Question

Define molarity and molality, and give its difference.

Answer 1

Hint: The factors from which we can calculate the molarity of the solution are moles of the solute and volume of the solution in liters. The factors from which we can calculate the molality of the solution are moles of the solute and mass of the solvent in kg.

Complete answer:
We know that the solution is made up of two components, the larger one solvent, and the smaller one solute. So the concentration of the solution or the concentration of the solute in the solution is expressed in many terms. And molarity and molality are used to find the concentration of the solution.
Molarity: We can define the molarity of the solution as the ratio of the moles of the solute to the volume of the solution in liters. The formula is given below and it is denoted with ‘M’:
$Molarity=\dfrac{\text{Moles of the solute}}{\text{Volume of the solution in L}}$
Molality: We can define the molality of the solution as the ratio of the moles of the solute to the mass of the solvent in kg. The formula of the molality is given below and it is denoted with ‘m’:
$Molality=\dfrac{\text{Moles of the solute}}{\text{Mass of the solvent in kg}}$
The difference between molarity and molality is that in molarity the concentration is calculated in the volume of the solution and in molality the concentration is calculated in the mass of the solvent. Molarity is $moles/liter$ and the molality is $moles/kg$.
The change in temperature and pressure of the solution affects the molarity of the solution, but there is no change in the molality of the solution.

Note:
While calculating, the molality of the solution is more accurate than the molarity of the solution. For calculating the moles of the solute, divide the given mass of the solute by the molecular mass of the solute.