Question

Molarity of a given orthophosphoric acid solution is 3M. Its normality is –
A. 9 N
B. 0.3 N
C. 3 N
D. 1 N

Answer 1

Hint- To solve this question, we use the basic formula related to Normality. As we know, Normality of the acidic solution is defined as the product of molarity and basicity (n-factor) of the given solution and in this case, we have orthophosphoric acid solution i.e. ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}$.

Formula used-
Molarity = $\dfrac{{{\text{Normality}}}}{{{\text{basicity}}}}$
Normality = molarity $\times$ basicity

Complete step-by-step answer:
As given in question,
Molarity = 3M
Remember, ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}$ has 3 -OH bond and only One -H bond so it is tribasic acid.
Similarly, ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}$ has 2 -OH bond and one -H bond so it is dibasic acid.
We have orthophosphoric acid solution,
And we know the chemical formula of orthophosphoric acid is ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}$.
Basicity of ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}$ acid refers to the number of replaceable hydrogen atoms in one molecule of the acid. As you can see in the structure of ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}$, there are 3 OH's attached. Thus, the basicity of ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}$ acid is also 3.
So, in ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}$, there are 3 such H's.
Now, using formula:
Normality = molarity $\times$ basicity
= 3 $\times$ 3
= 9 N
Therefore, option (A) is the correct answer.

Additional information-
Acidity is the extent to which a substance will donate a proton/hydrogen ion. Substances with high acidity will donate a proton easily while substances with low acidity will rarely donate protons and in presence of more acidic substances, accept a proton. For example, hydrochloric acid will easily donate protons to water while basicity is the extent to which a substance will accept a proton/hydrogen ion.

Note- Always remember the molarity of a solution is always less than its normality. Like normality, molarity is a unit of concentration in chemistry. And similarly, it is defined as the number of moles of solute per liter of solution. Sometimes, it is also known as molar concentration. And also, it is often used in the calculation of pH.
Molarity = $\dfrac{{{\text{Normality}}}}{{{\text{basicity}}}}$