AQA CHEM2 ~ May 23rd 2012 ~ AS Chemistry

Does anyone know if there has been an examination question asking you to outline a nucleophilic substitution mechanism using ammonia?

I haven't seen one and I don't want to look through my last two papers yet as I'm planning to do them in exam conditions.

This was posted from The Student Room's iPhone/iPad App

Reply 982

eduardo1

Original post by Picture~Perfect

Here is a link to the paper in my skydive on hotmail
https://skydrive.live.com/?cid=518dbdd4f043877a#cid=518DBDD4F043877A&id=518DBDD4F043877A%21187

Here is the mark scheme
https://skydrive.live.com/?cid=518dbdd4f043877a#cid=518DBDD4F043877A&id=518DBDD4F043877A%21187

Thanks that's great, although I don't think that's the mark scheme

Reply 983

Jack_Smith

8

Original post by Picture~Perfect

Does anyone know if there has been an examination question asking you to outline a nucleophilic substitution mechanism using ammonia?

I haven't seen one and I don't want to look through my last two papers yet as I'm planning to do them in exam conditions.

This was posted from The Student Room's iPhone/iPad App

yep its definitely come up once!

Reply 984

YEH SAME, u hav give the URL for the same thing.. they are both for the 2012 QP, theres no mark scheme

Reply 985

Picture~Perfect, sorry i know thats not ur name... but i dont know ur name so.... nways plz attach mark scheme for 2012 ppr, uve attached QP twice!!

Reply 986

-Liberty

11

Can anyone help me with this.
Do you use concentrated sulphuric acid for aldehyde to carboxyllic? Because the textbook says that but I've seen it as aqueous in other places. What are you guys going to write?

Reply 987

Sorry about that I've put up the new link.

Reply 988

Original post by -Liberty

Can anyone help me with this.
Do you use concentrated sulphuric acid for aldehyde to carboxyllic? Because the textbook says that but I've seen it as aqueous in other places. What are you guys going to write?

When oxidising alcohols to aldehydes/keytones or an aldehyde to a carboxylic acid you use acidified potassium dichromate, which is the oxidising agent. To get an aldehyde you use a small amount of potassium dichromate acidified with dilute sulphuric acid and to get a carboxylic acid you use excess potassium dichromate acidified with concentrated sulphuric acid.
I Hope that helps clear things up. :smile:

Reply 989

username570224

11

Hey what's the equation for reaction of NaBr(s) with H2SO4? BOth stages, coz someone has altered it in my book...

I think first stage is NaBr+H2SO4->HBr+NaHSO4
Second stage in my book is 2H+ + 2Br- + H2SO4 -> SO2 + Br2 + 2H2O

Is that correct?

Reply 990

Original post by -Liberty

Can anyone help me with this.
Do you use concentrated sulphuric acid for aldehyde to carboxyllic? Because the textbook says that but I've seen it as aqueous in other places. What are you guys going to write?

Its acidified pottasium dichromate! and colour change is from orange-green (observation) :smile:

Reply 991

Original post by Picture~Perfect

Sorry about that I've put up the new link.

wheres the new link??

Reply 992

-Liberty

11

Original post by Picture~Perfect

When oxidising alcohols to aldehydes/keytones or an aldehyde to a carboxylic acid you use acidified potassium dichromate, which is the oxidising agent. To get an aldehyde you use a small amount of potassium dichromate acidified with dilute sulphuric acid and to get a carboxylic acid you use excess potassium dichromate acidified with concentrated sulphuric acid.
I Hope that helps clear things up. :smile:

So it's
alcohol --> aldehyde/ketone
postassium dichromate
dilute sulphuric acid
distillation

alcohol --> aldehyde ---> carboxyllic acid
potassium dichromate
reflux
heat
CONC sulphuric acid

Is this correct?

Reply 993

cheesecake11

2

do you guys have study leave?

Reply 994

Original post by Picture~Perfect

When oxidising alcohols to aldehydes/keytones or an aldehyde to a carboxylic acid you use acidified potassium dichromate, which is the oxidising agent. To get an aldehyde you use a small amount of potassium dichromate acidified with dilute sulphuric acid and to get a carboxylic acid you use excess potassium dichromate acidified with concentrated sulphuric acid.
I Hope that helps clear things up. :smile:

I'v never heard anything about adding H2so4, where did u lot get that from, :confused:

my teachers neva tol me.. and av checked my book again and all it says is...

Primary, secondary and tertiary alcohols can be distinguished by simple oxidation reactions using acidified potassium dichromate as an oxidising agent.!! :cool:

Reply 995

Original post by -Liberty

So it's
alcohol --> aldehyde/ketone
postassium dichromate
dilute sulphuric acid
distillation

alcohol --> aldehyde ---> carboxyllic acid
potassium dichromate
reflux
heat
CONC sulphuric acid

Is this correct?

S

i really dont get what u lot r onna bout!!

Reply 996

bogstandardname

5

HELP PLEASE

I am looking on the mark scheme for mechanisms and is says "max one mark for the use of sticks" what does this mean?

Reply 997

Ok... I have found this ... it has helped (sort of).

When you lot were talking about H2so4 did you mean the oxidising mixture can be made from potassium dichromate and sulphuric acid ?

anways this is what i am using..
its quite good.. u can print out and add in ur notes!!

http://www.pearsonschoolsandfecolleges.co.uk/FEAndVocational/Science/ALevelBiology/ASandA2OCRBiology/Samples/A2StretchandChallengeSamplePages/Sp_1_1_10.pdf

Reply 998

Original post by hus11128386

Ok... I have found this ... it has helped (sort of).

When you lot were talking about H2so4 did you mean the oxidising mixture can be made from potassium dichromate and sulphuric acid ?

anways this is what i am using..
its quite good.. u can print out and add in ur notes!!

http://www.pearsonschoolsandfecolleges.co.uk/FEAndVocational/Science/ALevelBiology/ASandA2OCRBiology/Samples/A2StretchandChallengeSamplePages/Sp_1_1_10.pdf

Yes, the oxidising agent is acidified potassium dichromate it is acidified with sulphuric acid.

Reply 999