Carboxylic Acids and Esters

Question 1

Explain the water solubility of carboxylic acids

Answer 1

• soluble in water as highly polar C=O and O-H bonds form hydrogen bonds with water.
• as the length of chain increases, solubility decreases as the non polar part of the chain does not interact with water.

Question 2

Describe the reactions of carboxylic acids

Answer 2

1) metal + carboxylic acid -> salt + hydrogen gas
2) Base + carboxylic acid -> salt + water
3) carbonates + carboxylic acid -> salt + water + CO2

Question 3

When naming esters, what part of the name comes from the alcohol and what part comes from the acid?

Answer 3

First part: alcohol (ending -yl)

Second part: acid (ending -oate)

Question 4

Describe the esterification of carboxylic acids with alcohols

Answer 4

Conc sulphuric acid is used as the catalyst.
CH3CH2COOH + CH3CH2OH -> CH3CH2COOCH2CH3 + H2O
propanoic acid + ethanol -> ethyl propanoate + water

Question 5

How are acid anhydrides formed?

Answer 5

Two carboxylic acid molecules
H removed from one carboxylic acid
OH from the other carboxylic acid
(Makes H2O and anhydride)

Question 6

What is the benefit of using anhydrides?

Answer 6

They give a better yield of the ester

Question 7

Describe how esters can be formed from acid anhydrides

Answer 7

Heating an acid anhydride with an alcohol
anhydride + alcohol -> ester + carboxylic acid
eg: Ethanoic anhydride + methanol -> methyl ethanoate + Ethanoic acid

Question 8

Describe the hydrolysis of esters with hot aqueous dilute acid

Answer 8

-the ester is broken down by water, with the acid acting as a catalyst

Question 9

Describe the hydrolysis of esters with hot aqueous alkali (eg sodium or potatassium)

Answer 9

Non reversible, leads to sodium salt of carboxylic acid and another organic product.

Question 10

State the uses of esters

Answer 10

Perfumes

Flavourings

Question 11

What is a triglyceride?

Answer 11

A triglyceride is a triester of glycerol (propane-1,2,3-triol) and fatty acids

Question 12

Compare the structures of saturated fats, unsaturated fats and fatty acids

Answer 12

Saturated - no double bonds between carbons
Unsaturated - has double bonds between carbons
Triglycerides - 3 fatty acids joined to each of the alcohol groups on glycerol through ester linkages

Question 12

Compare the link between Trans fatty acids, the possible increase in “bad” cholesterol and CHD

Answer 12

Trans fats are said to be damaging for health because they raise LDL levels (bad cholesterol). There are more points of contact so more intermolecular forces

Question 13

Describe and explain the increased use of esters as biodiesel.

Answer 13

Triglycerides are used to form biodiesel. A triglyceride is reacted with methanol with an alkaline catalysts (eg NaOH). The methanol replaced the glycerol, forming biodiesel