Edexcel A2 Chemistry Exams -6CH04 (14th June) and 6CH05 (22nd June) Discussion Thread

https://c838cff4741acb48ae1ed62e59927ff4c2073557.googledrive.com/host/0B1ZiqBksUHNYbVpyRTRJN1lFS00/January%202014%20(IAL)%20QP%20-%20Unit%204%20Edexcel%20Chemistry.pdf

Q19)b)v) i dont get how its hazardous due to being in powder form?

(v) Icing sugar can be hazardous when it is being finely powdered in a factory. Explain why sucrose is stable at room temperature, in spite of your answer topart (iii), but its manufacture is hazardous.

MS: (hazardous because small particles/ powder have/ has)larger surface area and react faster

Reply 722

mizzyportia

10

Can someone explain the advantages and disadvantages of biofuels and biodiesel :colondollar:

Reply 723

Original post by maria17xo

I am really stuck on this one marker question, i have tried but can't seem to get the right answer. can someone please explain it. it is question 3d on multiple choice. Thanks

http://qualifications.pearson.com/content/dam/pdf/A%20Level/Chemistry/2013/Exam%20materials/6CH04_01R_que_20130612.pdf

This question really got me too haha. If you work out the moles of the acid and alkali, you'll find that the acid is in excess. When you subtract the moles of alkali from the moles of acid to see how many moles of acid you have left over, you'll find that it is the same as the moles of ethanoate ions formed. Thus, [HA] = [A-], which means that Ka = [H+] (think about the expression for Ka and you'll see why this is the case). So, to find [H+], you just use your value for Ka!

Reply 724

ihaspotato

can anyone give a links to Jan 16 U4 paper? MS+QP?

Reply 725

tootfruity

11

Original post by ihaspotato

I'm not sure if NH4Cl to NH3 + HCl counts as dissociating....does it?

I thought dissociating meant to make H+ or OH- ions straight away then if possible make more eg. H+ from the same compound... now I'm confused. :s-smilie:

Hmm maybe you're right :s-smilie:

I don't know :/ I would say that the question is probably elimination:
We know ammonia is a weak base so it will have the highest pH (most alkaline) and then carboxylic acids are weakly acidic so that leaves NH4Cl so be left as the most acidic?!

Reply 726

January 2016 (IAL) QP - Unit 4 Edexcel Chemistry.pdf528.4KB

Original post by imnoteinstein

https://c838cff4741acb48ae1ed62e59927ff4c2073557.googledrive.com/host/0B1ZiqBksUHNYbVpyRTRJN1lFS00/January%202014%20(IAL)%20QP%20-%20Unit%204%20Edexcel%20Chemistry.pdf

Q19)b)v) i dont get how its hazardous due to being in powder form?

(v) Icing sugar can be hazardous when it is being finely powdered in a factory. Explain why sucrose is stable at room temperature, in spite of your answer topart (iii), but its manufacture is hazardous.

MS: (hazardous because small particles/ powder have/ has)larger surface area and react faster

Do you not get what the mark scheme is saying? In case you don't, larger surface area = increase in collision frequency hence increase in rate of reaction.

Reply 727

Aimen.

7

Original post by TeaAndTextbooks

Does anyone know where I can find Jan 16 IAL Chem4? Thanks

Posted from TSR Mobile

Incase you didn't find it yet! I know it's too late lol

January 2016 (IAL) MS - Unit 4 Edexcel Chemistry.pdf344.6KB

WCH04_01_pef_20160303.pdf100.0KB

Reply 728

Original post by n2697

and this one! Thanks in advance

Step 1: Work out moles of HCl.

Step 2: Work out concentration of [H+] (which will be equal to [HCl] since HCl dissociates fully, being a strong acid) once added to the solution using the formula concentration = moles * 1000 / volume.

Step 3: -log([H+]) = pH :smile:

Reply 729

imnoteinstein

Original post by Don Pedro K.

Do you not get what the mark scheme is saying? In case you don't, larger surface area = increase in collision frequency hence increase in rate of reaction.

okay im probably being dumb af: I get that the rate increases bc large surface area. Whats the hazard though? Why is that dangerous?

Reply 730

Original post by n2697

help d:

3:1 molar ratio so concentration will be in a 3:1 molar ratio since they are all in the same volume.

Thus:
Ka = [H+][CH3COO-] / [CH3COOH]

Rearranging...

[H+] = Ka * [CH3COOH] / [CH3COO-]

[H+] = (1.7x10-5)(3)/(1) =====> [H+] = 5.1x10-5 moldm-3.

Therefore, pH = -log(5.1x10-5) = 4.29.... = 4.3 to 1 decimal place :smile:

Reply 731

Original post by imnoteinstein

okay im probably being dumb af: I get that the rate increases bc large surface area. Whats the hazard though? Why is that dangerous?

Haha no dw I think I would have had to have done the previous parts, because that probably gives a clue.Not sure sorry :s

(edited 7 years ago)

Reply 732

_H_V

4

Original post by maria17xo

I am really stuck on this one marker question, i have tried but can't seem to get the right answer. can someone please explain it. it is question 3d on multiple choice. Thanks

http://qualifications.pearson.com/content/dam/pdf/A%20Level/Chemistry/2013/Exam%20materials/6CH04_01R_que_20130612.pdf

This a buffer question (as theres a weak acid involved) so you have to work out how much salt if form from the neutralisation and then work out the left over amount of ethanoic acid, use these values in the Ka equation for buffers and the answer is D

Reply 733

ayvaak

Could someone please explain why there are different answers to similar questions?

Reply 734

sonam_28

1

how many peaks are there in a low resolution nmr spectrum for pentanal

Reply 735

Somebody tell me why it's not B?

@Funky_Giraffe @samb1234

(edited 7 years ago)

Reply 736

_H_V

4

Original post by imnoteinstein

okay im probably being dumb af: I get that the rate increases bc large surface area. Whats the hazard though? Why is that dangerous?

The question is talking about the combustion of sucrose, its dangerous because finely powdered sugar (sucrose) can ignite because of the increased rate of reaction. Having the sugar ignite into flames is pretty dangerous :tongue:

Reply 737

_H_V

4

Original post by sonam_28

how many peaks are there in a low resolution nmr spectrum for pentanal

5 peaks

Reply 738

MacroniCheese