Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

A-level Chemistry > CbD - Carbonyl compounds > Flashcards

CbD - Carbonyl compounds Flashcards

1
Q

How can aldehydes and ketones be made?

A

By oxidising alcohols.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Examples of carbonyl compounds

A

Aldehydes and ketones.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How do you make an aldehyde?

A

Gently heat a primary alcohol with an oxidising agent.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What oxidising agent is usually used when making an aldehyde?

A

Acidified potassium dichromate(VI).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What do aldehydes oxidise further to make?

A

Carboxylic acids.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What do you have to do make an aldehyde not oxidise further into carboxylic acids?

A

You’ve got to distil the aldehyde out of the reaction as soon as it’s formed to stop it oxidising further.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How do you make a ketone?

A

Reflux a secondary alcohol with an oxidising agent.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What can you use to test for aldehydes and ketones?

A

Fehling’s solution and Tollens reagent.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What can Fehling’s solution be used to test for?

A

Aldehydes and ketones.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is Fehling’s solution?

A

A blue solution of complexed copper(II) ions dissolved in sodium hydroxide. Fehling’s A and Fehling’s B.

(Fehling’s A = Cu2+ weak oxidising agent. Fehling’s B = alkaline solution containing a bidentate ligand.)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What does Fehling’s solution do to aldehydes?

A

Oxidises them to carboxylic acids.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Result when Fehling’s solution is mixed with an aldehyde

A

Blue solution –> Brick red precipitate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Result when Fehling’s solution is mixed with a ketone

A

Nothing happens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Explain how you’d use Fehling’s solution to test for aldehydes and ketones

A

1) Add 2cm3 of Fehling’s solution to a test tube (or Benedict’s solution). It should be a clear blue solution.
2) Add 5 drops of the aldehyde or ketone to the test tube.
3) Put the test tube in a hot water bath to warm it for a few minutes.

Aldehyde - blue solution to brick red precipitate.
Ketone - nothing happens.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Explain what is happening when you add Fehling’s solution to an aldehyde

A

Blue copper(II) ions (Cu^2+) in the Fehling’s solution are reduced (the electrons come from the oxidation of the aldehyde) forming copper(I) ions (Cu+) which then form a brick red precipitate of copper(I) oxide (Cu2O).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How do you make Tollens reagent?

A

1) Put 2cm3 of 0.1 mol dm-3 (colourless) silver nitrate solution in a test tube.
2) Add a few drops of dilute sodium hydroxide solution. A light brown precipitate should form (silver oxide).
3) Add drops of dilute ammonia solution until the brown precipitate dissolves completely. This is now Tollens reagent.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is Tollens reagent?

A

Dissolved silver(I) oxide (Ag2O) in ammonia solution to form the [Ag(NH3)2]+ (aq) complex ion.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What can Tollens reagent be used to test for?

A

Aldehydes and ketones.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How do you use Tollens reagent to test for aldehydes and ketones?

A
  • Place the test tube with Tollens reagent in a hot water bath and add 10 drops of aldehyde or ketone.
  • Wait for a few minutes.

Aldehyde - a silver mirror (a thin coating of silver) forms on the walls of the test tube.
Ketone - nothing happens.

20
Q

Explain what is happening when you add Tollens reagent to an aldehyde

A

Diamminesilver ions in the Tollens reagent (the silver(I) ions) are reduced (the electrons come from the oxidation of the aldehyde) to elemental silver, which appears as a silvery layer on the inner surface of the test tube.

21
Q

Why must the test tubes be heated in a water bath rather than using a bunsen when testing for the aldehydes and ketones?

A

Aldehydes and ketones are flammable.

22
Q

Equation of what is happening when testing for aldehydes using Fehling’s solution

A

Cu^2+ (aq) + e- –> Cu+ (s)

23
Q

What is the aldehyde oxidised into when it reacts with Fehling’s solution/Tollens reagent?

A

RCHO is oxidised to the carboxylate ion RCOO-.

24
Q

Equation of what is happening when testing for aldehydes using Tollens reagent

A

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

25
Q

Colour change when an aldehyde reacts with acidified dichromate

A

orange –> green

26
Q

Colour change when an aldehyde reacts with Fehling’s solution

A

blue –> brick-red

27
Q

Colour change when an aldehyde reacts with Tollens reagent

A

clear –> silver (silver mirror effect)

28
Q

Colour change when a ketone reacts with acidified dichromate

A

stays orange

29
Q

Colour change when a ketone reacts with Fehling’s solution

A

stays blue

30
Q

Colour change when a ketone reacts with Tollens reagent

A

no change (colourless still)

31
Q

What is the original colour of acidified dichromate?

A

orange

32
Q

What is the original colour of Fehling’s solution?

A

blue

33
Q

What is the original colour of Tollens reagent?

A

colourless

34
Q

Through what reaction will hydrogen cyanide react with carbonyls?

A

Nucleophilic addition

35
Q

What is produced when hydrogen cyanide reacts with carbonyl compounds?

A

Cyanohydrins

36
Q

What are cyanohydrins?

A

Molecules with a -CN and an -OH group.

37
Q

What is hydrogen cyanide?

A

A weak acid

38
Q

What does it mean that hydrogen cyanide is a weak acid?

A

It partially dissociates in water to form H+ ions and CN- ions.

39
Q

How does hydrogen cyanide react with carbonyls by nucleophilic addition?

A

1) The CN- group attacks the partially positive carbon atom and donates a pair of electrons. Two electrons from the double bond transfer to the oxygen.
2) H+ (from either hydrogen cyanide or water) bonds to the oxygen to form the hydroxyl group (-OH).

40
Q

Why is hydrogen cyanide bad?

A

It is a highly poisonous gas.

41
Q

How does the nucleophilic addition of hydrogen cyanide with carbonyl compounds need to be carried out?

A

In a fume cupboard - as it is a highly poisonous gas.

42
Q

What are cyanohydrins also known as?

A

Hydroxynitriles.

43
Q

What is the cyano- functional group (nitrite group)?

A

N≡C^-

44
Q

What is the cyano- group as an ion in an inorganic salt called?

A

Cyanide

45
Q

What is the cyano- group in an organic compound called?

A

A cyano- group or nitrile group

A-level Chemistry (51 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions