3.3.8 - Aldehydes And Ketones

Question 1

Aldehydes end in …
And give example

Answer 1

• Anal
  Eg pentanal

Question 2

Ketones end in …
Give example ..

Answer 2

-one
Eg propanone

Question 3

What is carbonyl group

Answer 3

C=O

Question 4

Can ketones be oxidesued

Answer 4

No

Question 5

Aldehydes can be readily oxidised to ..

Answer 5

Carboxylic acids

Question 6

Propanal oxidised to…

Answer 6

Propanoic acid

Question 7

How to distinguish between aldehyde and ketone
(2 ways)

Answer 7

Tollens reagent
Fehlings solution

Question 8

+ve result for aldehyde using tollens

Answer 8

Silver mirror

Question 9

-ve test result for ketone using tollens

Answer 9

No visible change

Question 10

What colour is fehlings solution and whag is it

Answer 10

Blue solution of copper (ll) ions
Dissolves in NaOH

Question 11

+ve test result for aldehydes using fehlings solution

Answer 11

Brick red ppt
Of copper (l) oxide

Question 12

A primary alchol can be oxidised into a …. And then to a …

Answer 12

1• alcohol —-> aldehyde —> carboxylic acid

Question 13

Secondary alcohol can be oxidised into a …

Answer 13

Ketone

Question 14

Aldehydes can be reduced into ..

Answer 14

Primary alchol

Question 15

Ketones can be reduced into …

Answer 15

Secondary Alcohol

Question 16

What is the reducing agent

Answer 16

NaBH4

Question 17

CN can react with carbonyls to undergo nucleophillic addition via

Answer 17

Reacting w KCN
or HCN

Question 18

How to draw cyanide ion

Answer 18

• :CN

Lone pair … minus sign must be on top of carbon

Question 19

Aldehydes and unsymmetric ketones form mixtures of _____ When reacted with KCN followed by a dilute acid

Answer 19

Enantiomers

Question 20

Hazards of using KCN

Answer 20

• is an irritant, dangerous if digested or inhaled
• toxic and poisonous

Question 21

why is KCN used instead of HCN

Answer 21

HCN is weak

Question 22

General equation for reacting aldehyde with KCN

Answer 22

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

Question 23

Equation for overall reaction between ketone and KCN

Answer 23

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

Question 24

why does NaBH4 reduced butanal but not butene

Answer 24

3 H–
ion / nucleophile is attracted to δ+ C
1
M4 electron rich C=C
1
M5 H–
ion / nucleophile is repelled by C=C
OR
C=C only attacked by/reacts with electrophiles

Question 25

Why is a mixture of enantiomers formed when reacting an unsymmetrical ketone or any aldehyde (except methanal) with KCN

Answer 25

Double bonds in carbonyl groups ( C=O)
These C=O are planar so equal change that nucleophile will attach from either directions (top or bottom)
Thus an equal amount of each enantiomer will be formed
—> racemic mixture of products

Question 26

Overall equations for reduction reactions for aldehydes and ketones using [H]

Answer 26

Aldehyde or ketone + [H] —> alcohol

Question 27

Equation for reduction of ethanal using [H]

Answer 27

CH3CHO + 2[H] —> CH3CH2OH

Question 28

This question is about ketones.
(a) 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 determined.
Describe how the crystalline solid is separated and purified.

Answer 28

filter
dissolve in minimum volume of hot solvent

cool / leave (to crystallise) AND filter (under reduced pressure)

Wash with cold solvent/water, and dry w filter paper

Question 29

describe what happens when a reaction mixture is refluxed and why it is necessary, in this case, for complete oxidation to ethanoic acid

Answer 29

A mixture of liquids is heated to boiling point for a prolonged time

Vapour is formed which escapes from the liquid mixture, is changed
back into liquid and returned to the liquid mixture

Any ethanal and ethanol that initially evaporates can then be oxidised