Aldehydes And Ketones

Question 1

What type of group do aldehydes and ketones contain?

Answer 1

A carbonyl group

Question 2

What is the difference between the carbonyl groups in aldehydes and ketones

Answer 2

• Carbonyl group is located in different positions
• Aldehydes: carbonyl group is at the end of the carbon chain- al
• Ketones: Carbonyl group is in the middle of the carbon chain- one

Question 3

What do aldehydes produce when oxidised?

Answer 3

Carboxylic acids

Question 4

Why can’t ketones be oxidised

Answer 4

They do not have a hydrogen attached to their carbonyl

Question 5

What happens to the other compound when an aldehyde is oxidised

Answer 5

The other compound is reduced

Question 6

Give the two oxidising agents to test for aldehydes and ketones and the product of the reaction

Answer 6

• Tollens reagent: colourless solution of silver nitrate dissolved in aqueous ammonia
• Tollens reagent is heated in a test tube with an aldehyde, Ag+ ions are reduced to Ag atoms and a silver mirror forms
• Ketones can’t be oxidised so there’s no colour change
• Fehling’s solution/benedict’s solution: blue solution of copper (II) ions dissolved in sodium hydroxide
• Heated with an aldehyde , the copper (II) ions are reduced to a brick-red precipitate of copper (I) oxide
• With ketones, no precipitate is formed

Question 7

What product is formed when aldehydes are reduced?

Answer 7

Alcohols

Question 8

What product is formed when secondary alcohols are oxidised

Answer 8

They form ketones

Question 9

What reducing agent is used to reduce aldehydes to alcohols

Answer 9

NaBH4 (sodium tetrahydridoborate (III) or sodium borohydride

Question 10

What type of reaction is the reduction of aldehydes to produce alcohols

Answer 10

• Nucleophilic addition reactions
• H- ions acts as a nucleophile and adds on to the s+ carbon atom

Question 11

Give the diagram for the reduction of aldehydes to form primary alcohols and ketones to secondary alcohols

Answer 11

Check physical flashcards for answers

Question 12

Give a detailed diagram of how aldehydes are reduced

Answer 12

Check physical flashcards for answers

Question 13

Where do the H- ions and H+ ions come from?

Answer 13

• H-: from the reducing agent
• H+: from water

Question 14

How does potassium cyanide react with carbonyls?

Answer 14

By Nucleophilic addition reactions

Question 15

What is the product of the reaction of potassium cyanide and carbonyls

Answer 15

Hydroxynitriles, molecules with a CN and an OH group

Question 16

Give the equation for how potassium cyanide dissociates in water

Answer 16

KCN -> K+ + CN-

Question 17

Describe the reaction between potassium cyanide and a carbonyl group (aldehyde). Give the overall equation for an aldehyde and ketone

Answer 17

• The CN- group attacks the partially positive carbon atom and donates a pair of electrons. Both electrons from the double bond transfer to the oxygen
• H+ ions add to the oxygen to form the hydroxyl group (OH). Acidified KCN is usually used so there’s a source of H+ ions
• Check physical flashcards for answers

Question 18

Why is potassium cyanide a dangerous chemical to work with and what are some safety measure

Answer 18

• Potassium cyanide is an irritant
• Dangerous if ingested or inhaled
• Reacts with moisture to produce hydrogen cyanide- highly toxic gas
•Wear gloves, safety goggles, lab coat, experiment in a fume cupboard

Question 19

Solution X reacts with liquid ketones to form a crystalline solid.

This reaction can be used to identify a ketone if the crystalline solid is separated, purified by recrystallisation, and the melting point is determined.

Describe how the crystalline solid separated and purified

Answer 19

• Filter/decant (pouring off the top content of a mixture/draining the bottom content)
• Dissolve in minimum volume of hot solvent
• Cool/leave (to crystallise) and filter (under reduced pressure)
• Wash with cold solvent/ water and dry with method

Question 20

Why is KCN used instead of HCN in the reaction with propanone

Answer 20

HCN is weak

Question 21

Draw the nucleophilic addition-elimination mechanism of a compound with a carbonyl group and halogen group that is being attacked by a alcohol to produce an ester and one to produce a halide

Answer 21

Check physical flashcards for answers

Question 22

• What are the oxidizing species in Tollens reagent
• What happens to these oxidizing species during the oxidation of carbonyls
• Write a half equation to represent this change
• Write an equation to show the reaction that takes place when Tollens reagent is warmed with pentanal
• Explain if Tollens reagent will produce a silver mirror when added to 3-methylbutanone

Answer 22

Check physical flashcards for answers