Question

Calculate the equivalent weight of sulphuric acid:
$\;\left( {H = 1,S = 32,O = 16} \right)$
A.39 u
B.44 u
C.23 u
D.49 u

Answer 1

Sulphuric acid having the molecular formula ${H_2}S{O_4}$ . Equivalent weight is given by the following equation:
Equivalent weight of an acid = Molar mass/Number of replaceable hydrogen atoms.

Complete step by step answer:
Here the molecular formula is ${H_2}S{O_4}$ . Molecular mass is the sum of the atomic masses of elements present in a molecule.
Here the atoms are Hydrogen, Sulphur and oxygen having mass 1, 32 and 16 respectively.
Here 2 hydrogens are present. So, we have to multiply the mass of hydrogen by 2.
Similarly, here we have 4 Oxygen atoms, so we have to multiply the mass of oxygen by 4.
So, the molar mass of Sulphuric acid is $2 \times 1 + 32 \times 1 + 164 = 98$ .
In sulphuric acid 2 replaceable hydrogen atoms are present. So, we have to divide the molar mass by 2.
Equivalent weight= $\dfrac{{98}}{2}$
Equivalent weight= 49 u
Hence the correct answer is D, i.e 49 u.

Note: Students may confuse atomic mass and molecular mass. Atomic mass of an element is the number that expresses how many times the mass of an atom of the element is greater than $\dfrac{1}{{12}}$ th the mass of $^{12}C$ atom. Molecular mass is the sum of atomic masses of elements in the compound. For ionic compounds we are using formula mass. In ionic compounds positive and negative ions are arranged in a three-dimensional structure. So, we can calculate only formula mass. It is the sum of the average atomic masses of all the atoms in the compound.
Equivalent mass of a base= Molar mass/ Number of replaceable $O{H^ - }$ .