Carboxylic Acids & Esters

Question 0

Explain the effect of carbon chain length on the solubility of carboxylic acids

Answer 0

As the number of carbon atoms in the carboxylic acid increases, the solubility decreases

Question 1

Explain the water solubility of carboxylic acids

Answer 1

The highly polar C=O and O-H bonds allow carboxylic acid molecules to form hydrogen bonds with water molecules

Question 2

Carboxylic acid + metal –>

Answer 2

Carboxylate + H2

Question 3

Carboxylic acid + metal hydroxide –>

Answer 3

Carboxylate + H2O

Question 4

Carboxylic acid + metal carbonate –>

Answer 4

Carboxylate + CO2 + H2O

Question 5

Describe how an ester can be made from an alcohol and a carboxylic acid

Answer 5

Alcohol + carboxylic acid –> ester + water

Conditions: Heat under reflux, concentrated H2SO4 catalyst

Question 6

Describe how an ester can be made from an alcohol and an acid anhydride

Answer 6

Alcohol (or phenol) + acid anhydride –> ester + carboxylic acid
Conditions: gentle heating
This method gives a much better yield

Question 7

General structure of a carboxylate

Answer 7

RCOO-M+

Question 8

General structure of an acid anhydride

Answer 8

RCOOCOR

they are always symmetrical

Question 9

Describe acid hydrolysis of esters

Answer 9

The ester is broken down by water, to form a carboxylic acid and an alcohol
Conditions: Heat under reflux, dilute H2SO4 or HCl (acts as a catalyst)
This is a reversible reaction

Question 10

Describe alkaline hydrolysis of esters

Answer 10

A carboxylate and an alcohol is formed
Conditions: Heat under reflux, aqueous KOH or NaOH (NOT a catalyst)
This is a non-reversible reaction

Question 11

What can esters be used for?

Answer 11

They can be used as perfumes and flavourings

Question 12

Describe a triglyceride

Answer 12

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

Question 13

Describe the structure of a saturated fatty acid

Answer 13

They are long-chain carboxylic acids with no double bonds

Question 14

Fats and oils are derived from…

Answer 14

Saturated or unsaturated fatty acids

Question 15

Describe the structure of unsaturated fatty acids

Answer 15

Long-chain carboxylic acids with at least one C=C double bond

Question 16

Describe the structure of a fatty acid

Answer 16

A long-chain carboxylic acid

Question 17

Explain the relative melting points of unsaturated and saturated fats

Answer 17

Unsaturated fats have restricted rotation around the double bond so they cannot pack together as tightly, this means they have less intermolecular forces, so have lower melting points

Question 18

Explain the relative melting points of cis and trans fats

Answer 18

In the cis form, the molecules cannot pack together closely, so they have less intermolecular forces, so lower melting points

Question 19

What is the relation of trans fats to our health?

Answer 19

Trans fats, although a type of unsaturated fat, can increase cholesterol, and therefore increase the risk of coronary heart disease

Question 20

What can esters of fatty acids be used for?

Answer 20

They are used as biodiesel. It is much cheaper than using oil and fossil fuels, and much better for the environment. To make biodiesel, triglycerides in fats and oil are reacted with methanol or ethanol in the presence of a sodium catalyst. The atom economy for this process is higher because the glycerol made is sold to pharmaceutical companies. This process is called transesterification

Question 21

Suggest a suitable alcohol that could be used industrially to make biodiesel

Answer 21

CH3OH, because it is renewable