Carbonyl compounds: Aldehydes and ketones

Question 1

What functional group do aldehydes and ketones belong to?

Answer 1

Carbonyl Compounds- C=O

Question 2

What is the difference between aldehydes and ketones?

Answer 2

Aldehydes- carbonyl group at the end of the chain and end in -al
Ketones- carbonyl group is in the middle of the chain and end with -one

Question 3

Which of aldehydes or ketones is oxidised when it reacts with an oxidising agent?

Answer 3

Oxidising agents react with aldehydes to form carboxylic acids whilst ketones aren’t easily oxidised

Question 4

What is tollens reagent and how can it be used to distinguish between aldehydes and ketones?

Answer 4

It is a colourless solution of silver nitrate dissolved within ammonia
1. When heated with an aldehyde, the Ag+ ions in the tollens reagent (AgNO3) are reduced to Ag to form a silver mirror
2. Ketones can’t be oxidised when heated with Tollens so there is no colour change

Question 5

What is Fehling’s solution and how can it be used to distinguish between aldehydes and ketones?

Answer 5

It is a blue solution containing Copper (II) ions dissolved in sodium hydroxide
1. When heated with an aldehyde the copper(II) ions are reduced to copper(I) to form a brick-red precipitate
2. Ketones don’t react with Fehling’s so no further reaction/ no precipitate

Question 6

What oxidising reagent is used to reduce aldehydes and ketones back into alcohols?

Answer 6

NaBH4, sodium tetrahydridoborate, dissolved in water with methanol, usually indicated by an [H]

Question 7

What is the mechanism for conversion of aldehydes and ketones back into alcohols? Draw it out

Answer 7

Nucleophilic addition as the H- acts as a nucleophile

Question 8

What are hydoxynitriles?

Answer 8

molecules with a CN and OH group

Question 9

Potassium cyanide with carbonyls, draw the mechanism

Answer 9

1. CM- attacks the partially positive carbon atom to donate a electron, both electrons from double bond are transferred to the oxygen
2. H+ ions added to the H group to form hydroxyl (OH)

Question 10

Why is potassium cyanide dangerous? Give 3 reasons

Answer 10

1. Irritant
2. dangerous when its ingested or inhaled
3. can react with moisture to form hydrogen cyanide, a toxic gas

Question 11

give 4 safety precautions to take during an experiment when handling potassium cyanide

Answer 11

1. Safety goggles
2. Lab coats
3. Wear gloves
4. Carry it out in a fume cupboard