Question

Calculate the equivalent mass of $N{{a}_{2}}C{{O}_{3}}$ when it is titrated against $HCl$ in presence of phenolphthalein.
A) 106
B) 53
C) 26.5
D) 212

Answer 1

Hint: Equivalent mass or weight is not equal to molecular weight for all chemicals. The equivalent weight of a chemical is a proportional mass of chemical entities which combine or displace other chemical entities. Equivalent weight is going to be denoted with a symbol E.

Complete step by step answer:
In the question it is given that sodium carbonate ($N{{a}_{2}}C{{O}_{3}}$) is titrated with hydrochloric acid ($HCl$) in presence of phenolphthalein indicator.
We know that sodium carbonate has basic nature and hydrochloric acid acts as an acid.
Sodium carbonate reacts with hydrochloric acid and forms sodium bicarbonate and sodium chloride

$N{{a}_{2}}C{{O}_{3}}+HCl\xrightarrow{{}}NaHC{{O}_{3}}+NaCl$
In the above reaction, one mole of sodium carbonate reacts with one mole of hydrochloric acid and forms one mole of sodium bicarbonate and one mole of sodium chloride.
Equivalent mass = $\dfrac{\text{Molar mass}}{\text{Number of hydrogens added or removed}}$
The molar mass of sodium carbonate is 106. Substitute the molar mass in the above equation.
In the above reaction, one hydrogen is added to sodium carbonate.
Equivalent mass of sodium carbonate = $\dfrac{\text{106}}{\text{1}}=106$.

Therefore the equivalent mass of sodium carbonate is 106 for the given reaction.
So, the correct option is A.

Note: Don’t be confused with sodium carbonate and sodium bicarbonate. Both are not the same.
The molecular formula of sodium carbonate is $N{{a}_{2}}C{{O}_{3}}$.
The molecular formula of sodium bicarbonate is $NaHC{{O}_{3}}$.