Question

Identify the redox reaction among the following:
(A) Acid-base neutralization
(B) Precipitation reaction
(C) Metal displacement reaction
(D) All of the above.

Answer 1

Hint: To answer this, remember that gain of the electron is reduction and loss of electron is oxidation. A reaction where both oxidations, as well as reduction, takes place simultaneously is known as a redox reaction.

Complete step by step solution:
To answer this question, we have to understand what a redox reaction is.
A reaction where oxidation and reduction take place simultaneously is known as a redox reaction which is the abbreviation for a reduction-oxidation reaction. In a redox reaction, the transfer of electrons is identified by seeing the change in oxidation number of the species which are reacting.
Now, let us discuss the reactions given to us and determine whether they are redox reactions or not.
Firstly, we have an acid-base neutralization. In this reaction, acid and base react with each other and results in a neutral solution. In the solution, there is no excess hydrogen or hydroxide ions. There can be 4 types of acid-base neutralisation reactions based upon the relative strength of the acid and the base. However, in a neutralisation reaction, no transfer of electrons takes place and there is no change in oxidation states of the reactant species. So, this is not a redox reaction.
Then we have precipitation reactions. In this reaction, an insoluble precipitate is formed when two soluble salts are mixed in a solution. For a reaction to be redox, the number of electrons of the element i.e. the oxidation state must change. In a precipitation reaction, there is no change in the oxidation states so it is not a redox reaction.
And lastly, we have metal displacement reactions. It is a displacement reaction where the more reactive metal replaces the less reactive metal in its solution.
$$\stackrel{0}{Zn}(s)+\stackrel{+2}{Cu}\stackrel{+6}{S}\stackrel{-2}{O_4}(aq)\to \stackrel{+2}{Zn}\stackrel{+6}{S}\stackrel{-2}{O_4}(aq)+\stackrel{0}{Cu}(s)$$
Here we can see that the oxidation state of zinc changes from 0 to +2 and that of copper changes from +2 to 0. So, this is a redox reaction as both oxidation and reduction are taking place simultaneously.

Therefore, the correct answer is option (C) metal displacement reaction.

Note: A disproportionation reaction is a special case of a redox reaction. A disproportionation reaction is a redox reaction where the oxidation and reduction both take place from the same element/species and form two or more different products. If a compound forms two products, one as a result of oxidation and other as a result of the reduction, we can say it undergoes disproportionation.