Question

What is the molal elevation constant? Derive its equation and give its unit.

Answer 1

Hint:The molal elevation constant is related to the elevation in the boiling point of a solvent. It can be derived in consideration with the molal concentration of solute. The units will be derived from the equation itself.

Complete step by step solution:First, let us know about the molal elevation constant. It is defined as the elevation in boiling point produced on dissolving the one mole of solute in 1000 g of the solvent.
Now, as mentioned we can derive it in consideration with the molal concentration of solute.
If we talk about the experiment, then it is being shown that for dilute solutions, the elevation of the boiling point is directly proportional to the molal concentration of solute in the solution.
Thus, it can be written as; $\Delta$ T$_b$ ${\displaystyle\propto}$ m; m represent the number of the moles of solute dissolved in a kg of solvent, or we can also say the molality.
Now, $\Delta$ T$_b$ = K$_b$m; here K$_b$ is the molal elevation constant.
Therefore, the units of molal elevation constant is Kkgmol$^{-1}$.
In the last, we can conclude that the molal elevation constant is relatable with the elevation in boiling point, as mentioned. The equation for elevation in boiling point is $\Delta$ T$_b$ = K$_b$m.

Note: Don’t get confused while defining the molal elevation constant. As one more term is there i.e. molal depression constant. There can be confusion in between both the terms. We have already discussed the molal elevation constant, whereas molal depression constant is the freezing point of solution for non-electrolytes.