Question

\[10\] millimoles of a di-acidic base exactly neutralize \[100\] mL of acid. Then the normality of that acid is:
A.\[0.2\] N
B.\[0.1\] N
C.\[0.4\] N
D.\[0.5\] N

Answer 1

Hint: The number of ionisable hydroxide ions which are present in one molecule of base is referred to as the acidity of the base. A di-acidic base on ionization will give two hydroxide ions. Normality is equal to the gram equivalents of a solute present per liter of solution.

Complete step by step answer:
In order to determine the normality of acid we have to determine the gram equivalent of the base. The given base is diacidic but the acid can be both monobasic and dibasic in nature. We have to separately calculate for monobasic and dibasic acid.
 Given,
Number of moles of base is equal to \[10\] millimoles = \[10 \times {10^{ - 3}}\] mol
The acidity of the base is \[2\].
The number of equivalence of base will be = number of moles of base X acidity of base
= \[10 \times {10^{ - 3}} \times {\text{ }}2\]
 = \[2 \times {10^{ - 2}}\]
Given the diacidic base has completely neutralized the base. Therefore, the number of equivalents of base is equal to the number of equivalences of acid.
The volume of acid used for neutralization is \[100\]mL. The volume of the acid in liters will be
\[V = \dfrac{{100}}{{1000}} = 0.1L\]
Hence the normality of the acid will be as follows:
\[N = \dfrac{{equivalence{\text{ }}of{\text{ }}acid}}{{volume{\text{ }}of{\text{ }}acid}}\]
\[N = \dfrac{{2 \times {{10}^{ - 2}}mol}}{{0.1L}}\]
\[N = 0.2\].
\[10\] Millimoles of a diacidic base will neutralize \[10\] millimoles of dibasic acid or \[20\] millimoles of a monobasic acid. Hence for a dibasic acid, \[10\] millimoles are present in \[100\] mL solution and for a monobasic acid, \[20\] millimoles are present in \[100\] mL solution. So the normality for dibasic or monobasic acid will be \[0.2\]N.

Note:
Normality should not be confused with morality. Molarity is also a measurement of the concentration of a solution. It is calculated as the moles of solute and not gram equivalents of solute present per liter of solution.