… continued from here.
*SELF POWERS UP*
Finished In Front Of The Toilet
Exhausted from helping to prepare multiple answers to multiple papers (gosh this year’s exam timetables are really MEH 🙁 ), I once again slumped against my chair at The Temple in front of what is possibly the most beautiful, most ammonia (NH₃) pungent smell-free toilet you’ll ever find in any tuition centre in Singapore 😛
It’s been raining all morning, but thankfully the gloomy weather didn’t translate into doom and gloom in today’s O Level Chemistry MCQ paper.
The list of workings and explanations for each of the answers (where applicable) for the GCE O Level 2013 Chemistry Paper 1 MCQ have been compiled!
Latest versions:
- 1.2: Added further explanations to:
Q16 – Why Y is not oxidation due to unchanged oxidation state of elements in ethanoic acid.
Q32 – Why nitrogen does not undergo a reaction in the blast furnace.
Q36 – Note on cis-trans isomers *sigh* - 1.1: Q23 – corrected typo in explanation. Should be options A, B & C excluded.
Access here by clicking the 
button (if you haven’t yet done so).
Do they tally with yours? As usual, please, please leave a comment should you spot any mistake in the solution.
23 Comments
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For qn36 wikipedia answer is 4. For qn32 some people put nitrogen as well because of the high temperature. some people also put oxygen only.
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@anonymous: For Q36, Wikipedia's answer to the number of isomers involves the direction of the bonds and the bond angles which is not in syllabus, so it should not be considered and 3 isomers should be the right answer.
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Hi, for qn16 can it be y is oxidised as well, since the ethanoic acid lost hydrogen?
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@anonymous: For q16, y is not oxidation. The oxidation states of the elements do not change.
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@Bob: Oxidation is the lost of hydrogen actually. In fact if sodium metal is reacted with the ethanoic acid then sodium would indeed have its oxidation state increased by 1.
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@zzz: From The Temple's Alchemist:
"The most accurate and fail-safe way to determine whether a substance has oxidised or reduced is to compare the oxidation states rather than the loss/gain of oxygen and hydrogen.
In this case, the 'loss of hydrogen' does not necessarily mean that oxidation has taken place. The oxidation states of the elements in ethanoic acid remain the same even after reaction.
Also, sodium, if it had reacted with ethanoic acid, would have oxidised but not ethanoic acid which the diagram in the question is indicating."
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@zzz: Hi, I want to ask you qn 32. I believe that that the necessary gas blown into the bottom of the blast furnace is oxygen only and not other gases. This is because oxygen will then react with carbon to form carbon dioxide (highly exothermic reaction) which will then rises and reduced by carbon to form carbon monoxide. As such, carbon dioxide gas is actually formed in the blast furnace and not supplied from the bottom of the blast furnace. Moreover, the concentration of carbon dioxide in the air is only about 0.03% which can be considered negligible.
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Hi, I would like to know that what's the minimum MCQ score that one has to get to achieve an A1, based on past years experience.
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q16 should be Y and X. they asked for reaction that undergone oxidation, ethanoic acid + sodium. ethanoic acid loses one H. besides, Na increases its os from 0 to +1 to form the salt
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@a: See here.
Furthermore, the reactant in Y could be NaOH too, in which the oxidation state of Na in NaOH (+1) will not change when it forms sodium ethanoate (oxidation state of Na is +1 in CH3CO2Na)
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For qn 16, there is a loss in hydrogen. Isn't that an oxidizing reaction?
For qn 30, the experiment seems to be in an airtight condition so there cannot be presence of air right?
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@Anon: Q16: Please see here.
Q30: As copper oxide is reduced, oxygen is produced.
If it is airtight, no gas will be able to enter or leave the tube → coupled this with the buildup of oxygen + inflow of hydrogen and we may get a
KABOOOOOOOM
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Hi isn't the answer for question 12 A, and not D? I believe water molecules stay as molecules but do not form ions in an aqueous salt solution? Unless you're referring to electrolysis which isn't in this case?
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@Dan: From The Temple's Alchemist:
"Dissociation of water in aqueous solutions occurs irrespective of whether electrolysis has taken place.
As such, aqueous copper (II) chloride should have hydrogen and hydroxide ions on top of copper and chloride ions.
This applies Q27 as well."
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Hi, what do you think would be the minimum mark requirement for mcq to secure an A1?
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random, just giving my 2 cents worth, IMO the cis - trans is not that important and cambridge should not ask for it as O levels only include structural but not spatial or geometric isomerism
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For qn32, they said gases that go in from the bottom of the blast furnace. Doesn't that mean only oxygen reacts because carbon dioxide is only obtained when oxygen travels up the blast furnace and reacts with the coke?
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For question 36, the 4 isomers can actually be deduced just by drawing out. It does not have to be in syllabus but rather based on present knowledge, can be deduced. Answer should be c.
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@Anon: I don't think so. Check to see if you have any repeats in your drawings.
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@zzz: @zzz There are no mistakes, I'm sure. Do not forget that the c=c bonds can be a branch.
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@Anon: You mean you managed to deduce these two fellows based on O Level knowledge?
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Hi all, can you post your marks here? We can see the trend and difficulty level this time. I got 36.
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@anony what school are you from?