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:)
Wednesday, January 30, 2008
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:)
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