TAE: Acids and pH

Question 1

Define acids as proton donors and describe the ionisation of acids in water

Answer 1

Acids are proton-donors.

In water, acids ionise, releasing a proton and a negative ion. The proton H+, can attach to a water molecule to form the hydronium ion H3O+

Question 2

Identify what Acetic acid is

Answer 2

Systematic name: Ethanoic acid

Molecular formula: CH3COOH

– It is the weak acid present in vinegar.

Question 3

Identify what Citric acid is

Answer 3

Systematic name: 2-hydroxypropane-1,2,3- tricarboxylic acid

Molecular formula: C6H8O7

– It is a triprotic acid, and is weak as it only
partially ionises in water. It occurs in citrus fruit (e.g. lemons, limes) and is widely used as a food additive.

Question 4

Identify what sulfuric acid is

Answer 4

Molecular formula: H2SO4

– It is a strong acid used to make batteries, fertilisers,
ethanol, etc. and is the most industrially produced
chemical.
– It is also found in acid rain.

Question 5

Identify what hydrochloric acid is

Answer 5

Molecular formula: HCL

– It is a strong acid that is produced in the stomach to
aid in digestion. Industrially, it is made in large quantities

Question 6

What is a strong acid?

Answer 6

A strong acid is one in which acid molecules have completely ionised. There are no neutral acid molecules present. Ionisation reaction with water goes to completion

Question 7

What is a weak acid?

Answer 7

A weak acid is one in which acid molecules have partially ionised. Some molecules remain intact in solution. The ionisation reaction of a weak acid with water is an equilibrium reaction that does not go to completion:

Question 8

What is a concentrated solution?

Answer 8

high molarity of acid particles per unit volume of solution.

Question 9

What is a dilute solution?

Answer 9

low molarity of acid particles per unit volume of solution.

Question 10

Explain the use of acids as food additives

Answer 10

Acids are used as food preservatives as lowering the inhibits enzymatic activity and prevents the growth of microbes which can spoil the food.
eg. Acetic acid (vinegar)
Citric acid- - jams

Acids are also used as flavour enhancers due to their sharp, sour taste (tartness).
eg. carbonic acids to add “fizz”

Question 11

Identify examples of naturally occurring acids and base, and their chemical composition

Answer 11

Natural acids

• HCL - lining of stomachs –> digestion of food
• Citric acid - citrus fruit

Natural bases:

• Ammonia - stale urine of animals
• Calcium carbonate - limestone