Question

Equivalent weight of calcium metal is:
(A) 12
(B) 24
(C) 36
(D) 20

Answer 1

Hint: Equivalent weight is the quantity of a substance that would exactly react with the fixed quantity of another substance in the particular reaction.
Only one option will be correct from all the given options.

Complete step by step solution:
Let us firstly see what we mean by equivalent weight;
Equivalent weight-
It is also known as gram equivalent. This would basically mean the mass of a given substance that would combine with the fixed quantity of another substance.
Equivalent weights can be stated as;
$Eq.weight=\dfrac{Mol.mass}{Valency}$ (for simple substances)
 Or
$Eq.weight=\dfrac{Mol.mass}{Acidity}$ (for basic reactions)
Or
$Eq.weight=\dfrac{Mol.mass}{Basicity}$ (for acidic reactions)
The equivalent weight of any substance can be calculated as the ratio of its molecular or atomic weight to the valency it possesses. It has the unit as mass specifically amu.
Illustration-
Atomic number of Calcium is 20. Thus, it has 2 valence electrons as stated by Bohr’s electronic configuration i.e. 2, 8, 8, 2.
The atomic weight of calcium is nearly 40 gm/mol.
Thus, using the above equation;
$Eq.weight=\dfrac{Mol.mass}{Valency}$ = $\dfrac{40}{2}=20$

Thus, the equivalent weight of calcium metal is 20. Therefore, option (D) is correct.

Note: Do note that the equivalent weight of a substance may vary with the type of reaction it undergoes (for acid-base reactions).
The number of equivalent weights of any substance dissolved in one litre of solution is called the normality of that solution. The number of equivalent weights or gram equivalents are given as the ratio of equivalent weight be the given mass of the substance i.e.
\[n=\dfrac{eq.wt.}{given-mass}\]