AQA CHEM4 ~ 14th January 2013 ~ A2 Chemistry

Okay, so I'd like a little help, see if I'm missing anything. Distinguishing between functional groups and how to identify them.

Aldehyde - Tollens reagent - Silver mirror formed
Carboxylic acid - Na2CO3 - Effervescence of CO2
Alkene - Bromine water - Brown to colourless
Ester - Na2CO3 - Effervescence of CO2 (is this right?)
Acyl chloride - NaHCO3 - Effervescence of CO2 (???)
Alcohol - K2Cr2O7 - Orange to Green

Do I need to know anymore? can't really think properly it is late but correct me above if I'm wrong and add some on if i missed them out, thanksss.

Acyl Chloride test is to add AgNO3, gives vigorous reaction and a white ppt.

Original post by Boom533

Can anyone help with the reagents and conditions of nitrile -> amide and amide -> nitrile? Or do we not need this?

Also amine -> amide is just react with carboxylic acid right?

Don't need to know all of this.

Nitrile -> Amine, is LiAlH4. Or H2 / Ni

(edited 11 years ago)

Reply 1381

lewis7

8

Original post by Me-A-Doctor?

Acyl Chloride test is to add AgNO3, gives vigorous reaction and a white ppt.

Don't need to know all of this.

Nitrile -> Amine, is NaBH4.

Ah alright, cheers.

Reply 1382

username890104

2

Original post by Me-A-Doctor?

Nitrile -> Amine, is NaBH4.

It isn't. You're best off using H₂/Ni, but if you're going to use something else then use LiAlH₄. NaBH₄ hasn't got the muscle to reduce a nitrile to an amine.

Reply 1383

username890104

2

Original post by lewis7

Alright thank yous. Have yous already took this exam or 1st time?

First time.

Reply 1384

Me-A-Doctor?

Original post by Tullia

It isn't. You're best off using H₂/Ni, but if you're going to use something else then use LiAlH₄. NaBH₄ hasn't got the muscle to reduce a nitrile to an amine.

Sugar. I was thinking LiALH4 then wrote NaBH4. My Bad, NaBH4 is for Aldehyde/Ketone -> Alcohol.

Original post by lewis7

Ah alright, cheers.

Apologies, I was wrong. I have revised my answer :smile:

(edited 11 years ago)

Reply 1385

Dirtybit

20

Original post by lewis7

Okay, so I'd like a little help, see if I'm missing anything. Distinguishing between functional groups and how to identify them.

Aldehyde - Tollens reagent - Silver mirror formed
Carboxylic acid - Na2CO3 - Effervescence of CO2
Alkene - Bromine water - Brown to colourless
Ester - Na2CO3 - Effervescence of CO2 (is this right?)
Acyl chloride - NaHCO3 - Effervescence of CO2 (???)
Alcohol - K2Cr2O7 - Orange to Green

Do I need to know anymore? can't really think properly it is late but correct me above if I'm wrong and add some on if i missed them out, thanksss.

Acyl chloride test: Warm with water and hcl fumes are given off (Check this with litmus paper as it turns red)

Reply 1386

SamEastie

2

does anyone know any uses/applications of buffer solutions?

Reply 1387

Me-A-Doctor?

Original post by SamEastie

does anyone know any uses/applications of buffer solutions?

Blood is the most obvious buffer solution. The sea is also a buffer solution. Then shampoo, to stop it hurting your eyes!

Reply 1388

SamEastie

2

Original post by Me-A-Doctor?

Blood is the most obvious buffer solution. The sea is also a buffer solution. Then shampoo, to stop it hurting your eyes!

yeah i knew blood but it didnt seem like a use of a buffer :') shampoo yess good call. thanks.

Reply 1389

lewis7

8

Original post by Dirtybit

Acyl chloride test: Warm with water and hcl fumes are given off (Check this with litmus paper as it turns red)

So there is two tests for an acyl chloride? AgNO3 to give white precipitate of AgCl.
Aswell as the one you have just stated, which one do examiners prefer haha?

