4.2 Reactions of acids

Question 1

What is
oxidation / reduction?

Answer 1

Oxidation - When a substance gains oxygen

Reduction - When a substance loses oxygen

Question 2

How are oxidation and reduction defined in terms of
electron transfer ? (Higher)

Answer 2

Oxidation – loss of electrons

Reduction – gain of electrons

Question 3

What is the general equation for a reaction between metals and acids? What type of reaction is
this?

Answer 3

Metal + acid → salt + hydrogen

Redox reaction, also a displacement reaction

Question 4

Which metals in the reactivity
series will react with acid?

Answer 4

Those above hydrogen

Question 5

What is the general equation for a neutralisation reaction?

Answer 5

Base + acid → salt + water

Question 6

What is the general equation for the reaction between metal
carbonate and acid?

Answer 6

Metal carbonate + acid → salt + water + carbon dioxide

Question 7

What is the general equation for the reaction between metal oxides and acids?

Answer 7

Metal oxide + acid → a salt + water

Question 8

What is a redox reaction? (Higher)

Answer 8

A reaction where both oxidation and reduction occurs

Question 9

Explain in terms of gain or loss of
electrons which element has been
oxidised and which element has been reduced when magnesium reacts with
hydrochloric acid. (Higher)

Answer 9

Magnesium has lost electrons and thus has been oxidised (Mg to Mg2+)

The hydrogen in HCl has gained electrons and thus has been reduced (H+ to H2)

Question 10

How is a soluble salt formed?

Answer 10

● React the excess acid with some insoluble chemical (e.g. metal oxide)

● Filter off the leftovers

● Crystallise the product

Question 11

What do acids and alkalis produce in aqueous solutions?

Answer 11

Acids produce hydrogen ions, alkalis produce hydroxide ions

Question 12

What are bases, acids and
alkalis?

Answer 12

Bases are compounds that neutralise acids, acids produce hydrogen ions in
aqueous solutions, alkalis are soluble bases - produce hydroxide ions in aqueous solutions

Question 13

What is the pH scale and what
does a pH of 7 show?

Answer 13

The measure of acidity/alkalinity of a solution. A pH of 7 is a neutral solution.

Question 14

State the general equation for a
neutralisation reaction in a short,
ionic form.

Answer 14

OH− + H+→ H2O

Question 15

What is a strong acid? What is
a weak acid? (Higher)

Answer 15

Strong acids are completely ionised in an aqueous solution. Weak acids are only partially ionised in an aqueous solution.

Question 16

What happens to pH as the concentration of H+ increases? (Higher)

Answer 16

The pH decreases

Question 17

What is a concentrated acid and what is a dilute acid? Is this the same as a strong and weak acid? (Higher)

Answer 17

● Concentrated acid has more moles of acid per unit volume than dilute (dilute refers to solutions of low concentrations)

● It is not the same - concentration is not the same thing as the strength of an acid.

● Strength refers to whether the acid is completely ionised in water (strong) or
only partially (weak).

Question 18

As the pH is decreased by one
unit, what change is seen in the
hydrogen ion concentration? (Higher)

Answer 18

Increases by a factor of 10

Question 19

Name the following salts:
LiNO3, K2CO3, MgBr2, BaSO4

Answer 19

● Lithium nitrate

● Potassium carbonate

● Magnesium bromide

● Barium sulfate