Question

The density of a solution containing 40% by mass of HCl is 1.2g/mL. Calculate the molarity of the solution.
a.) 11.15 M
b.) 12.15 M
c.) 13.15 M
d.) 14.15 M

Answer 1

Hint: “Molarity is a unit, used to express the concentration of a solution. Also known as molar concentration, molarity is the number of moles of solute (the chemical dissolved) per liter of solution”. It is denoted with a symbol “M” or “C”.

Complete step by step answer:
In the question it is given that the mass of HCl = 40 %
It is given that the mass of solution = 100 g
It is given that the density of the solution= 1.2 g/mL
The Molecular weight of HCl = 1+35.5 = 36.5 g
Now by using the above data we have to calculate the molarity of the hydrochloric acid solution.
\[\begin{align}
 & \text{Molarity=}\dfrac{\text{Percentage by mass }\!\!\times\!\!\text{ density }\!\!\times\!\!\text{ 10}}{\text{molecular weight of HCl}} \\
 & \text{ = }\dfrac{\text{40}\times \text{1}\text{.2}\times \text{10}}{36.5} \\
 & \text{ = 13}\text{.15 mol/lit} \\
\end{align}\]
Therefore the molarity of the hydrochloric acid solution is 13.15 mol/lit.
So, the correct answer is “Option C”.

Additional Information:
Mole/liter is the unit to measure the molarity of the solution.
Mole/kg is the unit to measure molality of the solution.
Molarity and molality of a solution having a particular concentration aren't the same.
The molality of a given solution is always greater than the molarity.

Note: Don’t be confused with the words molarity and molality.
Molarity- molarity is the number of moles of solute (the chemical dissolved) per liter of solution.
Molality- “Molality, also called molal concentration, is a measure of the concentration of a solute in the given solution in terms of amount of substance in a specified amount of mass of the solvent”.