Chapter 26: Compounds Containing The Carbonyl Group Flashcards Preview

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Flashcards in Chapter 26: Compounds Containing The Carbonyl Group Deck (26)
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1
Q

Properties of carbonyl compounds

A

C=O is strongly polar.
So there are permanent dipole dipole forces between the molecules.
This means they have higher melting points than those of alkenes of comparable relative molecular mass. But not as high as those of alcohols, where hydrogen bonding can occur.

2
Q

Solubility of short chain ketones and aldehydes.

A

Shorter chain aldehydes and ketones mix completely with water.
As hydrogen bonds form between oxygen of carbonyl compound and water.

3
Q

What happens to the solubility of ketones and aldehydes as the length of carbon chain increases?

A

Solubility decreases.

4
Q

Reactions of carbonyl compounds.

A

Nucleophilic addition reactions.

5
Q

Oxidising agent used to oxidise aldehydes to carboxylic acids.

A

Acidified (with dilute sulphuric acid) potassium dichromate (VI), K2Cr2O7/H+

6
Q

Why can’t ketones be easily oxidised easily to carboxylic acids?

A

A C-C bond must be broken. Stronger oxidising agents must be used to get a shorter chain molecule, carbon dioxide and water.

7
Q

What is fehlings solution?

A

Fehling’s A: Cu2+ ions and coloured blue.

Fehling’s B: an alkali and a complexing agent.

8
Q

What happens when an aldehydes is warmed with Fehling’s solution?

A

Brick red precipitate of copper (I) oxide is produced as the copper (II) oxidises the aldehyde to a carboxylic acid, and itself is reduced to copper (I).

9
Q

What happens when a ketone is warmed with fehling’s solution?

A

Nothing.

10
Q

What happens when a ketone is warmed with tollen’s reagent?

A

Nothing.

11
Q

What happens when an aldehydes is warmed with tollen’s reagent?

A

Metallic silver is formed.
Aldehydes are oxidised to carboxylic acids by tollen’s reagent. The Ag+ is reduced to metallic silver. A silver mirror is will be formed on the inside of the test tube.

12
Q

What is tollen’s reagent?

A

Contains the complex ion [Ag(NH3)2]+ which is formed when aqueous ammonia is added to an aqueous solution of silver nitrate.

13
Q

Mechanism for reducing aldehydes and ketones?

A

Nucleophilic addition reactions.

14
Q

True or false.

Carboxylic acids up to and including four carbons are completely soluble in water. And why?

A

True.

As the carboxylic acid group can form hydrogen bonds with water molecules.

15
Q

True or false.

Carboxylic acids have a lower melting point than the alkanes of similar relative molecular mass. And why?

A

False, carboxylic acids have higher melting points than that of alkanes of similar relative molecular mass. This is due to carboxylic acids forming hydrogen bonds with one another in the solid state.

16
Q

How can you identify carboxylic acids?

A

Measure the melting point and compare it with table of known melting points.
A thiele tube may be used or the melting point can be found electrically.

17
Q

Acids have characteristic…

A

Smells.
E.g.
Ethanoic acid= vinegar
Butanoic acid= rancid butter

18
Q

Uses of esters.

A

Flavourings
Perfumes
Solvents
Plasticisers

19
Q

Esters have…

A

Fruity smells and are volatile.

20
Q

Carboxylate ion

A

When a hydrogen is removed from a carboxylic acid.

21
Q

What makes the carboxylate ion more stable?

A

Delocalisation.

22
Q

As carboxylic acids are weak acids, the equilibrium is over to the…

A

Left.

23
Q

How is an ester hydrolysed?

A

A strong acid catalyst is used at room temperature.

24
Q

What happens if a base is used to hydrolysed an ester?

A

Salt of the acid is produced rather than the acid itself.

In this, an equilibrium is not established and the reaction goes to completion, so there is more product in the mixture.

25
Q

Hydrolysis of an ester

A

Does not go to completion, it produces an equilibrium mixture containing the ester, water, acid and alcohol.

26
Q

Uses of glycerol

A
  • Used as a solvent in medicines.
  • Used as a solvent in the food industry.
  • Used to plasticise materials such as sheets and gaskets.
  • Used in cosmetic and pharmaceutical preparations.