(2) C
reason: filtration, crystalization and distillation are physical methods. Can only separate mixtures not the individual elements within a compound.
(3) D
reason: elimination method: Aq NaCl and Molten NaCl will have products at electrodes. Bromine is a poor conductor of electricity. Mercury is a metal, just that it exisit in liquid state and it can conduct electricity. So, of course it can conduct electricity. Actually, this question can be seen as a electricity question.
(4) C
reason: cations are attracted to cathode: only option C is cation.
(5) D
reason: this is a typical example of electro-plating, Remeber i taught you to draw cathode on the left? For electro-plating, the object to be plated is on the cathode ( the negative electrode ) while the metal is on the anode ( positive electrode ). Obviously, the electrolyte must be the salt solution of the metal used for plating.
(6) D
reason: the question is trying to ask you what are the possible ions for conc LiCl. So there should be Li+, Cl- (from salt) and H+, OH- ( from water). Cations move towards cathode and anions move towards anode.
BUT, if the question asked about products, then LITHIUM is not discharged. Instead Hydrogen gas. Reason: Lithium is high up in the electro-chemical series as compared to hydrogen!
(7) C
reason: anions attracted to anode. So, no need to crack your brains thinking about the options. All the rest of the options are cations!
(8) B
reason: From the products, X and Y2, you can deduced it is a compound with the formula XY2.
(9)D
reason: Firstly, you need to choose 2 different metals from the reactivity series. And the electrolyte need to be aqueous ( ions ) or molten. But, Cu and Ag is quite a poor example. Why? Because these metals are not much further apart in the reactivity series. The voltage produced will not be larger enough.
(10) B
reason: ions discharged: H+ and Cl-. H+ discharge because Na+ is more difficult to be discharged due to electro-chemical series. Cl- is discharged due to 'concentration effect', so OH- ( from water ) is not discharged instead.
(11) D
reason: cathode gains mass due to copper from anode deposited onto it. Option C is rejected because electrode has weight, should not start from zero.
(12) B
reason: metal ions gain electrons at cathode while non-metal lose electrons at anode.
(13) A
reason: in aqueous copper (II) sulphate. Copper is below hydrogen in the electro-chemical series. So, copper ions will be discharged and copper will be deposited on to the cathode.
(14) B
reason: choose 2 different metals from the reactivity series. Question request for the greatest voltage.
(15) A
reason: (B)-anode is chlorine ( if concentrated; else is O2 ); cathode is hydrogen- NEVER sodium
(C):anode-hydrogen, cathode-sodium
(D):anode- bromine, cathode-lead
(16) A
reason: notice electrode X is connected to positive terminal, so electrode X is anode. Anions are attraced to anode. Cl- ions becomes Cl2 gas. Oxidised.
(17) A
reason: tricky question: the electrode is CARBON. this means all the ions involved are from the ELECTROLYTE. Cu2+ are attraced to cathode while OH- are attraced to anode. So, more of H+ is left behind. Hence solution becomes more acidic. If the question changes to COPPER electrode, then the concentration of CuSO4 and colour remains unchanged!
(18) C
reason: anions attracted to anode. SO42- is not discharged and OH- is discharged instead. This is the concept of 'Selective Discharge'.
(19) A
reason: (B) solution will become acidic. see question 17. For option C, Cl- will be discharged at the anode, H+ will be discharged at the cathode. So, the solution will have more OH- remaining. Hence, it will be alkaline. Option (D): due to the removal of water molecules [ cathode: hydrogen, anode: O2 ], so the concentration of sulfuric acid increases.
(20) B
reason: (A):how can cation forms negative ions. (D):R is below hydrogen, because if it is aqueous, then metal R ions will not be discharged.
(21) A
reason: electrons flow from anode (+) to cathode (-). so, cathode should be Y. Cathode is the more reactive metal.
(22) A
reason: for concentrated or dilute, sodium is NEVER discharged.
(23) C
reason: just focus at cathode-metal; anode-non metal. For option (A), it should be metal ions gaining electrons, and not giving electrons.
(24) B
reason: anode dissolves, all the Cu2+ ions are attracted to cathode hence metal is deposited. electrolyte remains unchanged. IF the electrode is NOT COPPER, example: carbon, then the blue colour of CuSO4 will fade away.
(25) B
'that's all folks!'
