Question

Molar concentration of a solution of water is:
(a) Always equal to normality
(b) More than molality of the solution
(c) Equal to molality of the solution
(d) Less than molality of the solution

Answer 1

Hint : Molar concentration is also known as Molarity. Molar concentration is the total number of moles of the solute present in per litre of the solution. The unit of molar concentration is $mol/L$ or $M$ .

Complete Step By Step Answer:
First, we will define the terms Normality and Molality:
Normality: Normality can be defined as the measure of equivalent concentration in which normality is equal to gram equivalent weight per litre of the solution.
Molality: Molality is the measure of concentration in which molality is equal to number of moles of solute per kilogram of the solvent.
Now, moving forward to all the given options:
The first option, (a) Always equal to normality
The number of equivalents and the number of solutes are the same sometimes and the volume of the solution is also the same. Hence, sometimes the molarity and normality are the same and sometimes they are not always equal to the normality.
Now, moving the second option, (b) More than molality of the solution
In molality and molarity, the number of solutes are the same. But the volume of solution is greater than the weight of the solvent. Hence, the molarity is not more than molality
Now, moving the third option, (c) Equal to molality of the solution
In molality and molarity, the number of solutes are the same. But the volume of solution is greater than the weight of the solvent. Hence, the molarity is not equal to molality.
Now, moving the fourth option, (d) Less than molality of the solution
In molality and molarity, the number of solutes are the same. But the volume of solution is greater than the weight of the solvent. Hence, the molarity is less than molality.
Hence, Molar concentration of a solution of water is Less than molality of the solution.
Hence, the correct option is (d) Less than molality of the solution.

Note :
Molality is temperature independent whereas the molarity is temperature dependent because neither moles of solute nor mass of solvent is dependent on temperature, whereas the volume of the solution is dependent on temperature.