Unit 2 - Nature's Chemistry (Esters, Fats, and Oils)

Question 1

What are esters?

Answer 1

A small molecule that contains an ester link (-COO). They are non-polar, have characteristic smells, and insoluble in water.

Question 2

How are esters formed?

Answer 2

Formed by the condensation reaction between an alcohol and a carboxylic acid. This is known as esterification. In a condensation reaction, two molecules join and produce a larger molecule whilst eliminating a small molecule. During esterification, this small molecule is water.

Alcohol + carboxylic acid (reversible arrows) ester + water

Question 3

What are esters used for?

Answer 3

• Flavourings
• Perfumes
• Solvents

Question 4

How would you break an ester?

Answer 4

The breaking up of an ester can be achieved by heating the ester with an alkali such as sodium hydroxide. This is an example of a hydrolysis reaction (the opposite of a condensation reaction) as a water molecule is added and breaks up the structure.

Question 5

What is the role of fats and oils in the body?

Answer 5

Used in our diets to provide us with energy. They play an important role in the transport of vitamins which are soluble in fats around the human body.

Question 6

What are fats and oils and how are they formed?

Answer 6

They are naturally occurring esters formed from reversible condensation reactions between the alcohol glycerol and different long chain carboxylic acids (fatty acids). The acid molecules can either be saturated or unsaturated. The fats and oils formed are also known as triglycerides. For one mole of glycerol used, three moles of fatty acids are required.

Question 7

What is the systematic name of glycerol?

Answer 7

Propane-1,2,3-triol

Question 8

What happens to the number of hydrogen atoms for each double bond added?

Answer 8

The number of hydrogen atoms decreases by two.

Question 9

What are fats?

Answer 9

• Solid at room temperature.
• Have higher melting points than oils as the fatty acids have the ability to pack closely together due to them not being distorted and being straight instead.
• Have more intermolecular forces.
• More energy is required to break them apart.

Question 10

What are oils?

Answer 10

• Liquid at room temperature.
• Have lower melting points than fats as the fatty acid chains contain double C=C bonds, distorting their shape and making them unable to pack closely together.
• Have less intermolecular forces.
• Less energy is required to break them apart.