 2,7
when fluorine gains 1 electron to form fluoride ion, it becomes 2,8 and it has 2 SHELLS
Magnesium = 2,8,2
when magnesium lose 2 electrons to form magnesium ion, it becomes 2,8 and it has 2 SHELLS
Oxygen = 2,6
when oxygen gains 2 electrons to form oxide ion, it becomes 2,8 and it has 2 SHELLS
so form the largest radius.... which means greater 'circumference' = chlorine
(A)
7. chemical analysis not tested in sec 3, anyway, answer is (B)
8. for graphite, each carbon atom is COVALENT bonded to each other. However, the carbon atoms form a HEXAGON RING. Each ring is connected to another ring by weak VAN DER WAALS ( weak VDW) forces of attraction. Graphite is used as lubricant because its layers can SLIDE over each other. (D)
9. (D)
All these elements are from group 2. All have 2 electrons in the outermost shell.
10. (B)
11. REDOX not teated in sec 3, anyway, answer is (D)
12. option (A) look like group 1 metals , option (B) look like macromolecules. copper is a metal, so it will have HIGH MP, HIGH DENSITY, GOOD ELECTRICAL CONDUCTIVITY (D)
13. (B)
14. empirical formula is the SIMPLEST ratio but MOLECULAR FORMULA is the formula multiply by a factor. In order to calculate the Molecular Formula, we need the relative molecular masses. Eg: the Mr of methane, CH4 is 16 while the Mr of (CH4 )2 is 32. (B)
15. given conc of acid = 1.0 M and mass of CaCO3 = 1.0 g.
no. of moles of CaCO3 = 1/100 = 0.01 mol
mole ratio of HCl: CaCO3 is 2:1
no. of moles of HCl = 0.01 x 2 = 0.02
vol = 0.02 / 1.0 = 0.02 dm3 = 20 cm3 (B)
16. H2SO4 + MgO ---> MgSO4 + H2O ;
H2SO4 + MgCO3 ---> MgSO4 + H2O + CO2
so, in both reactions, water is formed. (C)
17. CHEMICAL ANALYSIS not tested in sec 3, anyway, the answer is (A)
18. (A)
19. option B is very interesting. Covalent compounds are made up by atoms.... but the BETTER word for ' Nature of Particles' should be MOLECULES. Anyway, the formula for option B is wrong too. answer(C)
20. you need knowledge from Chemical Analysis, not tested in sec 3. Anyway, option (D)
21. (C)
22. if X is noble gas, then X,Y,Z is consecutive. So, Y should be in group 1, Z should be group 2.(D)
23. IMPT
Cl2 (g) + 2KBr ( aq) ---> 2KCl (aq) + Br2 (aq) ; colour of KBr and KCl = colourless; but aqueous Br2 = reddish brown
Cl2 (g) + 2KI (aq) ---> 2KCl (aq) + I2 (aq) ; colour of KI and KCl = colourless; but aqueous iodine is dark purple or blue (D)
24. although both potassium (2,8,1) and calcium (2,8, 2) have more electrons than aluminium ( 2,8,3 ). But aluminium donates MORE electrons into the sea : Al (s) ---> Al3+ (aq) + 3e- so answer (A)
25. total no. of electrons share = no. of BONDS in the molecule: 8 bonds x 2 e- = 16 e- answer (C)
26. (C) reason: the formula should be XO
27. when ammnium chloride is heated, it forms ammonia gas and hydrogen chloride gas: NH4Cl (s) ---> NH3 (g) + HCl (g) option (B)
28. notice the no. of protons and elecytrons for both X and Y is not equal! by right, in an neutral atom, X should have 4 electrons and 4 protons while Y should have 20 protons and 20 electrons. So this shows that both X and Y lose electrons. Only Metals lose electrons. Hence option (D)
29. R has 4 electrons involved in bonding. Hence R is in group 4. option (B)
30. given X contains acid ---> from universal indicator, X should have a pH less than 7. As for the reaction between KI and Pb(NO3)2, it will give a yellow ppt of PbI2 :
2 KI + Pb(NO3)2 ---> 2 KNO3 + PbI2 ( PbI2 is yellow ) option (A)
SECTION B (STRUCTURED )
1a) ammonia b) Chlorine
c) Lead (II) oxide
d) Magnesium chloride
e) Brass
2(a) chemical analysis Not tested in sec 3
a) zinc hydroxide / white / soluble in excess giving colourless solution. [1.5]
iron(II) hydroxide / dark green / insoluble in excess [1.5]
b) (i) Magnesium, sodium, caesium and beryllium [½]
(ii) Sodium, aluminium, magnesium and chlorine [½]
(iii) Hydrogen, sodium and caesium [½]
(iv) Carbon and tin [½]
3 a) ionic / ionic / covalent / covalent / covalent / covalent [2]
b) giant / giant / simple molecular [2]
c) MgO is ionic and giant structure is strong and stable, hence it has higher
melting point. whereas the SO3 is covalent bonding and a simple
molecular structure. [2]
d) Na2O(s) + H2O(l) ---> 2NaOH(aq) [1]
SO3(g) + H2O (l) ---> H2SO4(aq) [1]
4 ( chemical analysis not tested in sec 3 )
a) A Copper(II) carbonate [1]
B Carbon dioxide [1]
C Copper(II) chloride [1]
D Silver chloride [1]
E Copper(II) nitrate [1]
b) CuCO3 (s) + 2HCl(aq) ---> CuCl2(aq) +CO2(g)+ H2O(l)
CuCO3(s) + 2H+ ---> Cu2+(aq) +CO2(g)+ H2O(l) [2]
5 (oxidation and reduxtion not tested in sec 3)
a) i) +6 ii) +3 [2]
b) Aluminium [1]
c) gain of oxygen or increase in oxidation state [1]
d) Cr2O3 is oxidizing agent. [1]
6 a) i) yes, they all have similar formulae
ii) yes, peroxides and super oxides are likely formed at the
elements below the group.
b) O- , O2-
c) i) H+(aq) + OH-(aq) ---> H2O(l)
ii) 2I-(aq) + Cl2(g) ---> 2Cl-(aq) + I2(s)
iii) Zn(s) + 2H+(aq) ---> Zn2+(aq) + H2(g)
7 a) i. P6O4 ii. P3O2 [2]
b) It is an non-metal oxide
it is covalent bonding
it has no free electron and no mobile ions when molten. [3]
SECTION C (FREE RESPONSE)
1 a) i) Mg(s) + S(s) ---> MgS(s) [1]
iii) Mg :24 + S: 32 à MgS : 56
3 4
12g 16g
Actual: 16g of Mg is used, Sulphur will be used up first in the reaction. [1]
Hence sulphur is the limiting agent. [1]
iv) S MgS
32 56
16g 28g 28g of MgS formed [1]
b) CaCO3 (s) + H2SO4(aq) à CO2(g) + CaSO4(s) + H2O (l) [1]
100 24000
y 1200 [1]
y = 100 x 1200/ 24000
= 5 g (CaCO3 is reacted) [1]
Percentage purity = 5/6 x 100%
= 83.3 % [1]
2 a) i) % of Na = 12.5/45 x 100%
= 27.8%
ii) Na H C O
27.8 12. 14.3 56.7
27.8 1.2 14.3 56.7
23 1 12 16
1.2 1.2 1.19 3.54
1 1 1 3
Empirical formula = NaHCO3
iii) Mr of empirical formula (NaHCO3 )= 23+1+12+ 16x3 = 84
Mr of molecular of NaHCO3 =84
n = 84/84 = 1, Hence, molecular formula = NaHCO3 [1]
b) i) NaHCO3(aq) + HCl à NaCl (aq) + CO2(g) [1]
ii) 84 24
45 x
Conc. Of HCl = 91.3/36.5
= 2.5 mol/dm3
mol of HCl used = 280/1000 x 2.5
= 0.7 mol
hence, vol of CO2 produced = 0.7 x 24dm3
= 16.8 dm3
c) [ chemical analysis, not in syllabus ]
Add equal volume of sodium hydroxide and small spatula of
aluminium powder into a sample solution. [1]
Warm till the aluminium dissolves. [1]
Effervescence and pungent smell gas produced turns red litmus
paper blue. [1]
3 a) methyl orange [1]
b) 22.8 cm3 21.5 cm3 28.7 cm3 [1]
√ √ [1]
c) 25.0 cm3 [1]
d) H2SO4 + 2NaOH à Na2SO4 + 2H2O [1]
e) average of sulphuric acid used = (22.8 + 21.5) / 2 = 22.2 cm3 [1]
mol of H2SO4 / mol of NaOH = 1 / 2
mol of H2SO4 = ½ x mol of NaOH
0.05 x 22.2/1000 = ½ x 25/1000 x mol of NaOH
mol of NaOH = 0.0444 mol/dm3
Disclaimer: only the MCQ answers are from miss pang, answers from section B and C are done by another teacher. Miss Pang is not responsible for the accuracy of the answers!
Old Blog Revived!
Hey pupils,
I was so forgetful and I didnt remember my password and my poor blog was not manned.
I was so shocked that I noticed messages tagged on the C-Box that had vulgarities and profanities on it.
Please do not do such a thing, for if I want to pursue this issue, I can.
I welcome any of you to raise questions again!!!!
Sanny, you asked if you are not with me anymore, could you still ask me questions. Answer is YES!!!
Thank you Mr Chan for helping me to answer the questions . . . I really welcome you to visit the blog.
I was so forgetful and I didnt remember my password and my poor blog was not manned.
I was so shocked that I noticed messages tagged on the C-Box that had vulgarities and profanities on it.
Please do not do such a thing, for if I want to pursue this issue, I can.
I welcome any of you to raise questions again!!!!
Sanny, you asked if you are not with me anymore, could you still ask me questions. Answer is YES!!!
Thank you Mr Chan for helping me to answer the questions . . . I really welcome you to visit the blog.
Wednesday, July 2, 2008
The Chronicles Of 3 Little Pigs!
Another chronicle written by my sister.
Enjoy!
******************************************************************
The wolf which attacked the three little pigs had died from the fall off the chimney, but the story, or the chronicle of the 3 little pigs did not quite end there.
That fatal accident had created a huge stir-up and earned raved reports from the press. The proud wolves found that snub hard to stomach, and that incident had, to a certain extent, affected the operation of the local Bee Hiang Hiang store. Thanks-giving was round the corner, yet there was hardly any pig caught to serve as the main ingredient. The scarcity of pork made pessimists in the Wolf-Village turn to other food-alternatives, and many lived on a vegetarian diet.
This food crisis drove everyone in the Wolf-Village to desperation, and the wish for a sumptuous meal during the festive season brought the brains of Wolf-Village together, to stage a comeback. The review committee hired the well-learned Professor Wolff to conduct an independent review of that fatal accident. Analysis showed that the huff-puff method passed down from several generations before was obsolete and was no longer effective in toppling the brick houses built by the pigs. The R &D done by the pigs in Housing Development Authority (HDA) was indeed remarkable, and the suggestion made by Professor Wolff to solve this problem was to burn the brick house and force the pigs out of their sty.
He calculated that the brick house needed at least 100 000 kJ of energy to be completely engulf in fumes, and complete combustion of 1 mole of coal released approximately 100kJ of energy. The molecular mass of this special coal, coal W, designed by Professor Wolff, was 800.00g. Detailed calculations showed that 1000 mole of coal W was needed, which would weigh 6.023 x 10 23 x 800g x 1000 = 4.8184x10 29g.
As soon as the required amount of coal W was produced, everyone from the Wolf Village was mobilized to transport the coal. The Huff-Puff method was abandoned, but the transportation left everyone huffing and puffing. The target sty for the first attack to be launched was the sty built by the 3 little pigs who were responsible the many months of distress suffered by villagers in the Wolf Village.
