3.3.8 Aldehydes and ketones

Question 1

What are primary alcohols oxidised to

Answer 1

Primary alcohols –> Aldehydes –> Carboxylic acids

Question 2

What are secondary alcohols oxidised to

Answer 2

Secondary alcohols –> Ketones

Question 3

Test(s) for Aldehydes

Answer 3

Tollens reagent - silver mirror
Fehlings solution - brick red ppt
Acidified potassium dichromate - orange to green solution

Question 4

What reduces aldehydes/ketones

Answer 4

NaBH4

Question 5

What are aldehydes and ketones reduced to

Answer 5

Aldehyde - Primary alcohol
Ketone - Secondary alcohol

Question 6

What type of reaction is the reduction of an alcohol/ketone

Answer 6

Nucleophilic addition

Question 7

How to produce hydroxynitriles from aldehydes/ketones

Answer 7

Nucleophilic addition
Using KCN
Add dilute acid

Question 8

Why use KCN instead of HCN (3)

Answer 8

HCN is a poisonous gas
HCN is hard to store
HCN is a weak acid and does not completely dissociate into CN- ions in water

Question 9

How to write reduction reaction

Answer 9

[H] instead of H2

Question 10

Explain why nucleophilic addition reactions of KCN, followed by dilute acid, can produce a mixture of enantiomers.

Answer 10

C=O bond is planar
So nucleophile can attack from above or below
With equal probability

Question 11

Nucleophiles for nucleophilic addition

Answer 11

H- or CN-