16: Salts and Neturalisation

Question 1

What is the definition of neutralisation?

Answer 1

Neutralisation is the combination of hydrogen ions and hydroxide ions (or oxide ions) to form water molecules.

Question 2

What is the ionic equation of the neutralisation of hydrochloric acid and sodium hydroxide solution?

Answer 2

H⁺(aq) + OH^-(aq) -> H₂O(l)

Question 3

What is the ionic equation of the neutralisation of dilute sulphuric acid and magnesium oxide?

Answer 3

2H⁺(aq) + MgO(s) -> H₂O(l) + Mg²⁺(aq)

Question 4

What are exothermic reactions?

Answer 4

Exothermic reactions are reactions that give out heat to the surroundings.

Question 5

Why is there a larger temperature rise for neutralisation reactions when the solutions are replaced by those with higher concentration?

Answer 5

There is a larger number of mole of reactants available. Therefore, the temperature change is larger.

Question 6

What is the definition of acid salt?

Answer 6

An acid salt is a salt formed by replacing only part of the hydrogen ions from an acid.

Question 7

What is the definition of normal salt?

Answer 7

A normal salt is a salt formed by replacing all of the hydrogen ions from an acid.

Question 8

Under what circumstance is an acidic salt formed?

Answer 8

An acidic salt is the product when a strong acid reacts with a weak alkali.

Question 9

Under what circumstance is an alkaline salt formed?

Answer 9

An alkaline salt is the product when a strong alkali reacts with a weak acid.

Question 10

Under what circumstance is an neutral salt formed?

Answer 10

A neutral salt is the product when a strong acid reacts with a strong alkali.

Question 11

What is the pH of the salt formed when a weak acid reacts with a weak alkali?

Answer 11

The pH is undetermined since the relative strength of the acid and alkali is unknown.

Question 12

What is the chemical formula of ammonium ethanoate?

Answer 12

CH₃COONH₄

Question 13

How are soluble salts that are not group I or ammonium salts prepared?

Answer 13

By reacting an insoluble metal, base, or carbonate with acid.
1. Add excess solid to the acid.
2. Filter off the remaining solid and collect the filtrate.
3. Heat the filtrate to concentrate the solution.
4. Cool the filtrate to allow crystallisation.
5. Filter, wash, and dry the crystals.

Question 14

How are group I salts and ammonium salts prepared?

Answer 14

By carrying out a titration.
1. Carry out a titration of acid against the alkali and record the titre.
2. Add the same volume of the acid to the same volume of alkali.
3. Heat the filtrate to concentrate the solution.
4. Cool the filtrate to allow crystallisation.
5. Filter, wash, and dry the crystals.

Question 15

How are insoluble salts prepared?

Answer 15

By mixing solutions of 2 soluble salts and forming a precipitation reaction.
1. Mix the two solutions of soluble salts.
2. Filter off the precipitate, which is the desired salt.
3. Filter, wash, and dry the precipitate.

Question 16

List 4 uses of neutralisation.

Answer 16

1. Soil treatment: calcium oxide is used to reduce soil acidity, and ammonium sulphate used to reduce soil alkalinity.
2. Effluent and waste water treatment: slaked lime is used to neutralise acidic waste from factories.
3. Production of ammonium salts as fertilisers
4. Antacid: it neutralises hydrochloric acid in the stomach and relieves symptoms of indigestion.