Esters

Question 1

How are esters formed?

Answer 1

Esters are formed by the condensation reaction between a carboxylic acid and an alcohol.

Question 2

When producing an ester what is the function of the ‘wet paper towel’ condesner?

Answer 2

To prevent reactants and products escaping from the reaction vessel in vapour form.

Question 3

When producing an ester why was concentrated sulfuric acid used?

Answer 3

It acts as a catalyst.

Question 4

Why is a water bath used instead of a Bunsen burner when producing a ester?

Answer 4

Some of the reactants and products are flammable.

Question 5

What is the purpose of the sodium hydrogen carbonate solution?

Answer 5

To neutralise the concentrated sulfuric acid and any unreacted carboxylic acid.

Question 6

Give two suggestions seen when a ester has been formed?

Answer 6

There is an oily layer on the surface and there is a distinctive smell.

Question 7

What is the ester link shown as in molecular formulae?

Answer 7

-COO-

Question 8

What is hydrolysis?

Answer 8

To split a compound by adding water.

Question 9

What can hydrolysis be used for in esters?

Answer 9

The parent carboxylic acid and alcohol can be obtained.

Question 10

What is distillation?

Answer 10

Distillation is a process to separate the alcohol from the reaction mixture.

Question 11

What are fats and oils?

Answer 11

Fats and oils are triglycerides and edible fats and oils are esters.

Question 12

What functional group do they contain?

Answer 12

An ester link.

Question 13

What does the hydrolysis of fats and oils produce?

Answer 13

Fatty acids and glycerol in the ratio of three fatty acids to one glycerol.

Question 14

What is glycerol known as?

Answer 14

Trihydric alcohol and propan-1,2,3-triol.

Question 15

How are fatty acids and oils formed?

Answer 15

By the condensation of glycerol and three carboxylic acid molecules.

Question 16

What is the structural difference between unsaturated and saturated fatty acids?

Answer 16

Unsaturated contains a double carbon to carbon bond and there is a kink in the chain.

Question 17

How can you tell if a fatty acid is unsaturated, monounsaturated or poly unsaturated?

Answer 17

Substitute an H for the COOH group. Recognise which it is
Alkane CnH2n+2 - Saturated
Alkene CnH2n - Poly or mono unsaturated
Note: If it is poly, it will not fit the alkene or alkane formulas and will have less hydrogens.

Question 18

What is the difference between fats and oils?

Answer 18

Fats are solid at room temperature and oils are liquids at room temperature.

Question 19

What is the lower melting point of oil related to?

Answer 19

The degree of unsaturation in the oil molecule.

Question 20

describe why oils have a lower melting point than fats.

Answer 20

The greater the degree of unsaturation, the lower the melting point.

Question 21

Explain fully why oils have a lower melting point than fats.

Answer 21

Double bonds in the fatty acid chains prevent oil molecules from packing closely together, so the greater the number of double bonds present, the weaker the London dispersion forces of attraction.
Note: fats don’t or do always have double bonds.

Question 22

What test could be done to determine the degree of unsaturation?

Answer 22

Unsaturated compounds quickly decolourise bromine solution.

Question 23

How can vegetable oils form margarine?

Answer 23

Can be hydrogenated using a nickel catalyst.

Question 24

What is hydrogenation?

Answer 24

The addition of hydrogen across a carbon do carbon bond.

Question 25

What is halogenation?

Answer 25

The addition of a halogen across a carbon to carbon double bond.

Question 26

What is hydration?

Answer 26

Hydration is the addition of water across a carbon to carbon double bond to form an alcohol.

Question 27

What is condensation?

Answer 27

Condensation is a reaction when two molecules are joined together with the loss of a small molecule such as water.

Question 28

What is hydrolysis?

Answer 28

Hydrolysis is a reaction when a molecule reacts with water to break down into smaller molecules.

Question 29

Describe how soap works?

Answer 29

Soap contains a hydrophobic part and hydrophilic part. Hydrophilic is ionic and hydrophobic is non polar. The hydrophobic part dissolves in water and the hydrophilic part dissolves in oil. Agitation separates oil from the surface and causes small oil droplets to form. The negatively charged ball structures repel each other in water and the oil is suspended in the water.

Question 30

How are emulsifiers formed?

Answer 30

By reacting edible oils with glycerol.

Question 31

What do emulsions do?

Answer 31

Allows a small droplet of a liquid to remain suspended in another and prevents the liquids from separating into two layers.

Question 32

What are examples of emusions?

Answer 32

Grease particles mixed in soap, milk, mayonnaise and ice cream.

Question 33

What do emulsifiers contain?

Answer 33

One part of the molecules is hydrophobic and the other is hydrophilic. The OH group dissolves in water and the fatty acid dissolves in the oil.

Question 34

What happens when food ‘goes off’

Answer 34

It oxidises.

Question 35

What happens when fats and oils are in contact with air at room temperature?

Answer 35

They undergo oxidation and hydrolysis turning them rancid and acquiring a disagreeable odour.

Question 36

What causes the disagreeable odour in the oxidation of food?

Answer 36

The release of volatile fatty acids by hydrolysis of the ester bond.

Question 37

What is condensation polymers?

Answer 37

are made from monomers with two functional groups per molecule.