AQA A2 CHEM4 & CHEM5 June 2015 [official discussion thread]

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benefits of acid anhydride vs acyl chlorde vs carboxylic acd >??????????

Original post by cedrico013

benefits of acid anhydride vs acyl chlorde vs carboxylic acd >??????????

anhydride do not produce corrosive hcl when reacting with nucleophile

Original post by cedrico013

benefits of acid anhydride vs acyl chlorde vs carboxylic acd >??????????

Acid anhydrides less vulnerable to hydrolysis less corrosive cheaper lessvolatile less dangerous to use

In ph calculations, will you get the full marks with a correct answer even if your methods do not match the method marks on the markscheme??

whats the hardest chem 4 paper iv done them all just want to go though the hardest. someone said it but i cant seem to find it

Jan 12?

Can someone explain half neautralisation point to me??

Original post by purplecloud

whats the hardest chem 4 paper iv done them all just want to go though the hardest. someone said it but i cant seem to find it

Look for the one with the lowest grade boundaries

Original post by purplecloud

whats the hardest chem 4 paper iv done them all just want to go though the hardest. someone said it but i cant seem to find it

Probs jan 2012

I think Jan 11 & June 11 is hardest papers up to now

What is the usual mark for an A and A*? Thought I'd ask here before searching through 5 years of boundaries.

Do amino acids undergo the same reactions as Carboxylic acids?

Original post by ThatPerson

What is the usual mark for an A and A*? Thought I'd ask here before searching through 5 years of boundaries.

Dont quote me on this but i think A will be over 84 marks

Original post by baffledchick

Do amino acids undergo the same reactions as Carboxylic acids?

Yes, well the carboxylic acid part will. Not sure about the amine part

Original post by ThatPerson

What is the usual mark for an A and A*? Thought I'd ask here before searching through 5 years of boundaries.

Luckily for you I've already done this in a moment of sadness a while ago :wink:

:wink:

I calculated the average marks for the 80%, 90%, and 100% UMS boundaries from all past papers since January 2010 for both CHEM4 and CHEM5.

CHEM4:
80% = 77 (HIGH: 81, LOW: 73)
90% = 86 (HIGH: 90, LOW: 83)
100% = 95 (HIGH: 99, LOW: 92)

CHEM5:
80% = 72 (HIGH: 74, LOW: 70)
90% = 81 (HIGH: 83, LOW: 78)
100% = 89 (HIGH: 92, LOW: 86)

(edited 8 years ago)

adorablegirl1202

when working out ph of a weak acid at half equivalence i know you look out for the volume of alkali to be half, do they both have to be same conc?

Original post by chem@uni

Reactions of Acid anhydrides anyone got al ist?

Theyre all the same pretty much as acyl chloride apart from instead of HCL you get a carboxylic acid

Original post by Doomlar

Luckily for you I've already done this in a moment of sadness a while ago :wink:

:wink:

I calculated the average marks for the 80%, 90%, and 100% UMS boundaries from all past papers since January 2010 for both CHEM4 and CHEM5.

CHEM4:
80% = 77 (HIGH: 81, LOW: 73)
90% = 86 (HIGH: 90, LOW: 83)
100% = 95 (HIGH: 99, LOW: 92)

CHEM5:
80% = 72 (HIGH: 74, LOW: 70)
90% = 81 (HIGH: 83, LOW: 78)
100% = 89 (HIGH: 92, LOW: 86)

Thanks! Guess I'll continue cramming :tongue:

:tongue:

The acid dissociation constant, Ka, for the weak acid HY has the value1.35 x 10–5 mol dm–3 at 25 °C.A buffer solution was prepared by dissolving 0.0236 mol of the salt NaY in 50.0 cm3 of a 0.428 mol dm–3 solution of the weak acid HY. Work out the pH.

This is from the Jan 2011 paper q2di.

My question us why don't you have to work out how many moles of the salt are in excess before working out the concentration of the salt?

christiannewong

When do you know when to use pka? Or work out excess moles?! Help!

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