3.3.8 Aldehydes and Ketones

Question 1

Name 2 carbonyl compounds

Answer 1

Aldehydes and ketones

(both contain carbonyl functional group C=O)

Question 2

Draw an aldehyde

Answer 2

Question 3

Draw a ketone

Answer 3

Question 4

State which compound reacts with oxidising agents: aldehydes or ketones. Include the product formed.

Answer 4

React with aldehydes to produce carboxylic acids

Question 5

Name 2 reagents you can use to test for aldehydes

Answer 5

• Tollens’ reagent
• Fehling’s solution

Question 6

What is Tollens’ reagent?

Answer 6

Colourless solution of silver nitrate dissolved in aqueous ammonia

Question 7

Describe what happens when Tollens’ reagent is heated in a test tube with an aldehyde

Answer 7

• Ag⁺ ions in Tollens’ reagent are reduced to Ag atoms
• Silver mirror forms

Question 8

What is Fehling’s solution?

Answer 8

Blue solution of copper(II) ions dissolved in sodium hydroxide

Question 9

Describe what happens to Fehling’s solution when it’s heated with an aldehyde

Answer 9

Copper(II) ions are reduced to brick-red precipitate of copper(I) oxide

Question 10

When primary alcohols are oxidised, what products are produced?

Answer 10

Aldehydes and carboxylic acids

(Can use reducing agent to reverse these reactions)

Question 11

When secondary alcohols are oxidised, what product is produced?

Answer 11

Ketones

(Can use reducing agent to reverse these reactions)

Question 12

State a reducing agent you can use to reduce aldehydes and ketones

Answer 12

NaBH₄ dissolved in water with methanol

Question 13

In equations, what does the [H] stand for?

Answer 13

Hydrogen from reducing agent

Question 14

Write an equation showing the reduction of an aldehyde to a primary alcohol. Draw molecules in displayed formula.

Answer 14

Question 15

Write an equation showing the reduction of a ketone to a secondary alcohol. Draw molecules in displayed formula.

Answer 15

Question 16

Draw the reaction mechanism for the reduction of an aldehyde to a primary alcohol. Include the name of the reaction mechanism.

Answer 16

Nucleophilic addition

H^- ion acts a nucleophile and adds on δ⁺ on carbon atom

Question 17

When potassium cyanide reacts with carbonyl compounds, what products are produced?

Answer 17

Hydroxynitriles (molecules with CN and OH)

Question 18

What type of reaction mechanism occurs when potassium cyanide reacts with carbonyl compounds?

Answer 18

Nucleophilic addition reaction

Question 19

When potassium cyanide reacts with carbonyl compounds, why it is considered a nucleophilic addition reaction?

Answer 19

∵ nucleophile attacks the molecule & add itself as an extra group

Question 20

Write an equation for when potassium cyanide dissociates in water

Answer 20

KCN → K⁺ + CN^-

Question 21

Draw the reaction mechanism for when potassium cyanide reacts with a ketone

Answer 21

Question 22

Write the overall equation for when potassium cyanide reacts with aldehydes

Answer 22

Question 23

Write the overall equation for when potassium cyanide reacts with ketones

Answer 23

Question 24

When you react potassium cyanide with an unsymmetrical ketone or any aldehyde (expect methanal), what will you produce?

Answer 24

Mixture of enantiomers

Question 25

Describe how potassium cyanide is hazardous

Answer 25

• Potassium cyanide = irritant & extremely dangerous if ingested or inhaled
• Can react with moisture to produce hydrogen cyanide = highly toxic gas

Question 26

State what you can do to reduce the risks of potassium cyanide

Answer 26

Wear gloves, safety goggles and lab coat & perform experiment in fun cupboard

Question 27

Write the overall equation for the addition of hydrogen cyanide to an aldehyde

Answer 27

RCHO + HCN → RCH(OH)CN