Carbonyl compounds

Question 1

Structural formula of propanone

Answer 1

CH3COCH3

Question 2

structural formula of propanal

Answer 2

CH3CH2CHO

Question 3

aldehyde + ketone functional group

Answer 3

C=O (carbonyl)

Question 4

what type of boiling point to aldehydes and ketones have

Answer 4

lower boiling point than equivalent alcohols

Question 5

explain why aldehydes and ketones have a low boiling point

Answer 5

• don’t have polar OH bond so can’t form hydrogen bonds with other aldehyde/ketone molecules
• lower boiling point than equivalent alcohols which do form hydrogen bonds (strongest intermolecular force)

Question 6

name the forces within aldehydes and ketones

Answer 6

• london forces
• permanent dipole- permanent dipole

Question 7

describe solubility of aldehydes and ketones

Answer 7

• soluble in water
• lone pair of electrons on O of C=O
• form hydrogen bonds with H atoms on water molecules

Question 8

when are aldehydes and ketones not soluble

Answer 8

• longer chained ketones + aldehydes cannot H bond with water
• hydrocarbon chains disrupt H bonding between water molecules
• london forces between aldehyde + ketone molecules (+) hydrogen bonding between water molecules stronger than hydrogen bonding between water + aldehyde/ketone
• compound won’t dissolve

Question 9

which compound can be oxidised further

Answer 9

aldehydes

Question 10

describe test for aldehyde with Fehlings/benedicts solution

Answer 10

• Fehlings: Copper(II) ions dissolved in sodium hydroxide
  -Benedicts: Copper(II) ions dissolved in sodium carbonate
  -positive result- Blue- Brick red precipitate

Question 11

Fehlings/Benedicts reduction equation

Answer 11

Cu2+ (aq) + e- –> Cu+ (s)

Question 12

Describe tollens reagent

Answer 12

colourless solution of silver nitrate dissolved in aqueous ammonia

Question 13

describe test with Tollens reagent

Answer 13

• heated in a test tube (water bath) with sample
• ‘silver mirror’ forms

Question 14

tollens reagent reduction equation

Answer 14

Ag(NH3)2(aq)+ + e- –> Ag(s) + 2NH3(aq)

Question 15

what is acidified potassium dichromate

Answer 15

oxidising agent

Question 16

describe test with acidified (VI) potassium dichromate

Answer 16

• heat sample with acidified potassium dichromate
• aldehyde oxidised- colour change orange to green

Question 17

reduction equation of dichromate ions

Answer 17

Cr2O72- + 14H+ + 6e- –> 2Cr3+ + 7H2O

Question 18

what is an oxidising agent represented with

Answer 18

[O]

Question 19

oxidation equation of ethanol

Answer 19

CH3CH2OH + [O] –> CH3CHO + H2O

Question 20

name a reducing agent

Answer 20

Lithium aluminium tetrahydride (LiAlH4)

Question 21

what is a reducing agent represented with

Answer 21

[H]

Question 22

conditions for reduction of carbonyls

Answer 22

LiAlH4 in dry ether

Question 23

reduction equation of ethanal

Answer 23

CH3CHO + 2[H] –> CH3CH2OH

Question 23

reduction equation of propanone

Answer 23

CH3COCH3 + 2[H] –> CH3CH(OH)CH3

Question 24

Give the name for Brady’s reagent

Answer 24

2-4 DNPH

Question 25

what tests for a carbonyl group and what is the positive result

Answer 25

• 2-4 DNPH
• orange precipitate

Question 26

what is a methyl carbonyl and what is used to test for it

Answer 26

• methyl group attached to C=O
• iodine with heat and alkaline conditions

Question 27

positive result with test for methyl carbonyl

Answer 27

yellow precipitate (CH3I) + antiseptic smell

Question 28

conditions for formation of hydroxynitrile

Answer 28

• HCN in presence of KCN

Question 29

what type of reaction forms hydroxynitriles

Answer 29

nucleophilic addition

Question 30

mechanism for reaction of carbonyl group + CN

Question 31

considerations with reaction with HCN

Answer 31

HCN highly toxic gas.
- reaction should be done in a lab, using solution of acidified potassium cyanide
- reaction in fume cupboard, wearing lab coat, gloves and safety glasses