Unit 4.4 Aldehyde and ketones

Question 1

What is a carbonyl group?

Answer 1

It’s a functional group found in compounds such as aldehydes, ketones and carboxylic acids. (C=O)

Question 2

Give the structural formula for propanal.

Answer 2

Question 3

Give the structural formula for propanone.

Answer 3

Question 4

Describe how a ketone or an aldehyde can be found.

Answer 4

• Use Tollen’s reagent
• Use AgNO3/NH3 as an oxidisng agent
• The Ag (I) ions are reduced to metallic silver (Ag⁺ + e^- -> Ag) when an aldehyde is oxidised into a carboxylic acid.

Question 5

What is an aldehyde group?

Answer 5

Contains the CHO functional group. These can be oxidised into carboxylic acids by heating them under reflux with potassium dichromate.

Question 6

What is Fehling’s solution?

Answer 6

A deep blue solution used to identify aldhydes from ketones. It forms a brick red precipitate when aldehydes are present. Stays blue if ketones are present.

Question 7

What is a ketone?

Answer 7

A compound containg the C=O functinal group. These cannot be oxidised any further.

Question 8

What is a nucleophile?

Answer 8

An atom or molecule that donates an electron pair to form a covalent bond.

Question 9

Nucleophilic addition.

Answer 9

• A reaction in which an electrophilic Pi bond breaks reacts with a nucleophile breaking its Pi bond.
• This forms two new sigma bonds.

Question 10

Oxidation

Answer 10

The loss of electrons/increase in oxidatino number.

Question 11

Reduction is…

Answer 11

The gain of electrons/decrease in oxidation number.

Question 12

How are aldehydes formed?

Answer 12

The oxidation of primary alcohols with acidified potassium dichromate (H⁺/Cr₂O₇^2-)

Question 13

How are ketones formed?

Answer 13

The oxidation of secondary alcohols with acidified potassium dichromate (H⁺/Cr₂O₇^2-)

Question 14

How can we distinguish between aldehydes and ketones?

Answer 14

Tollen’s reagent produces a silver mirror if an aldehyde is present. The silver ions oxidise the aldehyde and produces the postive test.

Fehling’s solution is turns from blue to red if an aldehyde is present.

Question 15

How can aldehydes and ketones be reduced?

Answer 15

Using NaBH₄

Question 16

When can 2,4-DNP be used?

Answer 16

To identify if a solution has a ketone or an aldehyde.

Question 17

When is an iodoform reaction used?

Answer 17

To identify if a carbonyl compound that contains a methyl secondary alcohol or ethanol is present. The reagents are iodine and soidum hydroxide_(aq).

A psoitive result will give a yellow precipitate of CHI₃