ALDEHYDES AND KETONES

Question 1

What functional group do both aldehydes and ketones have

Answer 1

Carbonyl, C=O

Question 2

What is the difference between an aldehyde and a ketone

Answer 2

The positioning of the carbonyl group

Question 3

Where is the carbonyl group on an aldehyde

Answer 3

At an end carbon

Question 4

Where is the carbonyl group on a ketone

Answer 4

On an inner carbon

Question 5

What do aldehydes end in

Answer 5

-al

Question 6

What do ketones end in

Answer 6

-one

Question 7

How are aldehydes oxidized

Answer 7

Readily

Question 8

How are ketones oxidized

Answer 8

They cannot be oxidized

Question 9

Show the oxidation of both an aldehyde and a ketone

Answer 9

…

Question 10

What test can distinguish between aldehydes and ketones

Answer 10

Tollen’s silver mirror test

Question 11

How is Tollen’s reagent made

Answer 11

Silver nitrate is added to a test tube. A few drops of sodium hydroxide is added, forming a pale brown precipitate. Add a few drops of dilute ammonia until the precipitate dissolves.

Question 12

How do you use Tollen’s to test for aldehydes

Answer 12

Add sample to a test tube of Tollen’s reagent, then place in a hot water bath. Observe the formation of a silver mirror on the test tube to confirm the presence of an aldehyde

Question 13

What is the formula of Tollen’s reagent

Answer 13

[Ag(NH3)2]+

Question 14

Why do we not use a Bunsen flame when doing the silver mirror test

Answer 14

Aldehydes and ketones are flammable

Question 15

What is Tollen’s reagent

Answer 15

An oxidizing agent

Question 16

What other than Tollen’s can be used to test for aldehydes

Answer 16

Fehling’s solution

Question 17

What color is fehlings solution and why

Answer 17

Blue as it contains cu2+ ions

Question 18

How do you test for aldehydes using fehlings solution

Answer 18

Warm it up in the presence of a sample. If aldehydes are present, the solution will go from blue to forming brick red precipitate. If ketones are present, there will be no reaction.

Question 19

What does fehlings solution consist of

Answer 19

Cu2+ ions dissolved in sodium hydroxide

Question 20

What reducing agents can be used to reduce aldehydes and ketones

Answer 20

Sodium borohydride (NaBH4) or sodium tetrahydridoborate(iii) dissolved in methanol and water

Question 21

What are aldehydes reduced to, and show the reduction formula

Answer 21

Primary alcohols

Question 22

What are ketones reduced to, and show the reduction formula

Answer 22

Secondary alcohols

Question 23

What does a reducing agent produce to reduce aldehydes and ketones to alcohols

Answer 23

Hydride ions

Question 24

Show the mechanism for the reduction of an aldehyde and ketone into an alcohol

Question 25

What type of mechanism is the reduction of an aldehyde or ketone

Answer 25

Nucleophilic addition

Question 26

Where does the H+ ion come from in the reduction of an aldehyde or ketone to an alcohol

Answer 26

The water or acid that was added to the reducing agent at the start

Question 27

What is formed when potassium cyanide reacts with carbonyl compounds such as aldehydes or ketones, and what type of reaction is this

Answer 27

Hydroxynitriles are produced, nucleophilic addition

Question 28

How is potassium cyanide used to produce CN- ions

Answer 28

When dissolved in acidic solution, it dissociates to form K+ and CN- ions. KCN -> K+ + CN-

Question 29

What can be used as a substitute for potassium cyanide when trying to produce a hyrdoxynitrile from aldehydes or ketones, and how is the preparation of this reaction different

Answer 29

Hydrogen cyanide, no acid is required

Question 30

Show the mechanism for the reaction of an aldehyde with potassium cyanide

Question 31

What is produced if we used unsymmetrical ketones or aldehydes in the reaction with potassium cyanide

Answer 31

A mixture of enantiomers is produced

Question 32

How is hydrogen cyanide produced

Answer 32

When potassium cyanide combines with moisture

Question 33

Why is potassium cyanide dangerous

Answer 33

It is an irritant and very dangerous if ingested or inhaled

Question 34

What precautions must be taken when using potassium cyanide

Answer 34

Wear gloves whilst handling Use a fume cupboard Wear a lab coat

Question 35

What is the overall generic equation for the reaction of an aldehyde with potassium cyanide

Answer 35

RCHO (aq) + KCN (aq) + H+ (aq) -> RCH(OH)CN(aq) + K+ (aq)

Question 36

What is the overall generic equation for the reaction of a ketone with potassium cyanide

Answer 36

RCOR(aq) + KCN(aq) + H+ (aq) -> RCR(OH)CN(aq) + K+(aq)

Question 37

What are aldehydes oxidized into

Answer 37

Carboxylic acids

Question 38

Why can enantiomers be formed by nucelophilic addition

Answer 38

The carbonyl group is planar, so the nucleophile can attack from above or below the plane of this carbonyl group leading to 2 isomers