It was by no means an accident that the 3 little pigs survived. Although the previous ordeal was a victory for them, they did not rest on their laurels but worked on improving the safety aspects of their estate. They knew that although their houses were “huff-puff-proof”, they were nevertheless not fire-proof and would engulf in flames should a fire break out.
The smart 3 little pigs had long designed a hot air balloon that could support the mass of the 3 of them should there be a fire. Careful calculations and experimentation showed that in order for the hot air balloon to support their weight as well as the necessary amount of coal for continual burning, 2400dm3 per second of hot air was needed. One mole of a specially-designed, fuel efficient coal, coal P could provide 1 mole of hot air, which is 24dm3 upon combustion.
Thus in order for the 3 of them to stay in the air for 1 hour, 60 x 60 x 100 = 360000 mole of coal P was necessary. The molecular mass of coal P is 600.00g. Thus the total mass of coal P required was 600 x 360000 = 216000000g. Wow!!!
The time was ripe when Professor Wolff saw strong wind blowing in the direction of Pansy Village, the village where the 3 little pigs stayed.
“Comrades! Start the fire! ” ordered Professor Wolff, as he sat a distance away from that brick house, sipping red wine, waiting for succulent pork to be served soon. Professor Wolff choked on his drink when he saw the roof of the brick house shoot-open, and the 3 little pigs flying-off with a smirk on their face in the hot air balloon! The sudden attack had failed to restore the reputation of the wolves being the most-capable animals in PW town (consisting of only Pansy and Wolf Village), but further undermines the standing of Wolf Village in PW town. My goodness!!!
It appeared that the coming Thanks Giving dinner in Wolf Village had no choice but to serve many salad dishes, and there was a real prospect that a vegetarian diet might stay for good.
by: xue yin ( another miss pang )
Enjoy!
******************************************************************
The wolf which attacked the three little pigs had died from the fall off the chimney, but the story, or the chronicle of the 3 little pigs did not quite end there.
That fatal accident had created a huge stir-up and earned raved reports from the press. The proud wolves found that snub hard to stomach, and that incident had, to a certain extent, affected the operation of the local Bee Hiang Hiang store. Thanks-giving was round the corner, yet there was hardly any pig caught to serve as the main ingredient. The scarcity of pork made pessimists in the Wolf-Village turn to other food-alternatives, and many lived on a vegetarian diet.
This food crisis drove everyone in the Wolf-Village to desperation, and the wish for a sumptuous meal during the festive season brought the brains of Wolf-Village together, to stage a comeback. The review committee hired the well-learned Professor Wolff to conduct an independent review of that fatal accident. Analysis showed that the huff-puff method passed down from several generations before was obsolete and was no longer effective in toppling the brick houses built by the pigs. The R &D done by the pigs in Housing Development Authority (HDA) was indeed remarkable, and the suggestion made by Professor Wolff to solve this problem was to burn the brick house and force the pigs out of their sty.
He calculated that the brick house needed at least 100 000 kJ of energy to be completely engulf in fumes, and complete combustion of 1 mole of coal released approximately 100kJ of energy. The molecular mass of this special coal, coal W, designed by Professor Wolff, was 800.00g. Detailed calculations showed that 1000 mole of coal W was needed, which would weigh 6.023 x 10 23 x 800g x 1000 = 4.8184x10 29g.
As soon as the required amount of coal W was produced, everyone from the Wolf Village was mobilized to transport the coal. The Huff-Puff method was abandoned, but the transportation left everyone huffing and puffing. The target sty for the first attack to be launched was the sty built by the 3 little pigs who were responsible the many months of distress suffered by villagers in the Wolf Village.
It was by no means an accident that the 3 little pigs survived. Although the previous ordeal was a victory for them, they did not rest on their laurels but worked on improving the safety aspects of their estate. They knew that although their houses were “huff-puff-proof”, they were nevertheless not fire-proof and would engulf in flames should a fire break out.
The smart 3 little pigs had long designed a hot air balloon that could support the mass of the 3 of them should there be a fire. Careful calculations and experimentation showed that in order for the hot air balloon to support their weight as well as the necessary amount of coal for continual burning, 2400dm3 per second of hot air was needed. One mole of a specially-designed, fuel efficient coal, coal P could provide 1 mole of hot air, which is 24dm3 upon combustion.
Thus in order for the 3 of them to stay in the air for 1 hour, 60 x 60 x 100 = 360000 mole of coal P was necessary. The molecular mass of coal P is 600.00g. Thus the total mass of coal P required was 600 x 360000 = 216000000g. Wow!!!
The time was ripe when Professor Wolff saw strong wind blowing in the direction of Pansy Village, the village where the 3 little pigs stayed.
“Comrades! Start the fire! ” ordered Professor Wolff, as he sat a distance away from that brick house, sipping red wine, waiting for succulent pork to be served soon. Professor Wolff choked on his drink when he saw the roof of the brick house shoot-open, and the 3 little pigs flying-off with a smirk on their face in the hot air balloon! The sudden attack had failed to restore the reputation of the wolves being the most-capable animals in PW town (consisting of only Pansy and Wolf Village), but further undermines the standing of Wolf Village in PW town. My goodness!!!
It appeared that the coming Thanks Giving dinner in Wolf Village had no choice but to serve many salad dishes, and there was a real prospect that a vegetarian diet might stay for good.
by: xue yin ( another miss pang )
My sister and shana inspired me ( not shana's fault, so please don't blame her ) to offer one of my chem classes on a written assignment ' The Chronicles Of The Mole '.
Being a weak english person, I try my best to write an event regarding the mole.
Enjoy...
*******************************************************
Huai Ren was waiting outside the A & E. The police had notified him of Jenny’s accident.
After the operation, he was informed by the surgeon that Jenny had escaped death and would be transferred to intensive care unit.
Huai Ren entered the room. Accordingly, Jenny had sprained her neck and fractured her ribs due to the crash. The fractured ribs pierced through bronchiole and the doctor had to give her pain killers through injections. Jenny’s arms suffered from deep cuts due to the broken windscreen.
Huai Ren walked towards Jenny and lamented at her misfortunes.
She was not like this before, at least 1 year ago.
Jenny had suffered from post natal syndrome ; after her maternity leave, she needed to deal with the day-to-day operations of the company and these had proven too much for her. Her dad had suggested Huai Ren to take over the CEO position so as to lessen her duties. Recently, the company was faced with problems of cash flow. A large sum of funds was trapped in an acquisition project of a promising company’s shares.
Jenny insisted Huai Ren had misappropriated the company’s funds.
Huai Ren left the ward for he knew if she woke up, he would not be the person Jenny would want to see.
After visiting hours, someone entered Jenny’s ward.
He took out a syringe and held Jenny’s arm. With a swift movement, the hollow needle pierced through the skin and into the vein. 2.25mg/dm3 of Warfarin was injected into the bloodstream via the vein. He had done his calculations well. For every 13 kg of body weight, there is an equivalent amount of 1 litres of blood. So, Jenny would have around 4 litres of blood if she weighed 50 kg.
The maximum concentration of warfarin that her body could take should not exceed 5.0 mg per body of blood. Since concentration can be defined as amount of substance dissolved in 1 L, which is 5.0/ 4 = 1.25 mg/dm3. An overdose of warfarin will lead to bleed profusely as blood will not clot.
He could visualise the shock on the nurses’ faces when they saw her bleeding while doing their rounds the next morning. Blood would be oozing non stop from her cuts.
*******************************************************
ms pang:)
Being a weak english person, I try my best to write an event regarding the mole.
Enjoy...
*******************************************************
Huai Ren was waiting outside the A & E. The police had notified him of Jenny’s accident.
After the operation, he was informed by the surgeon that Jenny had escaped death and would be transferred to intensive care unit.
Huai Ren entered the room. Accordingly, Jenny had sprained her neck and fractured her ribs due to the crash. The fractured ribs pierced through bronchiole and the doctor had to give her pain killers through injections. Jenny’s arms suffered from deep cuts due to the broken windscreen.
Huai Ren walked towards Jenny and lamented at her misfortunes.
She was not like this before, at least 1 year ago.
Jenny had suffered from post natal syndrome ; after her maternity leave, she needed to deal with the day-to-day operations of the company and these had proven too much for her. Her dad had suggested Huai Ren to take over the CEO position so as to lessen her duties. Recently, the company was faced with problems of cash flow. A large sum of funds was trapped in an acquisition project of a promising company’s shares.
Jenny insisted Huai Ren had misappropriated the company’s funds.
Huai Ren left the ward for he knew if she woke up, he would not be the person Jenny would want to see.
After visiting hours, someone entered Jenny’s ward.
He took out a syringe and held Jenny’s arm. With a swift movement, the hollow needle pierced through the skin and into the vein. 2.25mg/dm3 of Warfarin was injected into the bloodstream via the vein. He had done his calculations well. For every 13 kg of body weight, there is an equivalent amount of 1 litres of blood. So, Jenny would have around 4 litres of blood if she weighed 50 kg.
The maximum concentration of warfarin that her body could take should not exceed 5.0 mg per body of blood. Since concentration can be defined as amount of substance dissolved in 1 L, which is 5.0/ 4 = 1.25 mg/dm3. An overdose of warfarin will lead to bleed profusely as blood will not clot.
He could visualise the shock on the nurses’ faces when they saw her bleeding while doing their rounds the next morning. Blood would be oozing non stop from her cuts.
*******************************************************
ms pang:)
Thursday, June 19, 2008
2005 SciChemistry MCQ
2005 MCQ
1) A * explanation *less dense means light, so we use the upward dispalcement method( see notes blog )
so, reject option B. B is for heavy gases ( downward displacement method )
option C is for insoluble gases.
2) C
* explanation *
when particles at 50'C ( liquid ) becomes 120'C ( gases ),the energy of the particles increases, the spacing between the particles becomes far apart and hence the attractive forces between the particles decreases.
3) C* explanation *81 is nucleon number ( proton + neutrons ) / atomic mass37 is proton number ( proton = electron )therefore, 81-37= 44 neutrons.
4) C* explanation *Element X has a valency of +1Element Y has a valency of -2
therefore, when you use the criss-cross method, the formula is X2Y1
5) D
* explanation *look at what is given to you: you have 0.3 moles of C3H8.to find volume of gaseous productsso, which is the product they want? from the question, there is CO2 and H2O?answer: look at the state symbols, CO2 is in (g) state!!!mole ratio of C3H8 : CO2 is 1: 3no. of moles ofC3H8 = 0.1,1unit = 0.1,3 units = 0.1X 3 = 0.3 moles(please dont be careless and choose option B!! we have only found CO2's mole, the question wants VOLUME ) so,using P.K.X fav sentence: 1 mole of any gas = 24 dm3 at r.t.p,so, 0.3 mole = 0.3 X 24 = 7.2 dm3
7) B
* explanation *
during the process of neutralization, the temperature will increase ( see notes blog )that is why options C and D are out!now, when neutralization finishes, the ecess alkali added will make the temperature of the solution back to room temperature. Hence a decreasing gradient.
8) B
option A: when a more concentrated acid is used, the gradient of the graph will be steeper instead of gentle because the rate of reaction is faster.option C: when fewer amounts of reactant is used, the amount of CO2 produced will be less. So, it will not reached the same level as graph 1.option D: when powdered reactant is used, speed of reaction should increase, instead of decrease!
9) B
* explanation *
option A, D are out because all potassium salts are soluble!
12) D
* explanation *option A: coke is not used to oxidised slag!! coke is used to burn to give carbon dioxide and carbon monoxide!
