Question

Does molality depend on the temperature?

Answer 1

The concentration of a solution is the measure of the amount of solute which is dissolved in the given amount of solution. The solution which consists of a relatively large amount of dissolved solute is known as concentrated solution while the solution in which the amount of dissolved solute is relatively small is known as dilute solution.

Complete answer:
The concentration of a solution can be represented in the units of molarity, molality and normality which are defined as follows:
Molarity: It is the number of moles of the solute dissolved per litre of solution and it is denoted by ‘M’. The expression for molarity is given as follows:
$M = \dfrac{{{\text{number of moles of solute}}}}{{{\text{Volume of solution (L)}}}}$
The unit of Molarity is $mol{L^{ - 1}}$.
Molality: It is the number of moles of the solute dissolved in $1\;kg$ of solvent and it is denoted by ‘m’. The expression for molality is given as follows:
$m = \dfrac{{{\text{number of moles of solute}}}}{{{\text{mass of solvent (kg)}}}}$
The unit of Molality is $mol\;k{g^{ - 1}}$.
Normality: It is the gram equivalent of the solute dissolved per litre of solution and it is represented by ‘N’. The expression for normality is given as follows:
$N = \dfrac{{{\text{number of equivalents of solute}}}}{{{\text{Volume of solution (L)}}}}$
The unit of Normality is ${g_{eq}}{L^{ - 1}}$.
So, as per above definitions it is clear that the molality of a solution is independent of the volume of solution. It depends on the number of moles of solute and mass of solvent which does not change on varying the temperature. Therefore, on changing the temperature no variation in the value of molality will be observed.
Thus, we can conclude that the molality of the solution does not depend on the temperature.

Note:
Remember that both concentration units molarity and normality depend on the volume of temperature which shows variation on changing the temperature. So, molarity and normality depend on temperature while molality is independent of temperature. This is the major reason that the molality is preferred over molarity.