Question

Explain the following in terms of gain or loss of oxygen with two examples each. 
(a) Oxidation
(b) Reduction

Answer 1

(a) Oxidation is the gain of oxygen.
For example: 

In equation (i), H₂ is oxidized to H₂O and in equation (ii), Cu is oxidised to CuO.

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(b) Reduction is the loss of oxygen.
For example : 

In equation (i), CO₂ is reduced to CO and in equation (ii), CuO is reduced to Cu.

Answer 2

In terms of gain or loss of oxygen, oxidation and reduction can be explained as follows:

(a) Oxidation: Oxidation involves the loss of electrons or an increase in oxidation state. When a substance undergoes oxidation, it may also involve the gain of oxygen or the loss of hydrogen.

1. Example of Gain of Oxygen: The oxidation of iron metal to form iron oxide (rust) is a classic example.

\[4Fe + 3O_2 \rightarrow 2Fe_2O_3\]

Here, iron (Fe) is oxidized from an oxidation state of 0 to +3 in iron oxide (Fe2O3), indicating a gain of oxygen.

2. Example of Loss of Oxygen: The combustion of methane (CH4) is an example where methane is oxidized to produce carbon dioxide and water.

\[CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O\]

In this reaction, methane loses hydrogen and gains oxygen, leading to oxidation.

(b) Reduction: Reduction involves the gain of electrons or a decrease in oxidation state. In terms of oxygen, reduction often involves the loss of oxygen or the gain of hydrogen.

1. Example of Loss of Oxygen: The reduction of copper(II) oxide (CuO) using carbon monoxide (CO) to produce copper (Cu) and carbon dioxide (CO2).

\[CuO + CO \rightarrow Cu + CO_2\]

Here, copper(II) oxide loses oxygen to form copper, which is a reduction process.

2. Example of Gain of Oxygen: The oxidation of hydrogen gas (H2) to form water (H2O) is an example where oxygen is gained.

\[2H_2 + O_2 \rightarrow 2H_2O\]

In this reaction, hydrogen gains oxygen, leading to the formation of water, which is an oxidation process for hydrogen.