Aldehydes and ketones

Question 1

What type of chemical group can be found in aldehydes?

Answer 1

Aldehydes have a carbonyl group, C=O, at the end of a carbon chain.

Question 2

What do aldehydes oxidise to form?

Answer 2

We can oxidise aldehydes to form carboxylic acids?

Question 3

How can we achieve oxidation of aldehydes?

Answer 3

To achieve this we heat aldehydes with potassium dichromate and sulfuric acid under reflux

Question 4

What is the oxidising agent in the oxidation of aldehydes?

Answer 4

The potassium dichromate is the oxidising agent

Question 5

What is the colour change when oxidising aldehydes to carboxylic acids?

Answer 5

Orange to Green

Question 6

What is responsible for the colour change?

Answer 6

The change in the oxidation state of the chromium gives the colour change.

Question 7

Give the reaction equation for enthanal

Answer 7

3CH₃CHO + Cr₂O₇²⁻ + 8H⁺&raquo_space;> 3CH₃COOH + 2Cr³⁺ + 4H₂O

Question 8

What can the reaction equation for enthanal be simplified to?

Answer 8

CH₃CHO + [O]&raquo_space;> 3CH₃COOH

Question 9

Can Aldehydes and Ketones form hydrogen bonds?

Answer 9

It is not possible for aldehydes or ketones to form intermolecular hydrogen bonds as all the hydrogen is joined to carbon

Question 10

What type of attractions are present in aldehydes and ketones?

Answer 10

There is permanent dipole-dipole attractions due to the polar C=O bonds.

Question 11

Estimate the strength of the intermolecular forces

Answer 11

The strength of the intermolecular forces is between that of alcohols, which can hydrogen bond and alkanes which only have London forces. This means that for the same length carbon chain, the boiling temperature of a n aldehyde or ketone is between that of the alcohol and alkane