6092 Chapter 12 Redox 5 Change in Oxidation State

The term oxidation can be used to describe a reaction in which a reactant loses electrons to form a substance (product). When the reactant loses electrons, its oxidation state ​ (a)   . The reactant is said to be ​ (b)   .

• increases
• oxidised
• decreases
• reduced

Reduction is the reverse of oxidation. The term reduction can be used to describe a reaction in which a reactant gains electrons to form a substance (product). When the reactant gains electrons, its oxidation state ​ (a)   . The reactant is said to be ​ (b)   .

• decreases
• reduced
• increases
• oxidised

When heated copper reacts with oxygen, copper(II) oxide is produced.

2Cu(s) + O₂(g) → 2CuO(s)

oxidation state of Cu in Cu is ​ (a)  

Oxidation state of Cu in CuO is ​ (b)  

• 0
• +2
• -2
• 2

When heated copper reacts with oxygen, copper(II) oxide is produced.

2Cu(s) + O₂(g) → 2CuO(s)

oxidation state of O in O₂ is ​ (a)  

Oxidation state of O in CuO is ​ (b)  

• 0
• +2
• -2
• 2

When heated copper reacts with oxygen, copper(II) oxide is produced.

2Cu(s) + O₂(g) → 2CuO(s)

In term of oxidation state, which substance is oxidised?

When heated copper reacts with oxygen, copper(II) oxide is produced.

2Cu(s) + O₂(g) → 2CuO(s)

In term of oxidation state, which substance is reduced?

When heated copper reacts with oxygen, copper(II) oxide is produced.

2Cu(s) + O₂(g) → 2CuO(s)

Explain, in terms of oxidation states, why the reaction between copper and oxygen is a redox reaction.

Answer explanation

The oxidation state of copper increases from 0 in copper metal (Cu) to +2 in copper(II) oxide (CuO). Copper metal (Cu) is oxidised. OR Copper metal undergoes oxidation.

The oxidation state of oxygen decreases from 0 in oxygen gas (O₂) to -2 in copper(II) oxide (CuO). Oxygen gas (O₂) is reduced. OR Oxygen gas (O₂) undergoes reduction.

A substance (reactant) that causes the oxidation state of another reactant to ​ (a)   , itself undergoes ​ (b)   . This substance is known as ​ (c)  

• increase
• reduction
• oxidising agent
• decrease
• oxidation
• reducing agent

A substance (reactant) that causes the oxidation state of another reactant to ​ (a)   , itself undergoes ​ (b)   . This substance is known as ​ (c)  

• decrease
• oxidation
• reducing agent
• increase
• reduction
• oxidising agent

When heated copper reacts with oxygen, copper(II) oxide is produced.

2Cu(s) + O₂(g) → 2CuO(s)

In term of oxidation state, which substance is an oxidising agent?