Edexcel Chemistry Unit 5 June 19 2012

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in the empirical formulae thingy i didnot bother amount N much ! cuz the volume was given so from V=moles * 24000 i got the moles as 0.001 mole ! so i directly used that in empirical formulae thingy where you have to find mole ratios and stuff ! i didnt use it for % thingy cuz nitrogen isnt involved in that right !
it was COMBUSTION ANALYSIS and only oxygen hydrogen and carbon is involved in it !

Reply 981

NutterFrutter

Original post by alz333

shouldnt they give one mark cause i got 90% of the equation correct don't you just feel so annoyed with yourself when you make school boy errors like that

I know right. Such an easy question and I manage to mess it up. :mad:

Reply 982

alz333

Original post by zincoff

The mass of nitrogen is 24/24000*(2x14) because it exists as a diatomic molecule, so unfortunately what you wrote isn't correct.

as far as i can think that would be a bit harsh seeing as though they should have mentioned molecule of nitrogen, yet oxygen is also diatomic but if you were to calculate the mass in the question yoou would multipl,y *16

Reply 983

NutterFrutter

Original post by zincoff

I can't remember this question- where was it?!?

Section B somewhere.

Reply 984

iesians

Original post by Kasarna

I said three since there was a carbon in the benzene ring thing to the right that had a hydrogen.

2 for the Ch3 groups and maybe one more for that carbon...though am not entirely sure.

why 3 ??! H in ch3 group is in the same environment ! so it would show 1 peak !
and then 1 mmore peak for the CH .

Reply 985

NutterFrutter

Original post by alz333

You have already calculated the mass of carbon atoms and hydrogen atoms so the rest of the mass is oxygen atoms.

Reply 986

iesians

what was the answer for the MCQ in which Naoh and DNPH and HCl were being added to a compund ??
i chose all three would react !!!!

Reply 987

F1's Finest

someone needs to upload the paper.

This paper should be enough for my A overall....

Reply 988

NutterFrutter

Original post by iesians

what was the answer for the MCQ in which Naoh and DNPH and HCl were being added to a compund ??
i chose all three would react !!!!

I put only HCl and NaOH. There was no ketone/aldehyde group, it was an ester group.

Reply 989

Kasarna

Original post by iesians

why 3 ??! H in ch3 group is in the same environment ! so it would show 1 peak !
and then 1 mmore peak for the CH .

What I thought the ch3 groups were in fairly different environments around that ring therefore 2 coupled with the ch giving three. FML might have lost a mark then...

Reply 990

iesians

Original post by NutterFrutter

I put only HCl and NaOH. There was no ketone/aldehyde group, it was an ester group.

but even ester contains a CARBONYL GROUP right ?! im dead.

Reply 991

Augmented hippo

Original post by alz333

how comes alot of people got molar mass 134 with c4h804N
because mass of nitrogen 24/24000 *14 will give you the mass and then divide that by the total mass to get the % composition
For carbon mass 12/44 * mass of c02 they gave
percentage % mass of carbon/total mass
mass of hydrogen 2/18 * mass of water
then percentage of hydrogen mass of hydrogen/total mass
the rest of the percentage was oxygen
then if you calculate the mole for each divide by the smallest number you get c4h804N
I hope so this is correct as i did check it many times

When you worked out the moles of nitrogen you forgot it is diatomic so you have to multiply it by 2 to get the number of moles of single N atoms. This will then change your value for moles of oxygen so you end up with C4H8N203

Reply 992

EffKayy

Empirical formula :frown:

FML.

Funny thing was when I looked around the room most people were also on that question for ages.

I multiplied the moles of nitrogen by 14, not 28.
Will they give follow through marks? ffs.

Reply 993

zincoff

Original post by NutterFrutter

I put only HCl and NaOH. There was no ketone/aldehyde group, it was an ester group.

Do you remember what molecule it was?
I remember putting 'only HCl' but I can't remember why I discounted NaOH

EDIT:
wait nevermind...just realized fml.

Reply 994

iesians

Original post by Kasarna

What I thought the ch3 groups were in fairly different environments around that ring therefore 2 coupled with the ch giving three. FML might have lost a mark then...

you only have to see in which environment H is ! not CH3 ! cuz its NMR which only resonates H atoms ! so as long as they are in CH3 they are in the same environment.

Reply 995

alz333

can anyone put the answers up for all mcq questions

Reply 996

iesians

what was the reagent for the diphenyl thingy ??!
i drew a benzene ring with CH2Cl group attached to it ?!

Reply 997

NutterFrutter

Original post by zincoff

Do you remember what molecule it was?
I remember putting 'only HCl' but I can't remember why I discounted NaOH

EDIT:
wait nevermind...just realized fml.

I can't remember myself but I remember being tempted to put all 3.

Reply 998

zincoff

Original post by NutterFrutter

I can't remember myself but I remember being tempted to put all 3.

It was an ester so it reacts with acid and base hydrolysis.

Reply 999

monsterdeeX

for the peaks question I got 1, because all the CH3 groups were in the same environment as I saw it, and it would be one peak, and the height will be multiplied by 3? ... please correct me if i'm wrong?!