Aqa chem 4/ chem 5 june 2016 thread

http://filestore.aqa.org.uk/subjects/AQA-CHM4-W-QP-JUN08.PDF

Can someone help me with q1di?

So the 5 peaks on the M/Z are
Carbon-12
Hydrogen-1
Oxygen-16
Chlorine-35
Chlorine-37

And then the for the most abundant peak
1) get an average abundance for Cl-35 and Cl-37

So (37x25+35x75)/100

Which gives you 35.5

2)most abundant peak is the molecular ion
So basically add up the Mr

12*12 + 1*4 + 2*16 + 4*35.5 = 322.0



Posted from TSR Mobile

Yeah exactly. So if you were to add, say, HCl instead of NaOH, then there is more H+ ions in the equilibrium that need to be used, so the equilibrium shifts to the left (to use up H+) so there is less Y- and more HY, so you take the moles of HCl from Y- and you add them to HY, then put the new moles into Kc blah blah blah, does that make sense? Tbf it's pretty confusing but you've just got to think about it in terms of what's happening to the equilibrium


Posted from TSR Mobile

your explanation for part a is wrong. its the configurations of Cl 35 and Cl 37

Peak 1: all 4 Cls are 35
peak 2: 3 Cls are 35 and 1 is Cl 37
peak 3: 2 Cls are 35 and 2 Cls are 37
etc.

so 5 different peaks

yh sort of I will look into it a bit later,

Do you mind helping me with 4ei and 4eii.
I thought NaOH causes the amino acid to be split up again.
And Im not sure what ethanoyl chloride dos

It stays at 4.20. Water only partially dissociates and very weakly at that. Therefore it only changes pH by +- 0.01 if that. mostly, doesn't change pH

NaOH is a strong base, which functional group of the amino acid will react with the base?

For the reaction with Ethanoyl Chloride, what part of the amino acid will act as a nucleophile?

I find it helps to write out the actual chemical equations so you can see what's going on


Posted from TSR Mobile

Im not sure sorry

What year is this question from?

Yeah. You're looking at how much excess there is after neutralisation. If it's a strong acid then you have to multiply by 2 because it will fully dissociate and 2H+ is available for neutralisation.

Can anyone think of anything from AS we need to go over? Like do we need to know like the UV thingy and shapes and stuff like that?


Posted from TSR Mobile

im so confused you've bypassed my question and contradicted yourself so many times

NaOH is a strong base, which functional group of the amino acid will react with the base?

For the reaction with Ethanoyl Chloride, what part of the amino acid will act as a nucleophile?

Bases react with acids in a neutralisation reaction, an amino acid has a carboxylic acid group.

The reaction with ethanoyl chloride is the exact same as any nucleophile attacking the electron-deficient carbon. Reaction between ammonia and ethanoyl chloride? Just so happens that an amino acid has the N with a lone pair that will react in the same way.

hmm ok but it seems quite complicated to draw?

Reacts with COOH - weak acid strong base

B.) the NH2 - it's a nucleophilic addition elimination mechanism

I wrote the mechanism out if it helps you imagine it

OOPs; just realised i didn't do the other COOH group, but that would be the same too! Sorry

Eh not really. Look at the post above yours.