20) D* explanation *polyester = many units of ester group.
Terylene contains ester linkage.Nylon contains amide linkage.Poly(ethene) contains many units of ethene .Protein contains amide linkage.
1) A * explanation *less dense means light, so we use the upward dispalcement method( see notes blog )
so, reject option B. B is for heavy gases ( downward displacement method )
option C is for insoluble gases.
2) C
* explanation *
when particles at 50'C ( liquid ) becomes 120'C ( gases ),the energy of the particles increases, the spacing between the particles becomes far apart and hence the attractive forces between the particles decreases.
3) C* explanation *81 is nucleon number ( proton + neutrons ) / atomic mass37 is proton number ( proton = electron )therefore, 81-37= 44 neutrons.
4) C* explanation *Element X has a valency of +1Element Y has a valency of -2
therefore, when you use the criss-cross method, the formula is X2Y1
5) D
* explanation *
Element Q has 4 valence electrons
---> group 4 ( since number of valece electrons = group number )
Hydrogen and chlorine are non-metals.
So, non-metal & non-metal = covalent compound.
properties of covalent compound = low melting point ( see notes blog )
6) D
* explanation *look at what is given to you: you have 0.3 moles of C3H8.to find volume of gaseous productsso, which is the product they want? from the question, there is CO2 and H2O?answer: look at the state symbols, CO2 is in (g) state!!!mole ratio of C3H8 : CO2 is 1: 3no. of moles ofC3H8 = 0.1,1unit = 0.1,3 units = 0.1X 3 = 0.3 moles(please dont be careless and choose option B!! we have only found CO2's mole, the question wants VOLUME ) so,using P.K.X fav sentence: 1 mole of any gas = 24 dm3 at r.t.p,so, 0.3 mole = 0.3 X 24 = 7.2 dm3
7) B
* explanation *
during the process of neutralization, the temperature will increase ( see notes blog )that is why options C and D are out!now, when neutralization finishes, the ecess alkali added will make the temperature of the solution back to room temperature. Hence a decreasing gradient.
8) B
option A: when a more concentrated acid is used, the gradient of the graph will be steeper instead of gentle because the rate of reaction is faster.option C: when fewer amounts of reactant is used, the amount of CO2 produced will be less. So, it will not reached the same level as graph 1.option D: when powdered reactant is used, speed of reaction should increase, instead of decrease!
9) B
* explanation *
option A, D are out because all potassium salts are soluble!
remember the K-N-N-Na theory.
option C is out. Potassium sulphate is a salt, not a base.
answer is potassium carbonate neutralises the acid.
10) C
* explanation *
when halogen is Y added to X and Z, there is no reaction, this means that Y is the least reactive.
so, down the group of 7, reactivity decreases, so, Br- is the least reactive.
so, Y = Br-
if X can displace Y and Z, then X is the most reactive.
so, X = Cl-
11) B
12) D
* explanation *option A: coke is not used to oxidised slag!! coke is used to burn to give carbon dioxide and carbon monoxide!
option B: limestone is used to decomposed to form calcium oxide and carbon dioxide.
the calcium oxide is used to neutralise slag.
option C: molten iron is heavier, so it is at the bottom, and not floats on the slag!
13) D
14) B
15) A ( see textbook for the uses of cracking )
16) A
* explanantion *
in the complete combustion of organic compounds, only carbon dioxide and water are formed.
17) D
18) C
* explanation *
only compounds with C=C bonds will decolourise aqueous brmine.
other C= structure will not decompose aqueous bromine.
19) C ( see textbook )
20) D* explanation *polyester = many units of ester group.
Terylene contains ester linkage.Nylon contains amide linkage.Poly(ethene) contains many units of ethene .Protein contains amide linkage.
Saturday, June 14, 2008
Remedial Timeslots for 3E2 Pure Chemistry
Dear 3E2,
These are the timeslots for our InTeNsIvE TrAiNiNg PrOgRaMmE.
Please bring your stationaries, Five Year Series and Chemistry Textbook and File.
Venue: 3E2 classroom
16/06/08
Elements, Mixture and Compounds
Time: 11.15am to 12.45 pm
17/06/08
Structure of solids, Bonding
Time: 9am to 12 pm
18/06/08
Balancing Equations
Time: 2pm to 4 pm
Note:
I am having lessons for 4a,4e and 5a on 16th and 18th, so i cannot schedule your 'programme' eariler.
The lesson will end early if we finish our planned programme. Please do not be late for lessons.
miss pang :)
These are the timeslots for our InTeNsIvE TrAiNiNg PrOgRaMmE.
Please bring your stationaries, Five Year Series and Chemistry Textbook and File.
Venue: 3E2 classroom
16/06/08
Elements, Mixture and Compounds
Time: 11.15am to 12.45 pm
17/06/08
Structure of solids, Bonding
Time: 9am to 12 pm
18/06/08
Balancing Equations
Time: 2pm to 4 pm
Note:
I am having lessons for 4a,4e and 5a on 16th and 18th, so i cannot schedule your 'programme' eariler.
The lesson will end early if we finish our planned programme. Please do not be late for lessons.
miss pang :)
Sunday, June 8, 2008
Reply to Germaine's Question : Is hydrogen a metal or non-metal
GERMAINE: hydrogen is metal or non metal?
My Reply: Hydrogen is a non-metal! However, it loses electrons to form H+ ions. ( so, i guess that is why Germaine will question its identity ).
The reason is it is more stable.
However, in tertiary levels ( JCs / Polys/Uni ), Hydrogen can also gain electrons, which is H- ions ( hydride ). There exist many metal compounds in which metal bonds with hydrogen and hydrogen gains ELECTRONS from metals. Such compounds are known as Metal Hydrides!
Thankfully, not in your syllabus!
ms pang :)
My Reply: Hydrogen is a non-metal! However, it loses electrons to form H+ ions. ( so, i guess that is why Germaine will question its identity ).
The reason is it is more stable.
However, in tertiary levels ( JCs / Polys/Uni ), Hydrogen can also gain electrons, which is H- ions ( hydride ). There exist many metal compounds in which metal bonds with hydrogen and hydrogen gains ELECTRONS from metals. Such compounds are known as Metal Hydrides!
Thankfully, not in your syllabus!
ms pang :)
Reply to Mark's Question
Mark asked: ' i thought carbon-carbon is a quadriplet bond? and is in diamond, which is a giant colvent bonding. '
My reply to HJ's question was ' Are there any COMPOUNDS with carbon - carbon quadruple bond. '
Your comment was for diamond.
Firstly, diamond is made up by many many CARBON atoms joined together through covalent bonding. It DOES NOT have any other elements ( only carbon atoms ) in the composition of diamond. So, it is not the same as HJ's question as diamond is an element, not a compound.
Secondly, Quadruple bonds means one element shares 4 electrons with another element, and vice versa. Total 8 electrons within the 4 bonds.
For diamond, each carbon atom forms only one bond with another carbon atom. Which means each carbon atom forms 4 single bonds with 4 other carbon atoms!
ms pang:)
p/s: I am not taking a break.... was busy with the preparation for philippine's trip!
My reply to HJ's question was ' Are there any COMPOUNDS with carbon - carbon quadruple bond. '
Your comment was for diamond.
Firstly, diamond is made up by many many CARBON atoms joined together through covalent bonding. It DOES NOT have any other elements ( only carbon atoms ) in the composition of diamond. So, it is not the same as HJ's question as diamond is an element, not a compound.
Secondly, Quadruple bonds means one element shares 4 electrons with another element, and vice versa. Total 8 electrons within the 4 bonds.
For diamond, each carbon atom forms only one bond with another carbon atom. Which means each carbon atom forms 4 single bonds with 4 other carbon atoms!
ms pang:)
p/s: I am not taking a break.... was busy with the preparation for philippine's trip!
Wednesday, April 23, 2008
Reply to HJ's Question: Are there any compounds with quadriplet bond?
Hj: ms pang,is there such thing as quadriplet bond?
my reply: Should not have at your level. The maximum number of bonds between two atoms is only triple bond. eg:
my reply: Should not have at your level. The maximum number of bonds between two atoms is only triple bond. eg:
dot and cross structure of nitrogen molecule
Structural formula ( read as ' N triple bond N ' )
As for the presences of quadruple bond... yes.... mainly in transition metal. Eg: Chromium.
I double check with miss wendy heng regarding HJ's question and I almost forgotten that in uni, we did manage to draw quadruple bond!!! ( many thanks to her ).
Just for your information... not in your secondary syllabus.....
chromium acetate
I edited this diagram so that you can see the quadruple bond easier... the original diagram is blur and show 5 bonds due to low resolutions.
I didnt draw these structures, i got it from this website:
(1) http://www.gcsescience.com/a25.htm ( nirogen molecule )
(2) wwwchem.uwimona.edu.jm:1104/courses/chromium.html ( chromium acetate )
p/s: is KING = Gareth? .. i assume HJ as 'hong jie'
ms pang :)
Saturday, April 19, 2008
Chemistry Remedial For 4E1/4 Sci-Chemistry and 3E2 Pure Chemistry
Dear 4E1/4 and 3E2
In view of the upcoming MYE ( mid year exam )2008. There will be remedials for these days:
4E1/4 ( 3e2, be patient. Your timeslot is written below 4E .. so read on)
Our remedial will resumes from this saturday ( 26 april 08 ) onwards. Reason for cancelling the remedial on 19 april is due to real busy day of mine from morning.
The remedial will be conducted at only 1 slot: 10 am till 11.30am at AVA.
Target audience... 60 pax of you.
Topic: Chemical Analysis ( Cation/Anion)
This is a SUPER difficult and important topic ; this topic worths at least [5 mks ] in exam EVER YEAR without fail.
Since this topic needs alot of practice... we will continue with more practise for chemical analysis on 3 May 08. Same time, same venue.
You are advise to turn up for both sessions so you can have maximum exposure to this topic. Should you choose to attend only 1 of the above sessions, you may feel lost as practise is a continuation process.
3E2
Please inform your parents you have remedial.
Session 1- Revision: Structure of Atoms & Bonding ( 26 april 08 / 8.30-9.30/AVA )
Session 2- Revision: Formulas & Balancing Equation ( 3 may 08 / 8.30-9.30/AVA )
I will be going through FYS on 30 April. So all of you please stay back after your last paper. Have your lunch before our revision.
For administration purpose and monitoring of results, these are the pupils who attend sat remedial:
22 march 08
anas, michael, jason, yazid, cheryl, natasha, cheng hong, ronald
29 march 08
jessica, weifen, jolene, farid, anas, michael, jason, cheng hong, natasha, cheryl, jeffery
05 march 08
farid, jeffery, cheng hong, david, michael, anas, meiling, jolene, natasha, cheryl, jia min, yan ne, pei yee, weifen
__________________________________________________
The preparation for O-Level Exam is similarly to preparing for a Marathon.....
Before you run, you need to warm up. However, with 'conditioning your body' for the run, it is impossible to have a marathon because it may lead to sprains and you may not even complete the run!!!
Slow and steady wins the race.
cheers,
ms pang:)
In view of the upcoming MYE ( mid year exam )2008. There will be remedials for these days:
4E1/4 ( 3e2, be patient. Your timeslot is written below 4E .. so read on)
Our remedial will resumes from this saturday ( 26 april 08 ) onwards. Reason for cancelling the remedial on 19 april is due to real busy day of mine from morning.
The remedial will be conducted at only 1 slot: 10 am till 11.30am at AVA.
Target audience... 60 pax of you.
Topic: Chemical Analysis ( Cation/Anion)
This is a SUPER difficult and important topic ; this topic worths at least [5 mks ] in exam EVER YEAR without fail.
