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

As we know that the formula hydrochloric acid is $HCl$ and $N{a_2}C{O_3}$ is sodium carbonate. Hydrochloric acid is acid and sodium carbonate is base. Acid reacts with base to form products with salt. $HCl$ is strong inorganic acid and protonated acid. $N{a_2}C{O_3}$ is an inorganic base and it is a mild base.

Formula used:
We need to know that the molecular mass of the compound is defined as the sum of the atomic mass of the atom present in the molecules.
The equivalent mass of the molecule in titration is defined as the total molecular mass of the reactant divided by the number of hydrogen reactants to replace in a molecule by reaction.
Equivalent mass of molecules $= \dfrac{{{\text{Molecular mass}}}}{{{\text{Number of hydrogen with reactant}}}}$

Complete step by step answer:
The entire reaction of sodium carbonate reacts with hydrochloric acid to form sodium bicarbonate and sodium chloride.
$N{a_2}C{O_3} + HCl \to NaHC{O_3} + NaCl$
The molecular mass of the $N{a_2}C{O_3}$ is calculated,
Two sodium atoms, one carbon atom and three oxygen atoms are present in $N{a_2}C{O_3}$ molecules.
The atomic mass of sodium = $23g$
The atomic mass of carbon = $12g$
The atomic mass of oxygen = $16g$
The molecular mass of $N{a_2}C{O_3}$ ,
$= \left( {2 \times 23} \right) + 12 + \left( {3 \times 16} \right)$
$= 46 + 12 + 48$
On adding we get,
$= 106g$
One hydrogen is reacted in reaction between hydrochloric acid and sodium bicarbonate.
The equivalent mass of $N{a_2}C{O_3}$ is calculated as,
Equivalent mass of $N{a_2}C{O_3} = \dfrac{{{\text{Molecular mass of }}N{a_2}C{O_3}}}{{{\text{Number of hydrogen react with }}N{a_2}C{O_3}}}$
On substituting the known values we get,
$= \dfrac{{106}}{1}$
Equivalent mass of $N{a_2}C{O_3} = 106$

So, the correct answer is Option A.

Note: We must have to remember that the acids are proton donors. Bases are proton acceptors. In this reaction, sodium bicarbonate $N{a_2}C{O_3}$ acts as base and $HCl$ act as acid. $N{a_2}C{O_3}$ accepts the proton from acid to form $NaHC{O_3}$ and form $NaCl$. The equivalent mass is one of the important factors for neutralisation of acid and base in the titration. When acid and base reaction occurs, release of a huge amount of energy is considered as an exothermic reaction.