Question

What is the stoichiometric coefficient of Ca in the following reaction?
\[Ca+A{{l}^{3+}}\to C{{a}^{2+}}+Al\]
(A) 1
(B) 1.5
(C) 2
(D) 3

Answer 1

Hint: A redox reaction involves the simultaneous occurrence of both oxidation and reduction process. In oxidation, there is a loose of electrons and in reduction, there is a gain of electrons. The number of electrons lost will be equal to the number of electrons gained.

Complete step by step solution:
A redox reaction is balanced only when the electrons which are loose in the oxidation process are completely used in the reduction process.
Given the reaction in the question is:
\[Ca+A{{l}^{3+}}\to C{{a}^{2+}}+Al\]
Calcium is a divalent atom, calcium lose two electrons, the reaction involved is:
\[Ca\to C{{a}^{2+}}+2{{e}^{-}}\text{ --(1)}\]
And we know that aluminium is a trivalent atom, aluminium gain three electrons the reaction involved is: \[A{{l}^{3+}}+3{{e}^{-}}\to Al\text{ --(2)}\]
Since the oxidation and the reduction reaction occurs simultaneously we have to multiply equation (1) with 3 and equation (2) with 2, so that the number of electrons lost and gained in the reaction will be equal.
Multiply equation (1) with 3:
\[3Ca\to 3C{{a}^{2+}}+6{{e}^{-}}\text{ --(3)}\]
Multiply equation (2) with 2:
\[2A{{l}^{3+}}+6{{e}^{-}}\to 2Al\text{ --(4)}\]
Now we add equation (3) and equation (4), the answer will be:
\[3Ca+2A{{l}^{3+}}\to 3C{{a}^{2+}}+2Al\]
From the above reaction we can say that:
The stoichiometric coefficient of $Ca$ is = 3
The stoichiometric coefficient of $A{{l}^{3+}}$ is = 2
The stoichiometric coefficient of $C{{a}^{2+}}$ is = 3
The stoichiometric coefficient of $Al$ is = 2

Hence the correct answer is option (D).

Note: There are two methods which are used to balance oxidation-reduction reactions are oxidation number method and ion-electron method. In the ion-exchange method acidic, basic and neutral solutions are balanced using the hydrogen ion, hydroxide ion and water.