Question

The unit of molarity is $mol\,li{{t}^{-1}}$.
(A) True
(B) False

Answer 1

Hint: Molarity of a solution defined as the number of moles of a solute dissolved per liter of solution. It is given as
\[\text{Molarity = }\dfrac{\text{number of moles of solute}}{\text{volume of solution (in L)}}\]
Number of moles, n of solute is calculated as
     \[\text{n = }\dfrac{\text{mass of solute (in grams)}}{\text{molar mass of solute}}\]

Complete step by step answer:
As we know that molarity is the number of moles dissolved in one liter of the solution.
Number of moles , n is expressed in mol.
Volume of the solution, V is taken in liters.
The mathematical expression of molarity is
     \[\text{Molarity = }\dfrac{\text{n (in mol)}}{\text{V (in liter)}}\]
The unit of molarity is clearly moles per liter.

Also, we can confirm this by using the expression for the number of moles of a solute. The number of moles of solute in a solution is calculated by dividing the mass of solute present in the solution by the molar mass of the solute.
Mass of solute, present in solution is expressed in grams.
Molar mass, m is the mass of one mole of the solute and its unit is grams $mo{{l}^{-1}}$.
If volume of solution, V is taken in ml, the expression for molarity becomes
     \[\text{Molarity = }\dfrac{\text{w (in grams)}}{\text{m (in grams mo}{{\text{l}}^{\text{-1}}}\text{)}}\text{ }\!\!\times\!\!\text{ }\dfrac{\text{1000 ml liter}{{\text{e}}^{-1}}}{\text{V (in ml)}}\]
We can see form the above equation that the unit of molarity is $mol\,li{{t}^{-1}}.$
So, the correct answer is “Option A”.

Additional Information:
The concentration of a solution can be expressed in terms of normality (N), molarity (M) and molality (m).
If a solution is diluted, its molarity decreases. Molarity is temperature dependent and decreases with rise in temperature. It is due to the fact volume increases with increase in temperature.

Note: It is to be noted here that $mol\,li{{t}^{-1}}$ is the most commonly used unit of molarity. The S.I unit of molarity is $mol\,{{m}^{-3}}$. As 1liter = 1000 ${{m}^{3}}$ then, unit of molarity can be converted from $mol\,li{{t}^{-1}}$to $mol\,{{m}^{-3}}$ using the relation $1mol\,li{{t}^{-1}}={{10}^{3}}mol\,{{m}^{-3}}$.