Reply 1390

Dirtybit

20

Original post by lewis7

So there is two tests for an acyl chloride? AgNO3 to give white precipitate of AgCl.
Aswell as the one you have just stated, which one do examiners prefer haha?

yup, it depends on the other compound which they ask you to give a test for acyl chloride really, I tend to use the one I said when they also put ethanoyl chloride and ask to distinguish between the two :biggrin:

Meant to say Ethanoic anhydride

(edited 11 years ago)

Reply 1391

lewis7

8

Original post by Dirtybit

yup, it depends on the other compound which they ask you to give a test for acyl chloride really, I tend to use the one I said when they also put ethanoyl chloride and ask to distinguish between the two :biggrin:

okay nice one.

Reply 1392

Me-A-Doctor?

Original post by lewis7

So there is two tests for an acyl chloride? AgNO3 to give white precipitate of AgCl.
Aswell as the one you have just stated, which one do examiners prefer haha?

I wasn't aware of the other, and have always put what I said, but I'm sure the other is correct!

Question Time.

As a side, I find a good way to revise organic synthesis is to try to go from one compound to another.

So here's a question if anyone wants to have a go, I posted one of these before and a couple of people bothered :wink:

Propyl Chloride ---> Trimethylbutylammonium ion. [This is R4N+] if you weren't sure.

I used 8 steps I think, however may be able to use less.

Reply 1393

Mocking_bird

11

Just had a suprise mock... pretty sure I did terrible, i'm so bad at this unit 4 :frown:

Reply 1394

Mocking_bird

11

Original post by Me-A-Doctor?

I wasn't aware of the other, and have always put what I said, but I'm sure the other is correct!

Question Time.

As a side, I find a good way to revise organic synthesis is to try to go from one compound to another.

So here's a question if anyone wants to have a go, I posted one of these before and a couple of people bothered :wink:

Propyl Chloride ---> Trimethylbutylammonium ion. [This is R4N+] if you weren't sure.

I used 8 steps I think, however may be able to use less.

Hmm..

Propyl chloride -> propanoic acid -> propanal -> propanol -> propene -> Here i'm a bit confused as from the general route i learnt i would go to a haloalkane and then quarternary ammonium salt but im a little confused now :smile:

... will it involve a cyanide ion somewhere as its going from prop to bute?

(edited 11 years ago)

Reply 1395

SamEastie

2

how do you convert a carbonyl to a hydroxynitrile? is that using KCN and dilute H2SO4? but i dont get how its done, i thought it was HCN...

Reply 1396

SDavis123

15

Original post by SamEastie

how do you convert a carbonyl to a hydroxynitrile? is that using KCN and dilute H2SO4? but i dont get how its done, i thought it was HCN...

What's the actual question?

And KCN and HCN are used for different reactions. KCN is used for either nucleophilic substitution or elimination and HCN is used for nucleophilic addition.

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

Reply 1397

Sorro10

OP

5

I think I'm confusing myself, how is the rate in Question 1(ii) in this question 2? The initial concentration of B doubles from Experiment 1->3, the initial rate increases by x16. I've just confused myself so much on an easy question.

http://www.a-levelchemistry.co.uk/aqa%20a2%20chemistry/Unit%204%20Past%20Papers%20and%20Revision%20Aids/Unit%204%20Jan%202002%20ms.pdf

From what I remember:

0 order: If [A] doubles, rate stays same, if [A] triples, rate stays same.
1 order: If [A] doubles, rate also doubles, if [A] triples, rate also triples.
2 order: If [A] doubles, the rate is 2²=4 times faster, if [A] triples, rate will be 3²=9 times faster.

(edited 11 years ago)

Reply 1398

SamEastie

2

Original post by SDavis123

What's the actual question?

And KCN and HCN are used for different reactions. KCN is used for either nucleophilic substitution or elimination and HCN is used for nucleophilic addition.

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

well in my notes it says its done using HCN for nucleophilic addition, but then it says you use H2SO4 and KCN? :s-smilie:

Reply 1399

SDavis123

15

Original post by SamEastie

well in my notes it says its done using HCN for nucleophilic addition, but then it says you use H2SO4 and KCN? :s-smilie:

I'm not 100% sure but I'm thinking that:

1. When you react with HCN first you're going to get an alcohol group and a CN group
2. (This is where I'm unsure) H2SO4 reacts through electrophilic addition so it 'should' go for the triple bond in the CN group but I'm not sure exactly what happens here...

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

AQA CHEM4 ~ 14th January 2013 ~ A2 Chemistry

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