Topic 17 - Carbonyl Compounds

Question 1

What can alcohols be oxidised to?

Answer 1

Aldehydes, ketones, and carboxylic acids.

Question 2

What oxidising agent is used to oxidise alcohols? Name and formula.

Answer 2

Acidified Potassium dichromate.
K2Cr2O7

Question 3

What color change is observed when potassium dichromate is reduced?

Answer 3

Orange to green.

Question 4

What can primary alcohols be oxidised to?

Answer 4

Aldehydes then carboxylic acids.

Question 5

What can secondary alcohols be oxidised to?

Answer 5

Ketones.

Question 6

What can tertiary alcohols be oxidised to?

Answer 6

Nothing using K2Cr2O7. Can be oxidised to CO2 and H2O when burnt.

Question 7

What two methods are used in the oxidation of alcohols?

Answer 7

Distillation and reflux.

Question 8

What method is used to remove the aldehyde from the oxidising agent when oxidising primary alcohols?

Answer 8

Distillation.

Question 9

What method is used to create a carboxylic acid when oxidising primary alcohols?

Answer 9

Reflux and excess oxidising agent.

Question 10

What is the benefit of reflux when oxidising primary alcohols?

Answer 10

Allows strong heating without losing volatile reactants and products. Aldehydes evaporate, condense, and fall back into the flask.

Question 11

What method is used to make a ketone from a secondary alcohol?

Answer 11

Reflux and an oxidising agent.

Question 12

What is Tollen’s reagent used for?

Answer 12

Distinguishing between aldehydes and ketones.

Question 13

What are the 3 steps to make Tollen’s reagent?

Answer 13

1. Use Silver nitrate solution (colorless).
2. Add a few drops of NaOH (pale brown precipitate forms).
3. Add a few drops of dilute ammonia until precipitate dissolves.

Question 14

Why should you never use a bunsen burner when testing aldehydes and ketones with Tollen’s reagent?

Answer 14

Aldehydes and ketones are flammable.

Question 15

What is the formula for Tollen’s reagent?

Answer 15

[Ag(NH3)2]+

Question 16

What happens when warm Tollen’s reagent is added to an aldehyde?

Answer 16

Silver ‘mirror’ formed which coats the inside of the flask. Tollen’s is reduced.

Question 17

What happens when warm Tollen’s reagent is added to a ketone?

Answer 17

No silver precipitate formed.

Question 18

What are the two solutions used to distinguish between aldehydes and ketones?

Answer 18

Tollen’s reagent and Fehling’s reagent.

Question 19

What sort of agent is Fehling’s solution?

Answer 19

An oxidising agent.

Question 20

What color is Fehling’s solution and why?

Answer 20

Blue because it contains Cu2+ ions.

Question 21

What color change occurs when Fehling’s solution is added warm to an aldehyde?

Answer 21

Blue solution to brick red precipitate.

Question 22

What color change occurs when Fehling’s solution is added warm to a ketone?

Answer 22

No color change.