Aqa chem4 15th june 2011 (resit) thread

Right so there's about two and a half weeks until this exam, hows everyone finding revision? (Because we all started weeks ago) :wink:

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Reply 1

Casshern1456

Yayyyyy I'm doing it :biggrin:

I need an a overall! Good luck everyone!!!
Acid-base and buffers are always a little tricky.

(edited 12 years ago)

Reply 2

lornaa

Original post by Casshern1456

Yayyyyy I'm doing it :biggrin:

I need an a overall! Good luck everyone!!!
Acid-base and buffers are always a little tricky.

Yeah! I'm pretty sure that's where I lost alot of my marks on the last paper there was just loads of it at the start!

Reply 3

Casshern1456

Original post by lornaa

Yeah! I'm pretty sure that's where I lost alot of my marks on the last paper there was just loads of it at the start!

I'm just going to have to work harder on the first 3 chapters I need a high UMS! :biggrin:

You know I don't even think Unit 4 is that hard really.

Reply 4

Assasingh

can any1 give me a link with all the chem4 papers? and chem5 if you could :smile:

Reply 5

lornaa

Original post by Casshern1456

I'm just going to have to work harder on the first 3 chapters I need a high UMS! :biggrin:

You know I don't even think Unit 4 is that hard really.

First three chapters?

Yeah I know, it seems a lot simpler now than it did in Jan. I do miss organic now we're doing chem 5 though :smile:

Reply 6

Arab_Empress

Original post by lornaa

Right so there's about two and a half weeks until this exam, hows everyone finding revision? (Because we all started weeks ago) :wink:

Hey Im doing the chem 4 resits in hope of getting a higher grade,
I was wondering if anyone can answer this, In rate equations the value of k constant of proportionality is only effected by temprature, however a catalyst increases the rate of reaction, and that doesnt alter the concentration of the reagents so theres nothing else in the equation that changes, so why doesnt k increase when a positive catalyst is added.

Reply 7

508836

I have revised up to aromatic chemistry...

-_-

This module is loooong.

Reply 8

JK471993

Need to get 76? in A2 Chemistry for an A. Definitely need an A in this unless I get an A in History (not gonna happen).

Chem 4 is okay compared to Chem 5 but I hope they don't ask us stuff from AS.

I find remembering reagents the hardest thing.

Reply 9

bashx

Im also resitting chem 4 but have only started reviing for it today :| major panic attack. does anybody have any useful revision notes on this??

Reply 10

bashx

Original post by JK471993

have you tried alevelchemistry? they have a really useful revision tool tohelp remmber the reagents. check it out and let me know what you think

Reply 11

duskflower

Same I only started today. The Collins Revision guide is pretty good! and also, there's this American freelance teacher on youtube who does reaally good chemistry videos, but you have to search by topic because their syllabus is a little different to ours.

I'll be posting revision notes for all the organic stuff in the next couple of days... xxx

Reply 12

JK471993

Original post by bashx

have you tried alevelchemistry? they have a really useful revision tool tohelp remmber the reagents. check it out and let me know what you think

Yh I used it last year as well. It's easily the best online Chemistry resource. The best thing is that it has plenty of exercises.

Reply 13

dolmio

I find this exam much easier than chem 5, dreading that one :frown:

how is everyone revising for chemistry? I generally just write notes but this is way too time-consuming!

Reply 14

jimmy303

Original post by Arab_Empress

Short Answer:
K does increase when a positive catalyst is introduced, you just don't need to know it for the exam, just that temperature increases it.

Long Answer:
K can be determined using the initial rate of reaction and the initial concentrations of reactants through rearrangement of the equation, as unit 4 teaches, or by using the Arrhenius equation which involves (amongst other things) the activation energy of the reaction and the temperature.

Thus by looking at the equation we can see that increasing the temperature or decreasing the activation energy (i.e. introducing a catalyst) results in an increase in the value of K.

(edited 12 years ago)

Reply 15

SashaLuLu

hey
i wondered if anybody could explain how to do question 5c on the june 2010 paper.

please quote me if you are able to help.
thanks

Reply 16

jimmy303

Original post by SashaLuLu

hey
i wondered if anybody could explain how to do question 5c on the june 2010 paper.

please quote me if you are able to help.
thanks

Calculate the pH of the solution formed when 25.0cm3 of 0.150 moldm–3 aqueous sulfuric acid are added to 30.0cm3 of 0.200 moldm–3 aqueous potassium hydroxide at 25 °C. Assume that the sulfuric acid is fully dissociated.

It wants you to give the pH of the solution after the two substances have reacted.

pH = -log[H+]

So we need to find the concentration of protons when the two solutions have reacted.

Find the initial number of moles of H+ (vol. x conc. x 2 as sulfuric acid is diprotic (two protons per molecule))
25/1000 x 0.15 x 2
= 7.5 x 10 to the power of minus 3 moles of H+.

find the initial moles of OH- (vol. x conc.)
30/1000 x 0.2
= 6 x 10 to the power of minus 3 moles of OH-.

Find out which is in excess (in this case the protons) and subtract the number of moles of the other substance from it. In essence the protons and hydroxide ions react to form water, leaving behind a certain number of moles of the substance in excess (in this case H+) which have nothing to react with.

So (7.5 x 10 to the power of minus 3) - (6 x 10 to the power of minus 3)
= 1.5 x 10 to the power of minus 3 moles of H+ left.

We then convert this to concentration.
Conc = moles / volume

The volume is the total volume after the reaction (i.e. the two solutions have been added together so the volumes are added together).
Volume in dm3 = (25 + 30) / 1000
= 0.055

Thus conc. = (1.5 x 10 to the power of minus 3) / 0.055
= 0.0273moldm-3 to three sig. fig.

-log(0.0273)
= 1.56

Hope this is helpful to you!

(edited 12 years ago)

Reply 17

508836

Original post by jimmy303

Well somebody's getting an A in this exam :colonhash:

Are you pretty much done with revision then?
Also how many exams do you have left?

Reply 18

jimmy303

Original post by T-Toe

I did the exam in Jan and got 120/120 ums, just got bored while browsing TSR :biggrin:

Just the one exam left, and thats unit 5 chem. Should probably be revising for it now if I'm honest :tongue:

And yourself?

(edited 12 years ago)

Reply 19

508836

Original post by jimmy303

I did the exam in Jan and got 120/120 ums, just got bored while browsing TSR :biggrin:

Just the one exam left, and thats unit 5 chem. Should probably be revising for it now if I'm honest :tongue:

You've got a while to study for chem5.

Wow, that's really good. I'm actually on my gap year and have decided to resit the whole of A-level chemistry in order to obtain an A/A* grade, I'm aiming for a high A in this paper, I need tips, how did you get 100%? How did you feel the exam went initially? Have you achieved high grades in all the other modules? What do you intend to study at university?
Sorry for all the questions, just curious thas all :biggrin:

I've completed unit 1 - it went okay, but I made such silly mistakes -_-. I do feel I smashed chem2 so hopefully it all weighs out.