Question

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

Answer 1

Firstly to understand, equivalent weight concept, we need to know and understand that 2 key terms- atomic or molecular weight and Valency or it is also called n-factor.
Calcium is a metal of s-block, 3rd period and 2nd group called alkaline earth metals. So, from an element's position, we can find the valency or combining capacity.

Complete step by step answer:

Here, in this case we have Calcium metal, so we will need atomic weight of calcium. We know that atomic weight of calcium is 40gm.
And, the second factor needed is valency or n-factor. As we know that calcium is second group element, alkaline earth metal, so the valency is 2, as alkaline earth metals have outer electronic configuration of 2, so they can donate these 2 electrons to become bivalent cation, $C{a^{2 + }}$
Now, thus we can calculate equivalent weight by using below formula:
$E = \dfrac{M}{{n - factor}}$
Here, E=Equivalent weight
M=Atomic or molecular weight= 40 gm
n-factor = valency = 2
Now, substitute the values in above formula, we get
$E = \dfrac{{40}}{2}$
E=20 gm
Thus the correct option is (D) 20

Additional Information: The actual definition of equivalent weight is the mass of any substance which combines or displaces 1 gram of Hydrogen, 8 grams of Oxygen or 35.5 grams of Chlorine. But in our day today calculation and usage, we can use the formula directly which is mentioned above. Sometimes, when an unknown substance is given then we may have to use basic definition, and compare equivalent weight and get the molecular weight of the given substance.

Note:
Equivalent weight is molecular weight divided by valency of n-factor, whereas number of gram equivalents is Molecular weight divided by equivalent weight. Also in chemistry, the words ‘weight’ and ‘mass’ are the same, which can be used interchangeably.