Question

Give one example of a combination reaction that is a redox reaction and another that is not a redox reaction.

Short answer

You need to provide one example of a combination reaction that is a redox reaction and another that is not a redox reaction.

Step-by-step solution

Solution of the problem

Reaction of metal and non-metal forms an ionic compound is an example of redox combination reaction.

Reaction of metal oxide with water forms an acid is an example of normal combination reaction.

Redox combination reaction

Reaction of metal and non-metal forms an ionic compound is an example of redox combination reaction.

Example:

$2Mg\left(g\right)+O_2\left(g\right)\to 2MgO\left(g\right)$

Explanation of the solution

Oxidation no of element Magnesium and oxygen is 0.

Oxidation no of oxygen in MgO is -2 and magnesium is +2.

The oxidation no of oxygen is 0 in O₂ decreases to -2 in MgO. Therefore, O₂ undergoes reduction.

The oxidation no of magnesium is 0 in Mg increases to +2 in MgO. Therefore, Mg undergoes oxidation.

Normal combination reaction

Reaction of metal oxide with water forms an acid is an example of normal combination reaction.

Example:

$CaO\left(s\right)+H_{2}O\left(l\right)\to Ca{\left(OH\right)}_2\left(aq\right)$

Explanation of the solution

Oxidation no of oxygen in CaO is -2.

Oxidation no of calcium in CaO is +2.

Oxidation no of oxygen in Ca(OH)₂ is also -2.

Oxidation no of calcium in Ca(OH)₂ is also +2.

The oxidation no of oxygen and calcium doesn’t change in the whole reaction. Hence, it is not a redox reaction; it is a normal combination reaction.