Aqa chem4 15th june 2011 (resit) thread

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Yeah you still draw the reactive ammonium ion with the positive charge but you don't draw the bromine (or other halogen) as part of it. It's a reactive ion not a salt. You do then draw the attack which takes the hydrogen away to leave a primary/ secondary/ tertiary amine.

then why wasnt the ammonium ion acceptable as compound G in the Jan 011 paper

trailing bonds?

And I have a question concerning Carbon-13 nmr... in the spec it says "understand that Carbon 13 nmr gives a simpler spectrum than proton nmr"

How would we be asked to apply that knowledge? It just means that for C nmr there are no splitting patterns, right?

(edited 12 years ago)

Reply 383

Black Butler

Original post by adam1232

When you are drawing the repeating unit in a polymer are you supposed to include the two square brackets and n ?

NO. you will get penalised if you put the 'n' in. Square brackets are neutral.

Reply 384

bashx

Original post by FristyKino

3 easy for for a.i!!!
So first thing you do is using the data from experiment 1 and the rate equation you find the value of k.
So Rate=k[X]^2[Y]^0
So you can totally ignore y for now as it has a zero order.
So k=(2.68x10^-4)/[1.20x10^-3]^2
k=186.1

Now to find the missing blanks you just substitute values in the equation for all experiments - k will be constant in all the experiments.
I'll let you do the calculating for the 3 missing values now.

part a.ii. Well i've already done this for you above so its the same. But its units will be moldm^-3 s^-1

Yeah i found part aii easy! BUT you know how you worked out the second part before the first, is that the best way to go about it??
Ive worked them all out, but I cant seem to get EXP 4 answer? Please could you help me?

Reply 385

bashx

Original post by noobie93

It might ask like what is the advantage of 13C over proton nmr maybe?

Reply 386

jwest

are there any diprotic bases we need to be aware of? did a past paper earlier and failed to notice they were using h2so4 which messed up my buffer calculations?

Reply 387

bashx

Original post by jwest

are there any diprotic bases we need to be aware of? did a past paper earlier and failed to notice they were using h2so4 which messed up my buffer calculations?

yep same happened to me on that question!

Reply 388

Biologyman

Original post by jwest

are there any diprotic bases we need to be aware of? did a past paper earlier and failed to notice they were using h2so4 which messed up my buffer calculations?

I think it's just acids on the spec.

Reply 389

jwest

Original post by Biologyman

I think it's just acids on the spec.

cool to double check sulphuric acid is the only diprotic acid we need to worry about?

Reply 390

Zakir

When working out H+ for diprotic acids, do we multiply by 2 or divide by 2?

Reply 391

Potassium^2

I'd say this exam is harder than chem 5.
The most difficult thing for me is learning all of the conditions & reagents.
Looking to improve on 80ums from Jan so good luck everyone!!

Reply 392

JK471993

Original post by Biologyman

I think it's just acids on the spec.

... be able to perform calculations for the titrations of monoprotic and diprotic acids...

Reply 393

SashaLuLu

Original post by bashx

It might ask like what is the advantage of 13C over proton nmr maybe?

what are the advantages?

Reply 394

JK471993

Original post by Zakir

When working out H+ for diprotic acids, do we multiply by 2 or divide by 2?

Multiply by two.

Reply 395

Biologyman

Original post by jwest

cool to double check sulphuric acid is the only diprotic acid we need to worry about?

I'll have a check, I remember doing one earlier on a past paper but I'm not sure if it was just H2SO4 again but even so that's probably still the most common.

Original post by JK471993

Multiply by two.

If you're working out eg H2SO4 from pH you just divide by two.

(edited 12 years ago)

Reply 396

jwest

did the site just crash?

Reply 397

won-derer

does anyone have the jan 2011 past paper and mark scheme?

Reply 398

JK471993

Original post by Biologyman

I'll have a check, I remember doing one earlier on a past paper but I'm not sure if it was just H2SO4 again but even so that's probably still the most common.

If you're working out H+ from pH you divide by two.