Since this topic needs alot of practice... we will continue with more practise for chemical analysis on 3 May 08. Same time, same venue.
You are advise to turn up for both sessions so you can have maximum exposure to this topic. Should you choose to attend only 1 of the above sessions, you may feel lost as practise is a continuation process.
3E2
Please inform your parents you have remedial.
Session 1- Revision: Structure of Atoms & Bonding ( 26 april 08 / 8.30-9.30/AVA )
Session 2- Revision: Formulas & Balancing Equation ( 3 may 08 / 8.30-9.30/AVA )
I will be going through FYS on 30 April. So all of you please stay back after your last paper. Have your lunch before our revision.
For administration purpose and monitoring of results, these are the pupils who attend sat remedial:
22 march 08
anas, michael, jason, yazid, cheryl, natasha, cheng hong, ronald
29 march 08
jessica, weifen, jolene, farid, anas, michael, jason, cheng hong, natasha, cheryl, jeffery
05 march 08
farid, jeffery, cheng hong, david, michael, anas, meiling, jolene, natasha, cheryl, jia min, yan ne, pei yee, weifen
__________________________________________________
The preparation for O-Level Exam is similarly to preparing for a Marathon.....
Before you run, you need to warm up. However, with 'conditioning your body' for the run, it is impossible to have a marathon because it may lead to sprains and you may not even complete the run!!!
Slow and steady wins the race.
cheers,
ms pang:)
Tuesday, April 15, 2008
Reply To Mark's Question: Why must we have UV light for free radical substitution.
My reply:
Firstly to have chlorine radical, i need to get it from chlorine molecule....
So, I need a minimum energy to break up my chlorine molecule to get chlorine radical....
ms pang :)
Firstly to have chlorine radical, i need to get it from chlorine molecule....
So, I need a minimum energy to break up my chlorine molecule to get chlorine radical....
ms pang :)
Reply To Mark's Question: Nobel Gases Group 8 or Group 18
Mark asked: ms pang, why is it we learn that nobel gas are grp 8 metals when they are grup 18? source: http://en.wikipedia.org/wiki/Noble_gases
my reply:
Indeed an interesting question!!!
But, let me make an amendment to your question...
Noble Gases are group X or group 0 non-metals.... not METALS.
Anyway, why wikipedia says group 18?
This is a new TERMINOLOGY....
Most scientist wanted to fit Transitions Metal into groups too... recall in our periodic table, transition metals are catagorise as a 'rectangular block' with no group......
So, after adding the transitions metal, we will have 18 groups hence noble gases become group 18!!!
Nonetheless, facts from websites cannot be trusted wholesomely..... unless it is some education (edu) or government (gov) websites..... such websites have more credibility.
ms pang :)
my reply:
Indeed an interesting question!!!
But, let me make an amendment to your question...
Noble Gases are group X or group 0 non-metals.... not METALS.
Anyway, why wikipedia says group 18?
This is a new TERMINOLOGY....
Most scientist wanted to fit Transitions Metal into groups too... recall in our periodic table, transition metals are catagorise as a 'rectangular block' with no group......
So, after adding the transitions metal, we will have 18 groups hence noble gases become group 18!!!
Nonetheless, facts from websites cannot be trusted wholesomely..... unless it is some education (edu) or government (gov) websites..... such websites have more credibility.
ms pang :)
Reply To Hao Eng's Question: Does SO2 have double bonds?
Hao Eng asked: Does SO2 have double bonds between them?
My reply: Yes!
Both sulphur and oxygen has 6 electrons in their outermost shell. In order to have 8 electrons for oxygen atoms (octet structure ), sulphur needs to share 2 electrons with EACH oxygen.
Alas, then sulphur will have 10 electrons!!! Which is not octet structure!
In tertiary levels ( jc/poly/uni), sulphur can 'expand octet' which is a term refering to an atom that has more than 8 electrons in its outermost shell ...
A piece of good news. You are not expected to draw this structure for O-level Exam.....
ms pang :)
p/s: i didnt draw this diagram, i got it from this website:
http://www.btinternet.com/~chemistry.diagrams/molecular_diagrams.htm
Reply To Qi Ying's Question: How many bonds does chlorine and hydrogen have?
Qi Ying asked: how many bonds does chlorine and hydrogen have?
my reply:
Chlorine and hydrogen does not have bonds. The question 'should be' how many electrons can the hydrogen and chlorine used for bonding.
Chlorine is in Group 7 so it has 7 electrons.
If it combines with a metal group, then it can only accept 1 electron from the metal. ( so that add up to be 8 electrons )
If it combines with a non-metal group, then it can share only 1 electron from the non-metal thus forming 8 electrons too.
In this case, if chlorine combines with hydrogen to form hydrogen chloride, then only 1 bond is formed between hydrogen and chlorine.
ms pang :)
my reply:
Chlorine and hydrogen does not have bonds. The question 'should be' how many electrons can the hydrogen and chlorine used for bonding.
Chlorine is in Group 7 so it has 7 electrons.
If it combines with a metal group, then it can only accept 1 electron from the metal. ( so that add up to be 8 electrons )
If it combines with a non-metal group, then it can share only 1 electron from the non-metal thus forming 8 electrons too.
In this case, if chlorine combines with hydrogen to form hydrogen chloride, then only 1 bond is formed between hydrogen and chlorine.
ms pang :)
Tuesday, March 4, 2008
Groupings for March Holiday's Project
Dear all,
please double check your grouping,
Group 1: Ionic compound (NaCl, MgCl2)
Gareth
Mikhail
Chong cheng
Hong jie
Naufal
Group 2: Ionic Compound (NaF, CaCl2)
Jeremy
Yan seng
Nadi
Jovin
Group 3: Simple covalent molecules (H2O, CO2,CH4, O2,H2,Cl2, HCl, NH3, CO, C2H4)
June
Qian hui
Eileen
Bao yuan
Jun ling
Group 4: Simple covalent molecules (H2O,CO2,CH4,O2,H2,Cl2, HCl, SO2, CH3COOH)
Shi min
Candi
Fiona
Qi ying
Hao eng
Group 5: Macromolecules (diamond, graphite)
Jerry
Hung yih
Zi jun
Jian Qiang
Kevin
Group 6: Macromolecules (silicon dioxide, graphite)
nil
attention to shana, nicole, zhi ying, shermaine, celin and sheng lin you girls have not sign up for your topic!!!
please double check your grouping,
Group 1: Ionic compound (NaCl, MgCl2)
Gareth
Mikhail
Chong cheng
Hong jie
Naufal
Group 2: Ionic Compound (NaF, CaCl2)
Jeremy
Yan seng
Nadi
Jovin
Group 3: Simple covalent molecules (H2O, CO2,CH4, O2,H2,Cl2, HCl, NH3, CO, C2H4)
June
Qian hui
Eileen
Bao yuan
Jun ling
Group 4: Simple covalent molecules (H2O,CO2,CH4,O2,H2,Cl2, HCl, SO2, CH3COOH)
Shi min
Candi
Fiona
Qi ying
Hao eng
Group 5: Macromolecules (diamond, graphite)
Jerry
Hung yih
Zi jun
Jian Qiang
Kevin
Group 6: Macromolecules (silicon dioxide, graphite)
nil
attention to shana, nicole, zhi ying, shermaine, celin and sheng lin you girls have not sign up for your topic!!!
Sunday, February 17, 2008
Reply To Mark's Question: Is there such a substance CaClOH?
Mark asked: 'just to check, is there such thing as CaClOH ?'
My reply: Yes!!!! But not in your syllabus.
In the reaction of HCl and limestone under furnace and boiler conditions, CaClOH is an INTERMEDIATE product.
'intermediate product' means, the reaction produce this product and this product (known as intermediate product) will further react or continue in the reaction to form the final product.
If not, under NORMAL conditions, HCl will react with CaCO3 ( limestone) to form carbon dioxide, calcium chloride and water.
ms pang:)
My reply: Yes!!!! But not in your syllabus.
In the reaction of HCl and limestone under furnace and boiler conditions, CaClOH is an INTERMEDIATE product.
'intermediate product' means, the reaction produce this product and this product (known as intermediate product) will further react or continue in the reaction to form the final product.
If not, under NORMAL conditions, HCl will react with CaCO3 ( limestone) to form carbon dioxide, calcium chloride and water.
ms pang:)
Saturday, February 16, 2008
Saturday Revision Topics: Group Properties
Dear all,
Some of you are not required to attend the saturday's remedial due to your better chemistry results. You may get a copy of the extra exercises ( 1st remedial- mole concept; 2nd remedial: Group Properties) from me every week on monday!
However, answers are not provided. Please complete on your own before seeking Mrs Jaya or myself for help.
As for the pupils who have been attending the remedials regularly, please continue to do so.
It is easier to revise and complete the exercises with help rather than struggling to complete it on your own! In addition, you can clarify your doubts!
Apologies for the cancellation of 2 slots due to my revision for 3A3 today.
The attendance is as follows:
Michael, Yazid, Cheryl and Natasha ( 10-11am)
Cheng Hong, Yanne, Acslyn [ i spelt correctly:) ], Geok Teng ( 11-12pm)
Some of you are not required to attend the saturday's remedial due to your better chemistry results. You may get a copy of the extra exercises ( 1st remedial- mole concept; 2nd remedial: Group Properties) from me every week on monday!
However, answers are not provided. Please complete on your own before seeking Mrs Jaya or myself for help.
As for the pupils who have been attending the remedials regularly, please continue to do so.
It is easier to revise and complete the exercises with help rather than struggling to complete it on your own! In addition, you can clarify your doubts!
Apologies for the cancellation of 2 slots due to my revision for 3A3 today.
The attendance is as follows:
Michael, Yazid, Cheryl and Natasha ( 10-11am)
Cheng Hong, Yanne, Acslyn [ i spelt correctly:) ], Geok Teng ( 11-12pm)
Amendment To 4E1/4E4 Science Chemistry Common Test Topics
Dear 4E1/4E4,
There are a total of 5 topics for your common test on 20th feb.
The topics are:
(1) Chemical Bonding
(2) Mole concept
(3) Periodic Table and Group Properties
(4) Metals
(5) Redox ( reduction and oxidation )
Sorry for the amendment :(
There are a total of 5 topics for your common test on 20th feb.
The topics are:
(1) Chemical Bonding
(2) Mole concept
(3) Periodic Table and Group Properties
(4) Metals
(5) Redox ( reduction and oxidation )
Sorry for the amendment :(
Saturday, February 9, 2008
Time slots for next saturday remedial 16 Feb 2008
Dear 4E1/4E4 pupils,
Attendance is COMPLUSORY for pupils who failed the metal test or the mole concept test!!
i will be revising metals (especially displacement reactions) and simple redox ( reduction and oxidation ) on 16 Feb.
These are the time slots:
(1) 8.30 am-9.30 am
(2) 9.45 am-10.45 am
(3) 11.oo am- 12.00 pm
Note:
(A) Maximum pupils per group will be 4.
(B) Please bring along textbook and Five Year Series.
(C) If all the slots are filled, you have to see me anyday from Monday-Thursday.
For administration purposes:
These are the pupils who attend the mole concept revision on 09/02/08.
-acsyln, ronald, jolene
-keith, cheryl , natasha
-cheng hong, geok teng
Attendance is COMPLUSORY for pupils who failed the metal test or the mole concept test!!
i will be revising metals (especially displacement reactions) and simple redox ( reduction and oxidation ) on 16 Feb.
These are the time slots:
(1) 8.30 am-9.30 am
(2) 9.45 am-10.45 am
(3) 11.oo am- 12.00 pm
Note:
(A) Maximum pupils per group will be 4.
