Question

10 g of $\text{Mn}{{\text{O}}_{\text{2}}}$ on reaction with conc. HCl liberated 0.1 equivalent of $\text{C}{{\text{l}}_{\text{2}}}$ (molecular weight of $\text{Mn = 55 g/mol}$). Hence, percentage purity of $\text{Mn}{{\text{O}}_{\text{2}}}$ is:
a.) 87.0
b.) 21.75
c.) 50.0
d.) 43.5

Answer 1

Hint: Before solving the numerical, we should know that the physical properties of a substance can be used to establish its purity. The properties can include the melting point and the boiling point. Keeping all this fact in mind, we can go forward and solve the numerical.

Formula used: $\text{Percentage purity of a substance = }\left( \dfrac{\text{Mass of the pure chemical}}{\text{Total mass of the sample}}\text{ } \right)\text{ }\\!\\!\times\\!\\!\text{ 100}$

Complete step by step solution:
The balanced chemical reaction of the $\text{Mn}{{\text{O}}_{\text{2}}}$ on reaction with conc. HCl liberating 0.1 equivalent of $\text{C}{{\text{l}}_{\text{2}}}$. Since, HCl contains a single atom of Chlorine, 0.1 equivalent of Chlorine molecule is divided into two parts because of the diatomic nature of chlorine. Therefore, it corresponds to $\dfrac{\text{0}\text{.1}}{\text{2}}\text{ = 0}\text{.05}$ moles of chlorine.
10g sample contains 0.05moles of $\text{Mn}{{\text{O}}_{\text{2}}}$ or \text{0}\text{.5 }\\!\\!\times\\!\\!\text{ 86}\text{.9 }\\!\\!\times\\!\\!\text{ 4}\text{.35g}$$$$\text{Mn}{{\text{O}}_{\text{2}}}.
Therefore, the percentage purity of sample $\text{= }\dfrac{\text{4}\text{.35}}{\text{10}}\text{ }\\!\\!\times\\!\\!\text{ 100 = 43}\text{.5 }\\!\\!$
Therefore, the answer is 43.5%. Hence the correct answer is Option D.

Here is the equation:
$\text{Mn}{{\text{O}}_{2}}\text{ + HCl }\xrightarrow{{}}\text{ C}{{\text{l}}_{2}}\ \text{+ MnC}{{\text{l}}_{2}}\text{ + }{{\text{H}}_{\text{2}}}\text{O}$

Note: We should also know other ways by which purity of a solution can be determined.
As we know, different substances tend to have different melting and boiling points. And any pure substance will have a specific melting and boiling point. Boiling points and melting points of a substance tends to change with impurities.
One of the simplest ways to check the purity of a substance is to compare the substance with the certified pure sample. Even physical comparison can reveal a lot about the purity of a sample.
For the purity of solid substance, we need to check the melting point of solids. Pure solids will have a sharp and fixed melting point. Impure solids have lower and variable melting point due to the presence of impurity.