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AQA A-Level Chemistry > Aldehydes and Ketones > Flashcards

Aldehydes and Ketones Flashcards

1
Q

What is a primary alcohol oxidised to when distilled?

A

An aldehyde

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2
Q

What is a secondary alcohol oxidised to?

A

A ketone

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3
Q

Can an aldehyde be oxidised? If so, what to?

A

Yes. It can be oxidised to a carboxylic acid

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4
Q

Can a ketone be oxidised? If so, what to?

A

No, it cannot be oxidised further.

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5
Q

Acidified potassium dichromate is added to a substance. The colour changes from orange to green. What type of substance is it?

A

An aldehyde

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6
Q

There are three tests to distinguish between an aldehyde and a ketone. What are the reagents, what are their conditions, and what are the changes you’d see?

A

Acidified potassium dichromate + heat under reflux - Aldehyde orange to green, Ketone no reaction
Tollen’s reagent + gently heat - Aldehyde colourless to silver ppt, Ketone does not react
Fehling’s reagent. + gently heat - Aldehyde blue to red ppt, Ketone does not react

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7
Q

Give a balanced equation for the reduction of ethanal

A

CH3COH + 2[H] –> CH3CH2OH

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8
Q

Carbonyls can be reduced using NaBH4 in aqueous ethanol. They can also be reduced using another method. State the name of this other method, the reagents used, and the conditions.

A

Catalytic Hydrogenation.
Reagents: hydrogen, dilute H2SO4
Conditions: nickel catalyst, high pressure + temperature

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9
Q

Hydroxynitriles can be formed from aldehydes and ketones. Give the mechanism, the reagents and the conditions.

A

Mechanism: Nucleophilic addition
Reagent: sodium cyanide (NaCN) and dilute H2SO4
Conditions: room temperature and pressure

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10
Q

CH3COCH3 is reacted with NaCN and another reagent under room temp. and pressure. Name the other reagent and the product formed.

A

Dilute H2SO4
2-hydroxy-2-methylpropanenitrile

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11
Q

Nucleophilic addition of HCN to aldehydes and ketones results in the formation of a racemate. Why?

A

The middle step of the reaction is a trigonal planar carbonyl (2D). The H+ can attack from either above or below, resulting in two different enantiomers. Because the carbonyl has equal chance of being attacked

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12
Q

Give two methods of reduction

A

NaBH4 in aq ethanol
Catalytic hydrogenation

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13
Q

What is a suitable oxidising agent?

A

Acidified potassium dichromate

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14
Q

The reduction of an aldehyde or ketone involves what type of reaction mechanism?

A

Nucleophilic addition

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15
Q

Why will the nucleophilic addition reaction of carbonyl compounds (eg propanal) produce a racemic mixture?

A

It is a trigonal planar, meaning the attacking species is equally likely to attack from the top or the bottom

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16
Q

Name a mechanism for the reaction of an aldehyde with HCN

A

Nucleophilic addition

17
Q

Some were asked to distinguish between a ketone and an aldehyde. One suggested looking at the optical activity. Why would this not work?

A

The ketone is not optically active
An aldehyde can be optically active, but is formed in a racemic mixture, and so any effects will be cancelled out

18
Q

Someone wants to use acidified potassium dichromate to distinguish between an aldehyde and a ketone. What are the conditions?

A

Heat under reflux

19
Q

What test produces a silver mirror effect when an aldehyde is present?

A

Tollen’s reagent

20
Q

Someone wants to use Tollen’s reagent to distinguish between an aldehyde and a ketone. What else would they have to do to the substance? (conditions)

A

Heat gently

21
Q

What colour change is observed when Tollen’s reagent is added to an aldehyde?

A

Colourless to silver precipitate

22
Q

What colour change is observed when Tollen’s reagent is added to a ketone?

A

No visible change

23
Q

Someone wants to use Fehling’s solution to distinguish between an aldehyde and a ketone. What else would they have to do to the substance? (conditions)

A

Gently heat

24
Q

What colour change is observed when Fehling’s solution is added to an aldehyde?

A

Blue to red

25
Q

What colour change is observed when Fehling’s solution is added to a ketone?

A

No visible change

26
Q

What colour change is observed when acidified potassium dichromate is added to an aldehyde?

A

Orange to green

27
Q

What colour change is observed when acidified potassium dichromate is added to a ketone?

A

No visible change

28
Q

What are the reagents for the formation of hydroxynitriles from aldehydes/ketones?

A

Sodium cyanide (NaCN) and dilute H2SO4

29
Q

What is the reaction mechanism for the formation of hydroxynitriles from aldehydes/ketones?

A

Nucleophilic addition

30
Q

What are the conditions for the formation of hydroxynitriles from aldehydes/ketones?

A

Room temp. and pressure

31
Q

Give the reagents and conditions for the catalytic hydrogenation of an aldehyde

A

Hydrogen
Nickel catalyst
high temp

32
Q

Give the conditions for the catalytic hydrogenation of an aldehyde

A

Nickel catalyst
150*C
High pressure

AQA A-Level Chemistry (36 decks)

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