(B) Please bring along textbook and Five Year Series.
(C) If all the slots are filled, you have to see me anyday from Monday-Thursday.
For administration purposes:
These are the pupils who attend the mole concept revision on 09/02/08.
-acsyln, ronald, jolene
-keith, cheryl , natasha
-cheng hong, geok teng
Wednesday, February 6, 2008
Latest News For Sec 5 Normal Academic Science Chemistry Common Test on Week 7 / 8
The topics tested for Science Chemistry Common Test (5A) on week 7/8 are as follows:
(1) Bonding ( ionic, covalent and their properties )
(2) Mole concept
(3) Metals ( properities of metals, extraction of metals, uses of metals and recycling )
(4) simple oxidation and reduction
(5) Periodic Table
Please pass this information around:)
(1) Bonding ( ionic, covalent and their properties )
(2) Mole concept
(3) Metals ( properities of metals, extraction of metals, uses of metals and recycling )
(4) simple oxidation and reduction
(5) Periodic Table
Please pass this information around:)
Wednesday, January 30, 2008
Latest News For Normal Academic Science Chemistry Common Test on Week 7 / 8
The topics tested for Science Chemistry Common Test (4A1-4A3) on week 7/8 are as follows:
(1) ionic and covalent bonding
(2) mole concept: calculating reacting equations
(3) acids, bases and salts ( including oxides- acidic, basic and amphoteric )
Please pass this information around:)
(1) ionic and covalent bonding
(2) mole concept: calculating reacting equations
(3) acids, bases and salts ( including oxides- acidic, basic and amphoteric )
Please pass this information around:)
Saturday, January 26, 2008
Latest news for chemistry common test on week 7/8
The topics tested for Science Chemistry Common Test (4E1/4E4) on week 7/8 are as follows:
(1) ionic and covalent bonding
(2) group properties [ group 1,7,8 ]
(3) metals [ properties of metals, reactivity series of metals, extractions (esp. iron ), recycling ]
(4) oxidation and reduction
Note: Five year series will be available to you guys on thursday 31st jan 08, so you guys will be able to practice the questions. Will keep you inform what questions to practice.
Pass this info to your friends/classmates:)
(1) ionic and covalent bonding
(2) group properties [ group 1,7,8 ]
(3) metals [ properties of metals, reactivity series of metals, extractions (esp. iron ), recycling ]
(4) oxidation and reduction
Note: Five year series will be available to you guys on thursday 31st jan 08, so you guys will be able to practice the questions. Will keep you inform what questions to practice.
Pass this info to your friends/classmates:)
Some Tips for Qualitative Analysis
A lot of pupils fare badly for Qualitative Analysis.
Students are unable to choose the appropriate test for identifying the gas evolved.
Typical Scenario:
When a gas evolved from a reaction, pupils used All the various test to identify the unknown gas.
Before the correct test can be used to test for the unknown gas, the reaction stopped to produce any gas!!!!
So how?!?
You can deduce the identity of a gas ( before actually testing ) by:
*** 1.The reactions that produced the gas.
2.The odour of the gas.
3.The colour of the gas, (whereby in your syllabus), chlorine is yellowish green.
For hydrogen gas
the reagents used will surely be acids and metal strips...
if you did not used any shiny powder ( probably metals ) or shiny strips, then the test for hydrogen is NOT NECESSARY because hydrogen gas will never be produce when the reagents are not acids and metals!!! so, please do not test with burning/lighted splints.
Students are unable to choose the appropriate test for identifying the gas evolved.
Typical Scenario:
When a gas evolved from a reaction, pupils used All the various test to identify the unknown gas.
Before the correct test can be used to test for the unknown gas, the reaction stopped to produce any gas!!!!
So how?!?
You can deduce the identity of a gas ( before actually testing ) by:
*** 1.The reactions that produced the gas.
2.The odour of the gas.
3.The colour of the gas, (whereby in your syllabus), chlorine is yellowish green.
For hydrogen gas
the reagents used will surely be acids and metal strips...
if you did not used any shiny powder ( probably metals ) or shiny strips, then the test for hydrogen is NOT NECESSARY because hydrogen gas will never be produce when the reagents are not acids and metals!!! so, please do not test with burning/lighted splints.
For carbon dioxide gas
carbon dioxide only evolved when you heat a carbonate or you react an acid with a carbonate. So, if you are not using a dull powder (or dull solids) then no need to test for carbon dioxide gas!!
For oxygen gas
oxygen gas will not be produced from acid-base/acids-metal/acids-carbonate reactions!!!!
oxygen gas reactions can be very tricky....
because there are a few reactions that produce oxygen gas.
Eg- adding manganese oxide to hydrogen peroxide and heating nitrates.
Pupils always expect the glowing splint to rekindle BRIGHTLY... however, in most reactions, this does not happen.
The reason is simple.... the amount of oxygen gas produced from your 1-heap spatula and 2cm3 of solvent is not enough to produce alot of oxygen gas!!!! Should you observe a slight glow/brightens, you can safely deduce the unknown gas as oxygen.
Lastly pupils need to know HOW TO CONCENTRATE GASES
Pupils need to use their thumb to cover the openng of the test-tube to 'concentrate' the gas.
This is to ensure the gases will be enough to create a clearer result. Most of the time, pupils failed to observe the result because the gas that travels from the reacting mixture to the opening of the test-tube is too little.
hope that you find this useful!
Tuesday, January 22, 2008
Studying Strategies :)
Ever wonder why you STILL score a C5-6 grade even though you do school work/ studied at home/pay attention during lessons?
seems no justice ?!?
Well, justice can prevail ... read more to find out......
(1) Know what is the most/more important ideas of the topic
It is no use memorising the whole topic......
there are times pupils memorised chapters/practise a particular concept and spend 1 week for revision of a topic where it will only be of a weightage of less than 3 marks in exam!!!
the next question you would ask ," but we don't know what is important for the exams? "
then, you have to (1) ask the teachers; (2) see which questions are usually/ frequently tested in the past year papers!!!
(2) Know the mark allocation of the question
Most pupils waste their time by writing more than 4 sentences for a 1 mark question!!!
Pupils need to know that [1 mark] is approxiamtely 1.5 minutes.
Hence, every sentence you write will be equivalent to almost [ 1/2 mark ]. In other words, pupils should not have any 'waste move'. again, if pupils do not know the mark allocation for the question, please seek teachers advise!!!!
(3) Know how to identify the question to the chapter and to link common answers to the question
This is an extremely important strategy!!!!!
Usually, pupils failed to identify the question to the relevant chapter. As such, they have difficulty in suggesting reasonable answers.
Example,
sodium chloride and chlorine gas are substances of chloride. Explain why sodium chloride has high melting point while chlorine gas has a low melting point.
Suggested answers from pupils :
sodium is a metal and chlorine is a non-metal, hence sodium chloride is high melting point; chlorine gas is a non-metal, hence low melting point.
Does this solution make sense?!?
Firstly, this solution does not need any information from the topic-bonding. Any secondary 1/2 will be able to identify whether sodium is a metal or not from the periodic table!!!!
Strategy: When a pupil sees this question. The pupil MUST identify the topic which is bonding.
From bonding, try to recall the words-' ionic bonding' and 'covalent bonding'.... ( no other chapters talks about bonding, so it is very obvious )
from ionic bonding-- try to link it to electrostatic forces of attraction while covalent bonding, link it to weak intermolecular forces of attraction.
Generally, teachers will inform pupils to memorise the reason for high melting point. The sentence goes like this, " sodium chloride is an ionic compound, a large amount of energy is needed to overcome the strong forces of attraction between oppositely charged ions, hence high melting point. On the other hand, chlorine gas is a covalent molecule. A small amount of energy is needed to overcome the weak intermolecular forces of attraction between the molecules. Hence low melting point. "
If you can remember the topic correctly, should be able to ring a bell and will be able to write a few sentences from the 'standard answers by teachers'......
that's all for my sharing :)
May the force be with you
seems no justice ?!?
Well, justice can prevail ... read more to find out......
(1) Know what is the most/more important ideas of the topic
It is no use memorising the whole topic......
there are times pupils memorised chapters/practise a particular concept and spend 1 week for revision of a topic where it will only be of a weightage of less than 3 marks in exam!!!
the next question you would ask ," but we don't know what is important for the exams? "
then, you have to (1) ask the teachers; (2) see which questions are usually/ frequently tested in the past year papers!!!
(2) Know the mark allocation of the question
Most pupils waste their time by writing more than 4 sentences for a 1 mark question!!!
Pupils need to know that [1 mark] is approxiamtely 1.5 minutes.
Hence, every sentence you write will be equivalent to almost [ 1/2 mark ]. In other words, pupils should not have any 'waste move'. again, if pupils do not know the mark allocation for the question, please seek teachers advise!!!!
(3) Know how to identify the question to the chapter and to link common answers to the question
This is an extremely important strategy!!!!!
Usually, pupils failed to identify the question to the relevant chapter. As such, they have difficulty in suggesting reasonable answers.
Example,
sodium chloride and chlorine gas are substances of chloride. Explain why sodium chloride has high melting point while chlorine gas has a low melting point.
Suggested answers from pupils :
sodium is a metal and chlorine is a non-metal, hence sodium chloride is high melting point; chlorine gas is a non-metal, hence low melting point.
Does this solution make sense?!?
Firstly, this solution does not need any information from the topic-bonding. Any secondary 1/2 will be able to identify whether sodium is a metal or not from the periodic table!!!!
Strategy: When a pupil sees this question. The pupil MUST identify the topic which is bonding.
From bonding, try to recall the words-' ionic bonding' and 'covalent bonding'.... ( no other chapters talks about bonding, so it is very obvious )
from ionic bonding-- try to link it to electrostatic forces of attraction while covalent bonding, link it to weak intermolecular forces of attraction.
Generally, teachers will inform pupils to memorise the reason for high melting point. The sentence goes like this, " sodium chloride is an ionic compound, a large amount of energy is needed to overcome the strong forces of attraction between oppositely charged ions, hence high melting point. On the other hand, chlorine gas is a covalent molecule. A small amount of energy is needed to overcome the weak intermolecular forces of attraction between the molecules. Hence low melting point. "
If you can remember the topic correctly, should be able to ring a bell and will be able to write a few sentences from the 'standard answers by teachers'......
that's all for my sharing :)
May the force be with you
Monday, January 21, 2008
Replying Ronald's Question: How do we know the valencies of ions?
Ronald asked:
Ms Pang, hw u noe whether the Element electron charge is -2, -1, +1 or +2
My reply:
an ion ( not element ) will have a charge of minus or plus depends whether it is a metal or non-metal.
For metal, it tends to form ions of charge +1, +2, +3 ( cations- lose electrons )
For non-metal, it tends to form ions of charge -1,-2 ( anions - gain electrons )
ms pang:)
Ms Pang, hw u noe whether the Element electron charge is -2, -1, +1 or +2
My reply:
an ion ( not element ) will have a charge of minus or plus depends whether it is a metal or non-metal.
For metal, it tends to form ions of charge +1, +2, +3 ( cations- lose electrons )
For non-metal, it tends to form ions of charge -1,-2 ( anions - gain electrons )
ms pang:)
Monday, January 30, 2006
ALCOHOL
Formula of alcohol :
CnH2n+1OH
Nomenclature
all alkanes begin with the prefix as mentioned below and ending with -ol
( 1 carbon atom) methan-
( 2 carbon atoms ) ethan-
( 3 carbon atoms ) propan-
( 4 carbon atoms ) butan-
( 5 carbon atoms ) pentan-
( 6 carbon atoms ) hexan-
( 7 carbon atoms ) heptan-
( 8 carbon atoms ) octan -
( 9 carbon atoms ) nonan-
(10 carbon atoms ) decan-
Properties of alkene
1) Combustion
Burns in plentify supply of air, it produces carbon dioxide and water.If INCOMPLETE COMBUSTION, it gives soot, carbon monoxide, carbon dioxide and water.
2) Oxidation
(a) ethanol oxidised to ethanoic acid by warming with acidified potassium dichromate.
(b) ethanol can be oxidised to ethanoic acid using air by the bacteria in the air.
3) Formation of esters
Alcohol reacts with carboxylic acids in the presence of a few drops of concentrated sulphuricacid as a catalyst to form esters and water.
CnH2n+1OH
Nomenclature
all alkanes begin with the prefix as mentioned below and ending with -ol
( 1 carbon atom) methan-
( 2 carbon atoms ) ethan-
( 3 carbon atoms ) propan-
( 4 carbon atoms ) butan-
( 5 carbon atoms ) pentan-
( 6 carbon atoms ) hexan-
( 7 carbon atoms ) heptan-
( 8 carbon atoms ) octan -
( 9 carbon atoms ) nonan-
(10 carbon atoms ) decan-
Properties of alkene
1) Combustion
Burns in plentify supply of air, it produces carbon dioxide and water.If INCOMPLETE COMBUSTION, it gives soot, carbon monoxide, carbon dioxide and water.
2) Oxidation
(a) ethanol oxidised to ethanoic acid by warming with acidified potassium dichromate.
(b) ethanol can be oxidised to ethanoic acid using air by the bacteria in the air.
3) Formation of esters
Alcohol reacts with carboxylic acids in the presence of a few drops of concentrated sulphuricacid as a catalyst to form esters and water.
ALKANES
Formula of Alkane :
CnH2n+2
Nomenclature ( Naming )
all alkanes begin with the prefix as mentioned below and ending with -ane
(1 carbon atom) meth-
(2 carbon atoms ) eth -
( 3 carbon atoms ) prop-
( 4 carbon atoms ) but -
( 5 carbon atoms ) pent -
( 6 carbon atoms ) hex -
( 7 carbon atoms ) hept-
( 8 carbon atoms ) oct -
( 9 carbon atoms ) non-
(10 carbon atoms ) dec-
Properties of Alkane:
1) Burns in plentify supply of air, it produces carbon dioxide and water.If INCOMPLETE COMBUSTION, it gives soot, carbon monoxide,carbon dioxide and water.
2) One reaction:Free radical Substitution
Alkane will react with Chlorine in UV light conditions ( means sunlight ) to form a variety of products:
Eg:
CH4 + Cl2 ---> CH3Cl + HCl ------ equation (1)
CH3Cl + Cl2 ---> CH2Cl2 + HCl ------ equation (2)
CH2Cl2 + Cl2 ---> CHCl3 + HCl ------- equation (3)
CHCl3 + Cl2 ---> CCl4 + HCl ----- equation (4)
Lastly, in exam, you are EXPECTED to name, form equations and draw the structure!
CnH2n+2
Nomenclature ( Naming )
all alkanes begin with the prefix as mentioned below and ending with -ane
(1 carbon atom) meth-
(2 carbon atoms ) eth -
( 3 carbon atoms ) prop-
( 4 carbon atoms ) but -
( 5 carbon atoms ) pent -
( 6 carbon atoms ) hex -
( 7 carbon atoms ) hept-
( 8 carbon atoms ) oct -
( 9 carbon atoms ) non-
(10 carbon atoms ) dec-
Properties of Alkane:
1) Burns in plentify supply of air, it produces carbon dioxide and water.If INCOMPLETE COMBUSTION, it gives soot, carbon monoxide,carbon dioxide and water.
2) One reaction:Free radical Substitution
Alkane will react with Chlorine in UV light conditions ( means sunlight ) to form a variety of products:
Eg:
CH4 + Cl2 ---> CH3Cl + HCl ------ equation (1)
CH3Cl + Cl2 ---> CH2Cl2 + HCl ------ equation (2)
CH2Cl2 + Cl2 ---> CHCl3 + HCl ------- equation (3)
CHCl3 + Cl2 ---> CCl4 + HCl ----- equation (4)
Lastly, in exam, you are EXPECTED to name, form equations and draw the structure!
ALKENES
Formula of alkene :
CnH2n
Nomenclature
all alkanes begin with the prefix as mentioned below and ending with -ene
there is no methene ( 1 carbon )
(2 carbon atoms ) eth-
( 3 carbon atoms ) prop-
( 4 carbon atoms ) but-
( 5 carbon atoms ) pent-
( 6 carbon atoms ) hex-
( 7 carbon atoms ) hept-
( 8 carbon atoms ) oct-
( 9 carbon atoms ) non-
(10 carbon atoms ) dec-
Properties of alkene
1) Combustion
Burns in plentify supply of air, it produces carbon dioxide and water.
If INCOMPLETE COMBUSTION, it gives soot, carbon monoxide, carbon dioxide and water.
2) Hydrogenation
C2H4 + H2 ---> C2H6 (ethane)
3) Bromination
C2H4 + Br2 ---> C2H4Br2
** This is bromine test: used to distinguish between alkane and alkene ** ( Typical Structure Question!)
Alkene: Aqueous bromine will decolourised.
Alkane: Aqueous bromine remains unchanged.
4) Hydration
C2H4 + H2O ---> C2H5OH (ethanol)
Another method to prepare ethanol is 'fermentation'
C6H12O6 ---> 2 C2H5OH + 2 CO2
Conditions: yeast and temperature: 25'C.
5) Cracking
To break less useful linger chains into smaller useful fractions.
Conditions: 400°C - 700°C , silicon dioxide /aluminum oxide as catalyst.
CnH2n
Nomenclature
all alkanes begin with the prefix as mentioned below and ending with -ene
there is no methene ( 1 carbon )
(2 carbon atoms ) eth-
( 3 carbon atoms ) prop-
( 4 carbon atoms ) but-
( 5 carbon atoms ) pent-
( 6 carbon atoms ) hex-
( 7 carbon atoms ) hept-
( 8 carbon atoms ) oct-
( 9 carbon atoms ) non-
(10 carbon atoms ) dec-
Properties of alkene
1) Combustion
Burns in plentify supply of air, it produces carbon dioxide and water.
If INCOMPLETE COMBUSTION, it gives soot, carbon monoxide, carbon dioxide and water.
2) Hydrogenation
C2H4 + H2 ---> C2H6 (ethane)
3) Bromination
C2H4 + Br2 ---> C2H4Br2
** This is bromine test: used to distinguish between alkane and alkene ** ( Typical Structure Question!)
Alkene: Aqueous bromine will decolourised.
Alkane: Aqueous bromine remains unchanged.
4) Hydration
C2H4 + H2O ---> C2H5OH (ethanol)
Another method to prepare ethanol is 'fermentation'
C6H12O6 ---> 2 C2H5OH + 2 CO2
Conditions: yeast and temperature: 25'C.
5) Cracking
To break less useful linger chains into smaller useful fractions.
Conditions: 400°C - 700°C , silicon dioxide /aluminum oxide as catalyst.
OXIDATION & REDUCTION
There are basically 4 definitions of oxidation and reduction:
OXIDATION
1) Increase in oxidation states
Eg: Fe 2+ ---> Fe 3+
An increase of oxidation staes from 2+ to 3+ ( obvious, isn't it? )
2) Gain of oxygen atoms
Eg: Pb + CuO --> PbO + Cu
In this case, Lead (Pb) has gain 1 oxygen atom to form lead(II) oxide (PbO)
3) Lost of hydrogen atoms
Eg: 2 H2S (g) + SO2(g) ---> 2H2O(l) + 3S (s)
In this case, hydrogen sulphide (H2S) has lost 2 hydrogen atoms to form sulphur (S)
Note: do not be CONFUSED by the ratio: 2H2S.
We are interested in the formula, H2S instead!
4) Loss of electrons
Actually, if you look closely, the LOST of electrons is similar to the oxidation states!!!
Why Do I Say That?
Consider this example,
Fe 2+ ---> Fe 3+2+ means lost of 2 electrons and 3+ means lost of 3 electrons.In this case, we say that Fe 2+ is oxidised to Fe 3+.
Compare the oxidation states, isn't 2+ a gain of OXIDATION STATES to 3+ ??
Similarly,
REDUCTION
1) Decrease in oxidation states
Eg: Zn 2+ ---> Zn
From oxidation states of 2+ to 0 ( a decrease in oxidation states )
2) Loss of oxygen atoms
Eg: Pb + CuO ---> PbO + Cu
Copper (II) oxide has lost 1 oxygen atom to form Cu
3) Gain in hydrogen atoms
Eg: N2 + 3H2 ---> 2 NH3
Nitrogen (N2) has gain 2 hydrogen atoms to form ammonia (NH3)
4) Gain of electrons
Eg: Zn 2+ + 2 e- ---> Zn
Zinc ion has accepted 2 electrons to become Zinc ztom
or
Zinc ion has decrease in its oxidation state from 2+ to zero.
( the first rule about decrease in oxidation states )
OXIDATION
1) Increase in oxidation states
Eg: Fe 2+ ---> Fe 3+
An increase of oxidation staes from 2+ to 3+ ( obvious, isn't it? )
2) Gain of oxygen atoms
Eg: Pb + CuO --> PbO + Cu
In this case, Lead (Pb) has gain 1 oxygen atom to form lead(II) oxide (PbO)
3) Lost of hydrogen atoms
Eg: 2 H2S (g) + SO2(g) ---> 2H2O(l) + 3S (s)
In this case, hydrogen sulphide (H2S) has lost 2 hydrogen atoms to form sulphur (S)
Note: do not be CONFUSED by the ratio: 2H2S.
We are interested in the formula, H2S instead!
4) Loss of electrons
Actually, if you look closely, the LOST of electrons is similar to the oxidation states!!!
Why Do I Say That?
Consider this example,
Fe 2+ ---> Fe 3+2+ means lost of 2 electrons and 3+ means lost of 3 electrons.In this case, we say that Fe 2+ is oxidised to Fe 3+.
Compare the oxidation states, isn't 2+ a gain of OXIDATION STATES to 3+ ??
Similarly,
REDUCTION
1) Decrease in oxidation states
Eg: Zn 2+ ---> Zn
From oxidation states of 2+ to 0 ( a decrease in oxidation states )
2) Loss of oxygen atoms
Eg: Pb + CuO ---> PbO + Cu
Copper (II) oxide has lost 1 oxygen atom to form Cu
3) Gain in hydrogen atoms
Eg: N2 + 3H2 ---> 2 NH3
Nitrogen (N2) has gain 2 hydrogen atoms to form ammonia (NH3)
4) Gain of electrons
Eg: Zn 2+ + 2 e- ---> Zn
Zinc ion has accepted 2 electrons to become Zinc ztom
or
Zinc ion has decrease in its oxidation state from 2+ to zero.
( the first rule about decrease in oxidation states )
SPEED OF REACTIONS
** IF THE QUESTION STATES THE USE OF COLLISION THEORY TO EXPLAIN THE FACTORS AFFECTING THE SPEED OF REACTION, PLEASE EXPLAIN USING THE PARTICLES!!!**
(Typical Structure Question!)
Factors affecting rate of reaction:
1) CONCENTRATION
* EXPLANATION *
The greater the number of particles, the more frequent is the collision,-----> the faster the speed of reaction.
2) EFFECTIVE SURFACE AREAS OF REACTANTS
* EXPLANATION *
The greater the effective surface area of reactants,the more frequent is the collision-----> the faster the speed of reaction.
