OCR B Salters - F335 Exam - 15 June 2011

OP

Original post by jungdao

It partially dissociates but when all the H+ reacts with the NaOH, more dissociates and it keeps happening until all the H+ have been used up. So, the fact that is a weak acid is irrelevant. :smile:

but isn't that like the point of the question... that the students assumption was wrong?

Reply 802

brendan.

12

Original post by tkoki1993

woohoo!!! someone else with 19.4!!!
the happiness has returned

:biggrin:

Ha! Lets just ignore everyone else's answer and remain in happiness.. until the mark scheme is released and then we can know for sure! :biggrin:

Reply 803

mooniibuggy

14

Oh no I made so many silly mistakes in this exam :frown:

Bye bye firm offer

Reply 804

brendan.

12

There were SO many calculation questions in this paper, it's becoming a blur. :frown:

Reply 805

OP

Original post by arsenalman

Im not 100% but a few other people got 7.44g on the thread. People who got 19g wasnt that on another mass question?

oh right..... all the calculation questions have become a bit of a blur to me. I cant really remember the paper that well. I just remember getting 19 for one question about mass and just assumed that was the question everyone is talking about

Reply 806

Original post by brendan.

There were SO many calculation questions in this paper, it's becoming a blur. :frown:

Thats the thing i like about chemistry because i do further maths it helps.

Reply 807

jungdao

Original post by tkoki1993

but isn't that like the point of the question... that the students assumption was wrong?

Yeah, so the student thought he would need less NaOH but he was wrong because he would still need it all. The fact that it's a weak acid doesn't affect the amount of NaOH needed for titration, which is the opposite of what he thought. :smile:

You'd probably get marks for talking about the acid dissociating more once the initial H+ is used up, and about equilibrium.

Reply 808

mooniibuggy

14

I remember getting 7.2 for one of the pH questions, that is all

Reply 809

OP

Original post by jungdao

Yeah, so the student thought he would need less NaOH but he was wrong because he would still need it all. The fact that it's a weak acid doesn't affect the amount of NaOH needed for titration, which is the opposite of what he thought. :smile:

You'd probably get marks for talking about the acid dissociating more once the initial H+ is used up, and about equilibrium.

so what was the actual answer???

Reply 810

limetang

19

Original post by brendan.

There were SO many calculation questions in this paper, it's becoming a blur. :frown:

Same. Just looking at people spurting numbers out. I can't decide whether or not I actually put that number down in a question or if I'm just subconsciously fooling myself into thinking I did to preserve my own sanity.

Reply 811

Original post by brendan.

Ha! Lets just ignore everyone else's answer and remain in happiness.. until the mark scheme is released and then we can know for sure! :biggrin:

This chemistry exam is the first exam ive been happy after this summer. My other exams ive done were S2 and unit 4 biology both by edexcel. I think edexcel have made all their exams harder or different from the past papers this summer or is it just me?

Reply 812

Original post by tkoki1993

so what was the actual answer???

There is no answer to these questions you just have to make it up :smile:

Reply 813

OP

Original post by arsenalman

This chemistry exam is the first exam ive been happy after this summer. My other exams ive done were S2 and unit 4 biology both by edexcel. I think edexcel have made all their exams harder or different from the past papers this summer or is it just me?

S2 was just a mind game

:mad:

Reply 814

jungdao

Original post by tkoki1993

so what was the actual answer???

The student was wrong because the strength of the acid doesn't affect how much NaOH is needed.

The acid partially dissociates and the H+ reacts with NaOH. Like with a buffer solution if [H+] decreases, the equilibrium will shift to the right and more acid will dissociate to bring the [H+] back up. This will keep happening until all the H+ have reacted with NaOH, so all the NaOH is needed.

Reply 815

OP

Original post by arsenalman

There is no answer to these questions you just have to make it up :smile:

so whats the point of the question!!! the joys of salters.....
:cool:

Reply 816

tom108

Can anyone remember the question to the 4 marker calculation at the end ?

Reply 817

04ayasin

Original post by limetang

Same. Just looking at people spurting numbers out. I can't decide whether or not I actually put that number down in a question or if I'm just subconsciously fooling myself into thinking I did to preserve my own sanity.

Exactly the same with me. Ive herd 7.4 so many times. Im not sure whether I actually wrote that down or whether I think I wrote it down because of all the times ive read it.

Reply 818

OP

Original post by jungdao

The student was wrong because the strength of the acid doesn't affect how much NaOH is needed.

The acid partially dissociates and the H+ reacts with NaOH. Like with a buffer solution if [H+] decreases, the equilibrium will shift to the right and more acid will dissociate to bring the [H+] back up. This will keep happening until all the H+ have reacted with NaOH, so all the NaOH is needed.

well that makes sense... how many marks was the question...
and while i'm talking about marks, anyone got THE PAPER?
please upload.... you'd get showered with pos rep if you do :biggrin:

Reply 819