AQA CHEM 2 June 2012 paper and unofficial mark scheme

OP

Original post by Mystic Creature

Think I got around 8 wrong. 10 wrong if the examiner's really mega harsh lol :redface:

Just wondering how many ums do you people think 92/100 will be..hopefully at least 130? :colondollar:

Got some stupid questions wrong..I didnt write acidified potassium dichromate for some reason!! :frown:

Well done

Should be around 130/135 UMS

Reply 181

LotsaJam

Original post by Bright.Inspiration.

Thank you!

I think I lost like 4 marks, how many ums could that be?

140. Duh :P

Reply 182

LotsaJam

Original post by Bright.Inspiration.

oh umm I actually think I lost 6 marks :s

So got like 94/100 I think
How many UMS would that be??

140.

Reply 183

LotsaJam

Original post by TanishaBellum

I reckon i got like 71/100?

Do you think that could be an A?

Easily. Some of them have been 67-70 for an A

Reply 184

el.sammo

3

hi, for the first two I put the lines as levelling off in the same place as the original but at different heights. Is this right or do they need to level off earlier than the original line? thanks

Reply 185

Original post by Picture~Perfect

x

Thanks for uploading. Can you tell me if any of these are valid alternatives:

Original post by Picture~Perfect

(a) steeper line, ending twice as high (2)
(b) less steep line, ending 2/5 as high (2)

How many marks would I get for each of these if I made the gradient change as appropriate, but forgot to change the final volume? 1 for each or zero?

Original post by knocker

(f) The HBr is not used up (1)

Could you have that it provides an alternative route for the reaction to take?

Original post by knocker

(ii) addition of water (1)

Would you gt marked down if you wrote 'breaking C=C bonds by adding water'? Would that be okay?

Original post by knocker

(c) CFC's - UV light breaks C-Cl bond, makes Cl. radicals
Cl. + O3 --> ClO. + O2
ClO. + O3 --> 2 O2 + Cl. chain reaction

Do you have to imply that it is a chain reaction or are the equations enough?

Original post by knocker

8(a) Safety - NaOH is corrosive, Environmental - Process 2 uses CO2 from local factory, less CO2 emissions/global warming (2)

For safety could you have that reflux was needed, therefore pressure would have built up a gases can't escape?

Original post by knocker

(ii) 2 I- --> I2 + 2e-
H2SO4 + 8 H+ + 8 e- --> H2S + 4 H2O

I know the question said half-equations, but since the way that equation is derived is by combining the two equations forming H2S and SO2 individually, could you have written those two equations individually instead of the half equations?

Original post by knocker

(iii) NaOH reacts with H+, equilibrium shifts right to make more H+ and opppose the change
bromine is used in small quantities

For the Le Chatelier bit, could you have put that NaOH increases the pH, so forward reaction is favoured to lower the pH again by making protons? For the 'Deduce' bit, could you say that the position of equilibrium is far to the right, therefore low concentration of Br2 at any given time?

Reply 186

knocker

Original post by Viva-La-Paradise 7

(ii) it contains no C-Cl bonds (1)

(i) H+ + Cl- --> HCl, HCl

CHCl3 does contain c-cl bonds :smile:

However element X is CCL4, which does not contain c-h bonds, so there is no peak at c-h.

KCI is solid. So i think the ionic equation is

H⁺ +KCl_s - HCl_g + K⁺_aq

H2SO4 is liquid too (not solution) as it's concentrated so using your argument it should be included always - I'm guessing you're thinking about spectator ions here?

Anyway if you remember from GCSE the simplest ionic equation for an "acid-base" reaction it is H+ + OH- --> H2O, ergo as this is also an acid-base reaction I still think, "H+ + Cl- --> HCl" is what they want but am not 100% certain.

Also the no C-Cl bond answer referred to a question that said something along the lines of why is some fluoroalkane compound not as bad for ozone as CFC's - the answer being that it has no C-Cl bonds to break with uv light and create Cl. to destroy O3.

Reply 187

knocker

Original post by extons

Indeed Emily! :tongue:

They accept just acidified at AS.

Maybe if it had been 2 marks then they might have wanted a named acid but in this case not.

Reply 188

Original post by LotsaJam

140. Duh :P

Original post by LotsaJam

140.

You seem pretty confident for low grade boundaries. Why is that? Last summer the UMS cap was 99/100, so it's very possible that 96/100 and 94/100 won't be full UMS.

Reply 189

Livourabi

It seemed to have been a bit of a tricky paper so who knows on grade boundaries. It's once been 71 for an A but mostly its 78/79. On the 78/79 paper, yeah it was 99/100 for full UMS. It'll still be high UMS tho!!

