Question

On dissolving $1\,mole$of each of the following acids in $1\,litre$water, the acid which does not give a solution of strength $1N$is
A.$HCl$ [MP PET$1993$]
B.Perchloric acid
C.$HN{{O}_{3}}$
D.Phosphoric acid

Answer 1

Hint: When one mole of any substance is dissolved in one $litre$ water is called molarity, which means here we have a $1M$solution and we have to convert them into a $1N$solution. As we know in the case of acids, molarity can be converted into normality by multiplying $n-$factors. So from the given acids, we have to find out $n-$ factor.

Formula Used:Normality of a solution,$N=$Molarity ($M$)$\times $$n-$factor

Complete answer:Molarity is the concentration of a compound or ion in solution and normality is the molar concentration of only acid or base component in the solution. Normality can be calculated by multiplying $n-$the factor or basicity of acid with the molarity of the solution.
Here we have four acids with the same or different $n-$factors. Let us check the normality of each given acidic solution. Here molarity of the solution$1\,mol/litre$
In (A), hydrochloric acid$HCl$ has the $n-$factor or basicity $1$as there are the no. of ${{H}^{+}}$ion$=1$
$HCl\rightleftharpoons {{H}^{+}}+C{{l}^{-}}$
$\therefore Strength=1\,mol/litre\times 1=1N\,$
In (B), perchloric acid with chemical formula $HCl{{O}_{4}}$is a monobasic acid and basicity $1$.
$HCl{{O}_{4}}\rightleftharpoons {{H}^{+}}+ClO_{4}^{-}$
$\therefore Strength=1\,mol/litre\times 1=1N\,$
Nitric acid,$HN{{O}_{3}}$ which is given in option (C) is also monobasic as it contains one ${{H}^{+}}$ion. So, basicity$=1$
$\therefore Strength=1\,mol/litre\times 1=1N\,$
In (D), phosphoric acid${{H}_{3}}P{{O}_{4}}$ is tribasic acid or basicity $3$as it has three ${{H}^{+}}$ions.
${{H}_{3}}P{{O}_{4}}\rightleftharpoons 3{{H}^{+}}+PO_{4}^{3-}$
$\therefore Strength=1\,mol/lit\times 3=3N$
So, by dissolving $1M$phosphoric acid in $1\,litre$ solution we cannot get a solution of strength $1N$.

Thus, option (D) is correct.

Note: Generally molarity can be converted into normality in acidic or basic solutions in different ways. When an acidic solution molarity is multiplied by the basicity of acid but in basic solution molarity is multiplied by the acidity of the base giving normality to that particular acidic or basic solution.