3) TEMPERATURE
* EXPLANATION *
The higher the temperature, the greater the amount of energy the paricles have, the frequent is the collision,-----> the faster the speed of reaction.
4) CATALYST
* EXPLANATION *
The use of catalyst increases the speed of reaction.
Note: Catalyst is never used up in a reaction!!!
(Typical Structure Question!)
Factors affecting rate of reaction:
1) CONCENTRATION
* EXPLANATION *
The greater the number of particles, the more frequent is the collision,-----> the faster the speed of reaction.
2) EFFECTIVE SURFACE AREAS OF REACTANTS
* EXPLANATION *
The greater the effective surface area of reactants,the more frequent is the collision-----> the faster the speed of reaction.
3) TEMPERATURE
* EXPLANATION *
The higher the temperature, the greater the amount of energy the paricles have, the frequent is the collision,-----> the faster the speed of reaction.
4) CATALYST
* EXPLANATION *
The use of catalyst increases the speed of reaction.
Note: Catalyst is never used up in a reaction!!!
AIR
Composition of air
nitrogen- 78%
oxygen - 21%
other gases- 1% ---> carbon dioxide-0.03%---> noble gases - mainly argon.
NOTE: AIR DOES NOT CONTAIN HYDROGEN!!!!!!!
POLLUTANTS
For pollutants, pupils are expected to be able to least 2 pollutants: its sources, effects and solutions. (Questions on air have become very popular in examinations)
CARBON MONOXIDE
Source: incomplete combustion of fuels in vehicle engines
Solution:
1) ensure complete combustion of fuels
2) attach catalytic converter to vehicle engines.
OXIDES OF NITROGEN
Source:
1) combustion of fuel in vehicle engines at high temperature
2) lighting
Solution:
Fit catalytic converter to vehicle engines.
ACID RAIN
1) when sulphur dioxide dissolves in rain, sulphuric acid is formed.
2) when oxides of nitrogen dissolves in rain, nitric acid is formed.
(1) + (2) --- > ACID RAIN
Effects Of Acid Rain:
(1) Corrode buildings,
(2) corrode limestone structures,
(3) damage to trees and
(4) marine lives.
nitrogen- 78%
oxygen - 21%
other gases- 1% ---> carbon dioxide-0.03%---> noble gases - mainly argon.
NOTE: AIR DOES NOT CONTAIN HYDROGEN!!!!!!!
POLLUTANTS
For pollutants, pupils are expected to be able to least 2 pollutants: its sources, effects and solutions. (Questions on air have become very popular in examinations)
CARBON MONOXIDE
Source: incomplete combustion of fuels in vehicle engines
Solution:
1) ensure complete combustion of fuels
2) attach catalytic converter to vehicle engines.
OXIDES OF NITROGEN
Source:
1) combustion of fuel in vehicle engines at high temperature
2) lighting
Solution:
Fit catalytic converter to vehicle engines.
ACID RAIN
1) when sulphur dioxide dissolves in rain, sulphuric acid is formed.
2) when oxides of nitrogen dissolves in rain, nitric acid is formed.
(1) + (2) --- > ACID RAIN
Effects Of Acid Rain:
(1) Corrode buildings,
(2) corrode limestone structures,
(3) damage to trees and
(4) marine lives.
EXTRACTION OF METALS
Extraction of Iron
TYPICAL STRUCTURED/ ESSAY QUESTIONS
Question: Describe with the aid of equations the essential reactions in the extraction of iron.
1) Iron ore (haematite), coke and limestone are added to a blastfurnace.
2) Coke reacts with the air to form carbon dioxide.
3) Coke reacts with more carbon dioxide to form carbon monoxide.
4) Carbon monoxide reacts with iron ore to form iron and carbon dioxide gas.
5) Limestone decomposes to form calcium oxide and carbon dioxide.
6) Calcium oxide reacts with silicn dioxide to form slag.
Typical questions associating with extraction of iron:
(a) Name of the iron ore = haematite
(b) Why is limestone used in the extraction = to remove impurities ( acidic oxide, silicon dioxide )
_______________________________________________
Note:the extraction of metal depends on the reactivity of the metal.
Electrolysis of molten chlorides
Potassium, Sodium, Calcium, Magnesium, Aluminum
Heating with carbon
Zinc, Iron, Lead, Coppper
Uncombined in the ground
Silver, Gold, Platinum
TYPICAL STRUCTURED/ ESSAY QUESTIONS
Question: Describe with the aid of equations the essential reactions in the extraction of iron.
1) Iron ore (haematite), coke and limestone are added to a blastfurnace.
2) Coke reacts with the air to form carbon dioxide.
3) Coke reacts with more carbon dioxide to form carbon monoxide.
4) Carbon monoxide reacts with iron ore to form iron and carbon dioxide gas.
5) Limestone decomposes to form calcium oxide and carbon dioxide.
6) Calcium oxide reacts with silicn dioxide to form slag.
Typical questions associating with extraction of iron:
(a) Name of the iron ore = haematite
(b) Why is limestone used in the extraction = to remove impurities ( acidic oxide, silicon dioxide )
_______________________________________________
Note:the extraction of metal depends on the reactivity of the metal.
Electrolysis of molten chlorides
Potassium, Sodium, Calcium, Magnesium, Aluminum
Heating with carbon
Zinc, Iron, Lead, Coppper
Uncombined in the ground
Silver, Gold, Platinum
ENERGY FROM CHEMICALS
EXOTHERMIC ( EXit )
Heat energy is released.
Egs: acid and metal reactions, neutralization, condensation, freezing and bond-making
Heat of Reaction (Enthalpy change) = negative
Tips for remembering: When two persons get together ( bond-making), they are in love and they will release 'sparks' of love ( 'Heat energy release') [ laugh]
ENDOTHERMIC
Heat energy is absorbed.
Eg: decomposition, melting, boiling, bond-breaking
Heat of Reaction ( Enthalpy change ) = positive
Tips for remembering: When a couple wants to break up ( bond-breaking), they need to gather all their complains and greviances to quarrel ('Heat energy gain') [laugh]
Heat energy is released.
Egs: acid and metal reactions, neutralization, condensation, freezing and bond-making
Heat of Reaction (Enthalpy change) = negative
Tips for remembering: When two persons get together ( bond-making), they are in love and they will release 'sparks' of love ( 'Heat energy release') [ laugh]
ENDOTHERMIC
Heat energy is absorbed.
Eg: decomposition, melting, boiling, bond-breaking
Heat of Reaction ( Enthalpy change ) = positive
Tips for remembering: When a couple wants to break up ( bond-breaking), they need to gather all their complains and greviances to quarrel ('Heat energy gain') [laugh]
GROUP PROPERTIES
Typical Exam Questions!!!!(STR/ESSAY)
Group I ( alkali metals)
It is known as alkali metals because it reacts with water to form HYDROXIDES and hydrogen gas.
They are soft, low densities ( hence can be cut by knife ), having charges (+1) and the melting point decreases down the group. They are very reactive hence they need to be stored under oil to prevent reaction with air and water.
An Easy Way For Pupils To Remember the reactivity.......
'F' is the MOST REACTIVE !!!!!
For group I, Francium is the most reactive!!!! ( hence reactivity increases down the group )
Pupils are required to state the way the element react with water!!!!
Lithium reacts fast.
Sodium reacts quickly, catches fire sometimes explodes
Potassium reacts EXTREMELY FAST; catches fire and then EXPLODES.
As for rubidium, caesium and francium.... the reactivity will be explosion because they are more reactive than potassium.
Group VII ( halogen)
Each molecule is diatomic (F2, Cl2, Br2, I2, At2), having charges of (-1) and the boiling points increases down the group. They are very reactive and react VIGOROUSLY with metals to form ionic salts. Reactivity decreases down the group.
Remember: F is the most reactive.
Hence Fluorine is the most reactive, followered by chlorine, bromine, iodine and the least reactive is astatine.
As for the colours, it darkens down the group.
Fluorine is light yellow
Chlorine is yellow green
Bromine is brown
Iodine is dark purple ( black is acceptable)
Astatine is black
Since the boiling points increases down the group, the states are as follows:
Fluorine-(gas)
Chlorine-(gas)
Bromine-(liquid)
Iodine-(solid)
Astatine-(solid)
Since reactivity decreases down group 7, A MORE REATIVITY HALOGEN WILL BE ABLE TO DISPLACE A LESS REACTIVE HALOGEN FROM AN AQUEOUS SOLUTIONS OF ITS SALT.
This means that fluorine is able to displace (kick out) all the rest of the elements from group 7:
F2 (g) + 2 NaCl(aq) ----> 2 NaF(aq) + Cl2(aq)
However, a less reactive halogen will not be able to displace a more reactive halogen:
Cl2(g) + NaF (aq) ---> no reaction
GROUP 8 ( NOBLE GASES )
These elements are not able to combine with other atoms because of its stable electronic configuration ( octet structure can be used to replace 'stable-electronic configuration').
Hence group 8 elements are MONOATOMIC.
Pupils will need to know the uses:
Helium-hot air balloon
Neon- advertising lights
Argon / Neon - in light bulbs
Argon - manufacturing of steel ( flush air from molten steel to protect it from further reaction of the air )
Group I ( alkali metals)
It is known as alkali metals because it reacts with water to form HYDROXIDES and hydrogen gas.
They are soft, low densities ( hence can be cut by knife ), having charges (+1) and the melting point decreases down the group. They are very reactive hence they need to be stored under oil to prevent reaction with air and water.
An Easy Way For Pupils To Remember the reactivity.......
'F' is the MOST REACTIVE !!!!!
For group I, Francium is the most reactive!!!! ( hence reactivity increases down the group )
Pupils are required to state the way the element react with water!!!!
Lithium reacts fast.
Sodium reacts quickly, catches fire sometimes explodes
Potassium reacts EXTREMELY FAST; catches fire and then EXPLODES.
As for rubidium, caesium and francium.... the reactivity will be explosion because they are more reactive than potassium.
Group VII ( halogen)
Each molecule is diatomic (F2, Cl2, Br2, I2, At2), having charges of (-1) and the boiling points increases down the group. They are very reactive and react VIGOROUSLY with metals to form ionic salts. Reactivity decreases down the group.
Remember: F is the most reactive.
Hence Fluorine is the most reactive, followered by chlorine, bromine, iodine and the least reactive is astatine.
As for the colours, it darkens down the group.
Fluorine is light yellow
Chlorine is yellow green
Bromine is brown
Iodine is dark purple ( black is acceptable)
Astatine is black
Since the boiling points increases down the group, the states are as follows:
Fluorine-(gas)
Chlorine-(gas)
Bromine-(liquid)
Iodine-(solid)
Astatine-(solid)
Since reactivity decreases down group 7, A MORE REATIVITY HALOGEN WILL BE ABLE TO DISPLACE A LESS REACTIVE HALOGEN FROM AN AQUEOUS SOLUTIONS OF ITS SALT.
This means that fluorine is able to displace (kick out) all the rest of the elements from group 7:
F2 (g) + 2 NaCl(aq) ----> 2 NaF(aq) + Cl2(aq)
However, a less reactive halogen will not be able to displace a more reactive halogen:
Cl2(g) + NaF (aq) ---> no reaction
GROUP 8 ( NOBLE GASES )
These elements are not able to combine with other atoms because of its stable electronic configuration ( octet structure can be used to replace 'stable-electronic configuration').
Hence group 8 elements are MONOATOMIC.
Pupils will need to know the uses:
Helium-hot air balloon
Neon- advertising lights
Argon / Neon - in light bulbs
Argon - manufacturing of steel ( flush air from molten steel to protect it from further reaction of the air )
PERIODIC TABLE
The elements in the periodic table are arranging according to INCREASING PROTON NUMBERS.
