Question

What will be the molarity of the solution in which 0.365 g of HCl gas is dissolved in 100 mL of solution?
(A) 2 M
(B) 0.2 M
(C) 1 M
(D) 0.1 M

Answer 1

Hint: An attempt to this question can be made by understanding the concept of molarity. Try to identify the composition of solute and solution in a standard solution. By this, you can devise an equation relating molarity to solute and solution. The formula to find molarity is however mentioned below:
$\text{M = }\dfrac{\text{n}}{\text{V}}$
Where,
$M$ is the molarity of the solution
$n$ is the number of moles of solute
$V$ is the volume of the solution in litres

Complete step by step solution:
Molar concentration also is known as molarity is a measure of the concentration of a chemical species or substance, in particular of a solute in a solution. It is measured in terms of the amount of substance per unit volume of solution.
In chemistry, the most commonly used unit for molarity is moles per litre, having the unit symbol mol/L. This is also the SI unit representing molarity.
We will now calculate the molarity for HCl gas with the mass of solute mentioned in the question above.
Mass of HCl gas used = 0.365 g
Molar mass of HCl = 36.5
Volume of final solution = 100 mL
We will now substitute the values in the formula mentioned in the hint.
$\text{M = }\dfrac{\text{n}}{\text{V}}$
$\Rightarrow \text{M = }\dfrac{\dfrac{0.365}{36.5}}{0.1}\text{ = 0}\text{.1}$

We can conclude that the molarity of the solution in which 0.365 g of HCl gas is dissolved in 100 mL of solution is 0.1 M. Therefore, the correct answer is option (D).

Note: Always remember to convert the volume of the solution into litres before substituting into the formula for molarity. This will help avoid confusion as well as errors.