2012 O-Level Pure Chemistry Paper 2 Questions and Answers

ksosk

Finally, it is done!
Hope it can be of good help =)

Link:         scribd.com/doc/112319911

jsnleong

5ciii) Can i get 1m if say i just mention ammonium nitrate react with CaCO3 to give off ammonia gas which makes the soil infertile?

6bi) I totally forgot that bromine is liquid in r.t.p, so i went to assume that both are gas and state that they can be calculated by 24dm3/mol. However i did talk about volume as aspect of concern too. So 1m?

7ci) If i managed to give eqn, but did not balance it... so it will be 0?

8dii) They did not specify if its 19deg or 20deg.. so i put it as 18sec :O (value above 15sec)

How much do you think one should get /80 to secure A1?

Thks for ans!

ksosk

jsnleong 发表于 8-11-2012 11:11
5ciii) Can i get 1m if say i just mention ammonium nitrate react with CaCO3 to give off ammonia gas  ...

5c(iii) I would predict the marking scheme to include ammonia production due to reaction to be 1M, so yes you should get the 1M.

6b(i) Yes you should have the 1M again: 1M - suggest that density is based on mass/vol ratio
                                                               1M - explain why there's a difference in mass

7c(i) Based on common mark scheme, for 1M eqn writing, any mistakes in balancing or formula will result in zero mark.

8d(ii) I'm afraid the only answer accepted is 15s as the table clearly provides only one source of Fe3+ compound. The question before d(ii) also hinted that anion doesn't affect timing, plus magnesium nitrate vs magnesium chloride, albeit different temperature of 19 and 20 respectively, give rise to the same time taken of 46s! So, there shouldn't be an 18s =(


If I were to gauge the standard for Pure this year, I had to say that the marks allocation for the questions seem different this year and the toughest question happened to be the compulsory Q7 which is 12marks!
I would say the A1 comes from students who are able to handle Q7, thus resulting a range of around 70 for A1?
But again, there's no one that can give you a direct answer to the statistical range, so not to worry! I have seen too many students getting their A1 even when they felt that they fall below the range =)

jsnleong

Alright. Thanks a lot. Just one last thing, for qn 7, if say i give for 4 reasons for 7aii) which only worth 2m, if out of the 4, i got some incorrect ans, would they deduct marks? Or they would give me the full 2m as long i got 2 correct out of the 4 i gave?

ksosk

jsnleong 发表于 8-11-2012 16:26
Alright. Thanks a lot. Just one last thing, for qn 7, if say i give for 4 reasons for 7aii) which on ...

yes very likely marks will be deducted for overwriting

Rayner

Can the following answers be acceptable?
Q3Ai) Nitrogen react with Oxygen from the Air at high temperatures in the Internal Car Engines / The combustion of Nitrogen and Oxygen from the air at high temperatures in the internal car engines (Forget which one i wrote )
3aii) Lightning
5ciii) Calcuium Hydroxide with react with Ammonium sulphate to form Calcium Sulfate and Ammonia . Ammonia will be give off in the process and nitrogen wil be lost by the plast which is an essential plant element needed for plant growth
6cii) Need write Key? (Since both Chlorine)
6d)Draw the diagram got marks?
7aii) If you elaborate more is it ok? Like lesser energy = Save fossil fuels being burned as they are finite resources. (Even though i dont think got mark since only 2marks haha) , Dont get penalize can already.

ksosk

Rayner 发表于 8-11-2012 17:24
Can the following answers be acceptable?
Q3Ai) Nitrogen react with Oxygen from the Air at high temp ...

Q3Ai) Nitrogen react with Oxygen from the Air at high temperatures in the Internal Car Engines / The combustion of Nitrogen and Oxygen from the air at high temperatures in the internal car engines (Forget which one i wrote )
3aii) Lightning
5ciii) Calcuium Hydroxide with react with Ammonium sulphate to form Calcium Sulfate and Ammonia . Ammonia will be give off in the process and nitrogen wil be lost by the plast which is an essential plant element needed for plant growth
6cii) Need write Key? (Since both Chlorine)
6d)Draw the diagram got marks?
7aii) If you elaborate more is it ok? Like lesser energy = Save fossil fuels being burned as they are finite resources. (Even though i dont think got mark since only 2marks haha) , Dont get penalize can already.

For 3a(i) Both answers are acceptable (but you're rather freestyle-type) -- internal doesn't go
                   car engines! Still... you should have 2M

        3a(ii) Lightning-one word- is not accepted, although I may be stricter than actual Os.

          5c(iii)   2M-All keypoints are included.

          6c(ii)  If you are my student, 'key' is a MUST for all covalent bonding!

          6d) I expect the mark scheme to include marks for diagram so you should be safe... pray tell...

          7a(ii) You will get the marks if lesser energy comes with clear explanation like what you did =) Just a simple ' it uses lesser energy' will be zero.

Rayner

Haha ok thanks so much.

So ,6cii)No key= No marks / Depend on the leniency of the marker? Haha
7aii) Will have marks for saying that? They only give 2marks for that question .
9c) How are the marks given ? By explaining 2 different type of hyodrocarbon & their uses will there be a mark and explaining the demand of the it for the other mark?

Q7 this year was the toughest, If cant get the overall equation correct, its as good as losing 3marks (Cant continue the next part , even if you just find no. of mol for NaCl=1mark)

Approx how much is the overall Standard for a A2 in Percentage? (MCQ+PAPER2+SPA)

ksosk

Rayner 发表于 9-11-2012 10:08
Haha ok thanks so much.

So ,6cii)No key= No marks / Depend on the leniency of the marker? Haha

I thought when u said u elaborated meant there's one more point! Lesser energy with explanation itself is one point.

Q9c) The focus is to crack larger molecules of low demand into smaller useful molecules of high demand. One should get 1M for that answer. Stating an example is probably the other mark so ur use of the example ia unimportant but no marks should be deducted:)

I can't tell the range of A2 though but I can say that it will be the largest group so most of you will be A2.

Mind if I ask what school you're from?

Rayner

Got Physics One haha, Very tough paper