The vertical columns are known as Groups while the horizontal rows are known as Periods.
Elements of the same group have the same number of valence electrons ( outershell electrons)
Eg:
All ements of group 1 have 1 valence electrons;
All elements of group 2 have 2 valence electrons.
Elements of the same period have the same number of electron shells.
Eg:
All elements of period 1 ( Hydrogen and Helium ) have 1 electron shell.
All elements of period 2 (Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, Sulphur, Fluorine, Neon ) have 2 electron shells.
There exist a group of elements without any grouping.
These are the transition metals.
Transition metals are characterized by their variable ( more than 1 ) valencies.
Eg:
iron ion exist as iron (II) ion and iron (III) ion;
copper ion exist as copper(I) ion and copper(II) ion.
The vertical columns are known as Groups while the horizontal rows are known as Periods.
Elements of the same group have the same number of valence electrons ( outershell electrons)
Eg:
All ements of group 1 have 1 valence electrons;
All elements of group 2 have 2 valence electrons.
Elements of the same period have the same number of electron shells.
Eg:
All elements of period 1 ( Hydrogen and Helium ) have 1 electron shell.
All elements of period 2 (Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, Sulphur, Fluorine, Neon ) have 2 electron shells.
There exist a group of elements without any grouping.
These are the transition metals.
Transition metals are characterized by their variable ( more than 1 ) valencies.
Eg:
iron ion exist as iron (II) ion and iron (III) ion;
copper ion exist as copper(I) ion and copper(II) ion.
STRUCTURE OF ATOMS
(Typical MCQ Question!!)
Location of Particles
Protons, neutrons are found in nucleus
Electrons orbit in electron shells
Mass of Particles
Proton = 1
Neutron = 1
Electron = 1/1840 ~ 0
Charges of Particles
Proton = +1
Neutron = 0
Electron = -1
Isotopes (Typical Structure Question!! )
Isotopes are atoms of the same element with different nucleon numbers but same proton number.
Eg: Carbon-12, Carbon-13, Carbon-14
Location of Particles
Protons, neutrons are found in nucleus
Electrons orbit in electron shells
Mass of Particles
Proton = 1
Neutron = 1
Electron = 1/1840 ~ 0
Charges of Particles
Proton = +1
Neutron = 0
Electron = -1
Isotopes (Typical Structure Question!! )
Isotopes are atoms of the same element with different nucleon numbers but same proton number.
Eg: Carbon-12, Carbon-13, Carbon-14
CHEMICAL BONDS
Ionic Compounds
Ionic compounds are formed by metal (gp 1-3) and non-metal (gp 4-7)
Properties
-High melting point and boiling point ( considered as one point in exam ).
-Soluble in water.
-Conduct electricity in molten (hot liquid ) and in aqueous states
Note: does not conduct electricity in solid states!!!
Metal conduct electricity in molten and in solid states.
Covalent Compounds
Covalent compounds are formed only by non-metal elements.
Properties
-Low melting and boiling points
-Soluble in organic solvents
-Poor conductor of electricity
EXCEPTION: HCl is a good conductor of electricity.
Reason: When HCl dissolves in water, it dissociates to produce H+ and Cl-. It is the free mobile ions that conduct electricity! (Typical MCQ Question! )
(Typical Structure Question)
Question: Both sodium chloride and chlorine gas are compounds of chlorine; sodium chloride exist as a solid while chlorine exist as a gas. Explain why.
Answer:
Sodium chloride is an ionic compound [ 1mark ]. A large amount of energy is needed to overcome the strong electrostatic forces of attraction between oppositely charged ions [ 1mark] . Hence high melting point. This is why it exist as a solid at room
temperature.
Chlorine gas is a covalent substance [ 1mark]. A small amount of energy is needed to overcome the weak intermolecular force of attraction between the molecules [ 1mark]. Hence low melting point. This is why it exist as a gas at room temperature.
Note: Although 'Hence high melting point. This is why it exist as a solid at room temperature.' has no mark allocation, this phrase has to be included for the completeness of answer!
Ionic compounds are formed by metal (gp 1-3) and non-metal (gp 4-7)
Properties
-High melting point and boiling point ( considered as one point in exam ).
-Soluble in water.
-Conduct electricity in molten (hot liquid ) and in aqueous states
Note: does not conduct electricity in solid states!!!
Metal conduct electricity in molten and in solid states.
Covalent Compounds
Covalent compounds are formed only by non-metal elements.
Properties
-Low melting and boiling points
-Soluble in organic solvents
-Poor conductor of electricity
EXCEPTION: HCl is a good conductor of electricity.
Reason: When HCl dissolves in water, it dissociates to produce H+ and Cl-. It is the free mobile ions that conduct electricity! (Typical MCQ Question! )
(Typical Structure Question)
Question: Both sodium chloride and chlorine gas are compounds of chlorine; sodium chloride exist as a solid while chlorine exist as a gas. Explain why.
Answer:
Sodium chloride is an ionic compound [ 1mark ]. A large amount of energy is needed to overcome the strong electrostatic forces of attraction between oppositely charged ions [ 1mark] . Hence high melting point. This is why it exist as a solid at room
temperature.
Chlorine gas is a covalent substance [ 1mark]. A small amount of energy is needed to overcome the weak intermolecular force of attraction between the molecules [ 1mark]. Hence low melting point. This is why it exist as a gas at room temperature.
Note: Although 'Hence high melting point. This is why it exist as a solid at room temperature.' has no mark allocation, this phrase has to be included for the completeness of answer!
STATES SYMBOLS
STATES SYMBOLS
(s) represents solid states
(l) represents liquid states
(g) represents gaseous states
(aq) represents aqueous states - means dissolved in water.
Question 1: 'Is water in aqueous state?'
Answer: No!! Simply because water cannot dissolve in water!!!
Question2: ' Is there any difference between gases vs gaseous?'
Answer: gases are particles that can move freely, while gaseous is to describe the state of the particles.
(s) represents solid states
(l) represents liquid states
(g) represents gaseous states
(aq) represents aqueous states - means dissolved in water.
Question 1: 'Is water in aqueous state?'
Answer: No!! Simply because water cannot dissolve in water!!!
Question2: ' Is there any difference between gases vs gaseous?'
Answer: gases are particles that can move freely, while gaseous is to describe the state of the particles.
ELEMENTS, MIXTURES & COMPOUNDS
Element
An element is a substance that cannot be broken down into simpler substances by chemical means.
Eg: oxygen (O2), carbon (C), sulphur (S)
Note: Elements can be found in the Periodic Table.
Do not be confused:
1) An element can exist as molecules.Eg: hydrogen (H2), nitrogen (N2)
Molecule simply means more than 1 atom.
So, you can have the same type of atoms ( O2, N2, H2 , S8 ) or different types of atoms (CO2, CH4, H2O)
Compound
When it is made up by different types of atoms joined together chemically, it becomes a compound.
In this case, CO2 and CH4 are compounds.
A compound is a substance made up by more than 1 elements joined chemically together.
Eg: Calcium carbonate (CaCO3) ~contains 3 elements namely calcium(Ca), carbon (C) and oxygen (O)
Number of atoms in CaCO3 = 1+1+ 3(1) = 5 atoms
MIXTURE
Made up by at least 2 substances not joined together chemically.
Mixture can be catagorised by three types:
1) Element + Element
Eg: Iron(Fe) + Carbon(C)
2) Element + Compound
Eg: Copper (Cu)+ Water (H2O)
3) Compound + Compound
Eg: sodium chloride (NaCl) + water (H2O)
Common mistake made by students:
'A mixture can ONLY be separated by physical means'. (WRONG!!)
* EXPLANATION *
A mixture can also be separated by chemical means!!Compound is a substance that cannot be separated by physical means.
An element is a substance that cannot be broken down into simpler substances by chemical means.
Eg: oxygen (O2), carbon (C), sulphur (S)
Note: Elements can be found in the Periodic Table.
Do not be confused:
1) An element can exist as molecules.Eg: hydrogen (H2), nitrogen (N2)
Molecule simply means more than 1 atom.
So, you can have the same type of atoms ( O2, N2, H2 , S8 ) or different types of atoms (CO2, CH4, H2O)
Compound
When it is made up by different types of atoms joined together chemically, it becomes a compound.
In this case, CO2 and CH4 are compounds.
A compound is a substance made up by more than 1 elements joined chemically together.
Eg: Calcium carbonate (CaCO3) ~contains 3 elements namely calcium(Ca), carbon (C) and oxygen (O)
Number of atoms in CaCO3 = 1+1+ 3(1) = 5 atoms
MIXTURE
Made up by at least 2 substances not joined together chemically.
Mixture can be catagorised by three types:
1) Element + Element
Eg: Iron(Fe) + Carbon(C)
2) Element + Compound
Eg: Copper (Cu)+ Water (H2O)
3) Compound + Compound
Eg: sodium chloride (NaCl) + water (H2O)
Common mistake made by students:
'A mixture can ONLY be separated by physical means'. (WRONG!!)
* EXPLANATION *
A mixture can also be separated by chemical means!!Compound is a substance that cannot be separated by physical means.
FORMULAS
All ions formed from:
group 1 ,(H+), (NH4+) have charges (+1)
group 2, Pb2+, Cu2+,Fe2+ have charges (+2)
group 3, have charges (+3)
group 6, (CO32-), (SO42- ) have charges (-2)
group 7, (OH-), (NO3-) have charges (-1)
* certain ions have various valency:
(Fe2+, Fe3+) , (Pb2+,Pb4+)
group 1 ,(H+), (NH4+) have charges (+1)
group 2, Pb2+, Cu2+,Fe2+ have charges (+2)
group 3, have charges (+3)
group 6, (CO32-), (SO42- ) have charges (-2)
group 7, (OH-), (NO3-) have charges (-1)
* certain ions have various valency:
(Fe2+, Fe3+) , (Pb2+,Pb4+)
PURIFICATION
1) FILTRATION
Eg: sand from sand + water mixture
2) CRYSTALLISATION
Eg: separates dyes or colour from food/ ink/ pigments,check amounts of pesticides in vegetables, check if medicine contains banned drugs etc
Eg: sand from sand + water mixture
2) CRYSTALLISATION
Eg: copper(II)sulphate from impure copper(II)sulphate mixture
* Crystallisation is usually carried out with filtration.
3) DISTILLATION
Defn: to obtain pure liquid from a solution of solute
Eg: water from sea water
4) FRACTIONAL DISTILLATION
Defn: to separate liquids with different boiling points
Eg:
(i) ethanol from ethanol(78'C) + water(100'C)
(ii) crude oil into petrol, kerosene, lubicating oil etc
(iii) air into nitrogen, oxygen, carbon dioxide etc
5) CHROMATOGRAPHY
Defn: a method to separate and identify mixturesEg: separates dyes or colour from food/ ink/ pigments,check amounts of pesticides in vegetables, check if medicine contains banned drugs etc
(6) SUBLIMATION
Defn: a process in which substances changes from solid states to gaseous states through heating.
Eg: Ammonium chlorides ( NH4Cl ), dry ice ( solid CO2) ,naphthalene ( mothballs ), iodine
To test if a substance is pure / impure ( typical MCQ question!! )
CHECK IF IT HAS A FIXED BOILING / MELTING POINT------> IF IT IS PURE, IT WILL HAVE A FIXED MP/BP
Disclaimer: Picture are obtained from these websites-
GCSE Chemistry noteswww.wpbschoolhouse.btinternet.co.uk/page01/ElCpdMix/EleCmdMix.htm
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