Question

The boiling point of $0.2\mathrm{mol}{\mathrm{kg}}^{-1}$ solution of $\mathrm{x}$in water is greater than equimolal solution of $\mathrm{y}$in water. Which of the following statement is true in this case?

• A. molecular mass of $\mathrm{x}$ is less than the molecular mass of $\mathrm{y}$
• B. $\mathrm{y}$ is undergoing dissociation in water while $\mathrm{x}$ undergoes no change
• C. $\mathrm{x}$ is undergoing dissociation in water
• D. molecular mass of $\mathrm{x}$ is greater than the molecular mass of $\mathrm{y}$

Answer 1

The correct option is C

$\mathrm{x}$ is undergoing dissociation in water

Explanation for the correct option:

Option(C): $\mathrm{x}$ is undergoing dissociation in water

• Given that the boiling point of $0.2\mathrm{mol}{\mathrm{kg}}^{-1}$ the solution of $\mathrm{x}$in water is greater than the equimolar solution of $\mathrm{y}$in water, which can be shown as:

${\left({\mathrm{\Delta T}}_{\mathrm{b}}\right)}_{\mathrm{x}}>{\left({\mathrm{\Delta T}}_{\mathrm{b}}\right)}_{\mathrm{y}}$

• As the solution has the same solvent so, ${\mathrm{K}}_{\mathrm{b}}$ (Boiling point constant)is the same.
• Also as the solution has an equimolar mixture, the value $\mathrm{m}$ is also constant.
• Hence it can be shown as :

$$\begin{gathered} {\mathrm{i}}_{\mathrm{x}}.{\mathrm{k}}_{\mathrm{b}}.\mathrm{m}>{\mathrm{i}}_{\mathrm{y}}.{\mathrm{k}}_{\mathrm{b}}.\mathrm{m} \\ \Rightarrow {\mathrm{i}}_{\mathrm{X}}>{\mathrm{i}}_{\mathrm{y}} \end{gathered}$$

• Here the $"\mathrm{i}"$ denotes the dissociation constant, so it can be concluded that, $\mathrm{x}$ is undergoing dissociation in water.

Explanation for the incorrect option:

Option(A): molecular mass of $\mathrm{x}$ is less than the molecular mass of $\mathrm{y}$

• The solution of $\mathrm{x}$ have a molecular mass, that is given to be similar to that of the molecular mass of $\mathrm{y}$.
• Thus, the given option does not represent the correct concept.

Option(B):$\mathrm{y}$ is undergoing dissociation in the water while undergoing no change

• Here is the given case, which is undergoing dissociation in water.
• Hence, the given option is the incorrect one.

Option(D): molecular mass of $\mathrm{x}$ is greater than the molecular mass of $\mathrm{y}$

• The solution of $\mathrm{x}$ have a molecular mass, that is given to be similar to that of the molecular mass of $\mathrm{y}$.
• Thus, the given option does not coincide with the correct concept.

Hence, the statement which is true in the given case is that: $\mathrm{x}$ is undergoing dissociation in water.