Reply 190

Livourabi

I THINK I got in like the 87-90 area. Hopefully that's decent UMS!

Reply 191

Praami

what would the grade boundaries for this paper be like? any estimation????

Reply 192

erniiee

13

Original post by knocker

They accept just acidified at AS.

Maybe if it had been 2 marks then they might have wanted a named acid but in this case not.

Are you intentionally ignoring my quotes?

Reply 193

OP

Original post by When you see it...

Thanks for uploading. Can you tell me if any of these are valid alternatives:

How many marks would I get for each of these if I made the gradient change as appropriate, but forgot to change the final volume? 1 for each or zero?

Could you have that it provides an alternative route for the reaction to take?

Would you gt marked down if you wrote 'breaking C=C bonds by adding water'? Would that be okay?

Do you have to imply that it is a chain reaction or are the equations enough?

For safety could you have that reflux was needed, therefore pressure would have built up a gases can't escape?

I know the question said half-equations, but since the way that equation is derived is by combining the two equations forming H2S and SO2 individually, could you have written those two equations individually instead of the half equations?

For the Le Chatelier bit, could you have put that NaOH increases the pH, so forward reaction is favoured to lower the pH again by making protons? For the 'Deduce' bit, could you say that the position of equilibrium is far to the right, therefore low concentration of Br2 at any given time?

1. I'm assuming its one mark for the gradient change and one mark for the volume change, so you would get one for each in this case.

2. No as it asks why this species has to be the catalyst and the trait of a catalyst is that it is not used up in a reaction

3. Possibly as you mention the addition of water

4. The equations are worth three marks and the question is worth four, you need some sort of written explanation as the question asks you to explain with the aid of equations why CFC's are banned.

5. I'm not sure on this one, but any sensible safety measure should be credited.

6. No, it asks for had equations, you needed to have given half equations.

7. That sounds reasonable and you've stated that equilibrium will shift right, so I don't see why you wouldn't get marks here.

I hope this helps clear some things up for you.

Reply 194

knocker

Original post by erniiee

Are you intentionally ignoring my quotes?

??? You mean you're question about grade boundaries? I don't have a clue, it seemed like a fairly standard paper to be honest, with one or two little niggly bits.

And as for the high pressures? I doubt that would get any credit for that particular question where does it mention they use a high pressure?

(edited 11 years ago)

Reply 195

Original post by Picture~Perfect

1. I'm assuming its one mark for the gradient change and one mark for the volume change, so you would get one for each in this case.

2. No as it asks why this species has to be the catalyst and the trait of a catalyst is that it is not used up in a reaction

3. Possibly as you mention the addition of water

4. The equations are worth three marks and the question is worth four, you need some sort of written explanation as the question asks you to explain with the aid of equations why CFC's are banned.

5. I'm not sure on this one, but any sensible safety measure should be credited.

6. No, it asks for had equations, you needed to have given half equations.

7. That sounds reasonable and you've stated that equilibrium will shift right, so I don't see why you wouldn't get marks here.

I hope this helps clear some things up for you.

Thanks very much. I honestly had no idea about the catalyst definition - I thought you could have put either.
Do you know what the grade boundaries will be like? I thought it was a pretty fair paper but unfortunately I made a fair few mistakes.

Reply 196

OP

I've looked through again and I'm giving myself 76, I really hope thats enough..

Reply 197

Original post by Picture~Perfect

1. I'm assuming its one mark for the gradient change and one mark for the volume change, so you would get one for each in this case.

2. No as it asks why this species has to be the catalyst and the trait of a catalyst is that it is not used up in a reaction

3. Possibly as you mention the addition of water

4. The equations are worth three marks and the question is worth four, you need some sort of written explanation as the question asks you to explain with the aid of equations why CFC's are banned.

5. I'm not sure on this one, but any sensible safety measure should be credited.

6. No, it asks for had equations, you needed to have given half equations.

7. That sounds reasonable and you've stated that equilibrium will shift right, so I don't see why you wouldn't get marks here.

I hope this helps clear some things up for you.

BTW for the EU banning CFC one I put as a conclusion - 'it therefore breaks down ozone, which protects us from UV radiation'. Would that get the written explanation mark or have I got the wrong end of the stick with regards to why it is bad?

Reply 198

OP

Original post by When you see it...

Thanks very much. I honestly had no idea about the catalyst definition - I thought you could have put either.
Do you know what the grade boundaries will be like? I thought it was a pretty fair paper but unfortunately I made a fair few mistakes.

It's hard to say, the boundaries aren't set until after the exam so it depends on how hard/easy people found the paper.

The average of the last four papers is:
A: 74
B: 66
C: 57

(edited 11 years ago)

Reply 199