Question

2N HCl solution will have same molar concentration as:
(A) ${{4N }}{{{H}}_{{2}}}{{S}}{{{O}}_{{4}}}$
(B) ${{0}}{{.5N }}{{{H}}_{{2}}}{{S}}{{{O}}_{{4}}}$
(C) ${{1N }}{{{H}}_{{2}}}{{S}}{{{O}}_{{4}}}$
(D) ${{2N }}{{{H}}_{{2}}}{{S}}{{{O}}_{{4}}}$

Answer 1

Normality is the gram equivalent weight of solute per solution. Molarity is the number of moles of a compound dissolved in an amount of solvent. We should be knowing the relation between normality and molarity for conversion of the given normalities to molarity and comparing it with the HCl solution.

Complete step by step answer:
Normality of a compound, ${{N}}$ can be calculated by equivalent weight, ${{E}}$ by volume, ${{V}}$
${{N = }}\dfrac{{{E}}}{{{V}}}$
The relation of normality with molarity, ${{M}}$ is normality, ${{N}}$ by z-factor, ${{z}}$
${{M = }}\dfrac{{{N}}}{{{z}}}$
Z – factor is different for different classes of compounds. For acids the z – factor is the basicity of that acid as to the number of protons it furnishes in aqueous medium , for bases the z – factor is the acidity of the base as to number of hydroxide ion it furnishes in aqueous medium , for ions the charge the ion carrying is the z – factor .
Now we will calculate molarity of HCl by the above given formula
Molarity of ${{2N}}$ ${{HCl}}$, ${{{M}}_{{{HCl}}}} = \dfrac{2}{1} = 2{{M}}$
Now we will calculate the molarity of all four options and compare the molarity with the HCl molarity
(A) The molarity of ${{4N }}{{{H}}_{{2}}}{{S}}{{{O}}_{{4}}}{{ = }}\dfrac{{{4}}}{{{2}}}{{ = 2M}}$
(B) The molarity of ${{0}}{{.5N }}{{{H}}_{{2}}}{{S}}{{{O}}_{{4}}}{{ = }}\dfrac{{{{0}}{{.5}}}}{{{2}}}{{ = 0}}{{.25M}}$
(C) The molarity of ${{1N }}{{{H}}_{{2}}}{{S}}{{{O}}_{{4}}}{{ = }}\dfrac{{{1}}}{{{2}}}{{ = 0}}{{.5M}}$
(D) The molarity of ${{2N }}{{{H}}_{{2}}}{{S}}{{{O}}_{{4}}}{{ = }}\dfrac{{{2}}}{{{2}}}{{ = 1M}}$
On comparing the molarities of options with molarity of HCl it is iso – molar with ${{4N }}{{{H}}_{{2}}}{{S}}{{{O}}_{{4}}}$

So, the correct answer is Option A.

Note: The molarity and molality are often confused and mixed. The molarity is the number of moles in one liter of solution while molality is the number of moles present in one liter of solvent only so we have to subtract the mass of solute from the solution to get volume of solvent. For calculation of ${{pH}}$we use normality instead of molarity so that we don’t have to convert the moles for the number of protons or hydroxide produced in solution because there is a chance of calculation mistake.