Question

The unit of molality is.
A. $Mol/L$.
B. $L/Mol$.
C. $Mol/Kg$.
D. $K$.

Answer 1

We know that Molality is used to indicate the concentration of a solute in a solution and it mostly depends on the mass of the solvent. Molality is also referred to as molal concentration. It is usually denoted by the letter "m".

Complete step by step answer: Now, we see the definition of Molality.
The number of moles of solute in a kilogram of solvent is defined as the molality of the solution. Moles per kilogram $\left( {mol/kg} \right)$ are the SI unit of molality.
The mathematical expression of molality is,
$Molality{\text{ }}\left( m \right){\text{ }} = {\text{ }}\dfrac{{moles{\text{ }}of{\text{ }}solute\left( {Mol} \right)}}{{kilograms{\text{ }}of{\text{ }}solvent\left( {Kg} \right)}}{\text{ }}$
If the solution contains more than one solvent, we have to consider the molality of the mixed solvent, the units have to be expressed in such cases as mole solute per kilogram of mixed solvent.
Therefore, option C is correct.

Additional Information: Advantages and Disadvantages of Using Molality:
The advantage of using molality as a measure of concentration is that molality is only dependent on the mass of solute and the solvent which that molality is not affected by changes in temperature or pressure.
The disadvantage of molality is, it is not valid in cases where there is no pure substance in a mixture. Mixtures such as water and alcohol or alloys is an example..

Note: Don't confuse the terms of molality and molarity. The number of moles of solute in one liter of solution is defined as the molarity.
The mathematical expression of molarity is,
$Molarity{\text{ }}\left( M \right){\text{ }} = {\text{ }}\dfrac{{moles{\text{ }}of{\text{ }}solute\left( {Mol} \right)}}{{Solvent\left( L \right)}}{\text{ }}$
Remember, molality is used to measure the moles to the mass of the solvent and not with the mass of the solution.