Normality And Equivalent Concept

Question

A 250 mL solution contains 4.9 g of sulfuric acid ($\text{H}_2\text{SO}_4$). What is the normality of this solution? (Molar mass of $\text{H}_2\text{SO}_4 = 98$ g/mol; $n$-factor for $\text{H}_2\text{SO}_4$ in acid-base reaction = 2)

RankGuru · Accepted Answer

Normality is defined as the number of gram equivalents of solute dissolved per litre of solution. The gram equivalent mass (equivalent weight) of an acid is its molar mass divided by the n-factor (basicity or number of replaceable protons). For $\text{H}_2\text{SO}_4$, equivalent weight $= 98/2 = 49$ g/eq. Gram equivalents in 4.9 g: $n_{\text{eq}} = 4.9/49 = 0.1$ equivalents. Volume $= 250 \, \text{mL} = 0.250$ L. Normality $N = 0.1/0.250 = 0.4$ N. Alternatively, normality $= \text{molarity} \times n\text{-factor}$. Molarity $= (4.9/98)/0.250 = 0.05/0.250 = 0.2$ M. Normality $= 0.2 \times 2 = 0.4$ N. Option 0.2 N is the molarity, not the normality — the n-factor of 2 has not been applied. Option 0.5 N would require 6.125 g of $\text{H}_2\text{SO}_4$ in 250 mL, not 4.9 g. Option 1.0 N would require 12.25 g in 250 mL. Normality is particularly important in acid-base titrimetry and is a higher-order concept tested in JEE Advanced. Plausibility check: since $N = M \times n$-factor $= 0.2 \times 2 = 0.4$ N, and normality must always be $\geq$ molarity for polyprotic acids, 0.4 N $>$ 0.2 M is consistent.

Normality And Equivalent Concept

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