Question

Chemical equilibrium:
The two containers contain liquid X (in A) and Y (in B). X is similar to water and Y is similar to $CC{l}_4$. 20 moles of each are taken in A and B. How many of the following statement(s) is/are correct?
$P_X^0=200torr$
$P_Y^0=50torr$

(i) If $NaCl$ is added to vessel B, the lowering of vapour pressure takes place.
(ii) If glucose is added to vessel A, the boiling point of the solution increases.
(iii) If the valve connecting A and B is opened, then $P_T$ in both the vessel becomes equal and is given by Raoult's law.
(iv) After opening the valve, the level of liquid in both the container decreases (even a slight decrease is to be considered).
(v) After opening the valve, the final pressure in vessel B is more than 50 torr.
(vi) After opening the valve, the final pressure in vessel A is more than 200 torr.

• A. $2$
• B. $3$
• C. $4$
• D. $5$

Answer 1

The correct option is A $2$

i) NaCl is a polar compound. It is insoluble in nonpolar $CC{l}_4$. If NaCl is added to vessel B, the lowering of vapour pressure will not take place.
Thus, statement (i) is incorrect.

ii) When a non-volatile solute is added to the pure solvent, the boiling point of the resulting solution becomes higher than the boiling point of the pure solvent. Hence, if glucose is added to vessel A, the boiling point of the solution increases.
Thus, statement (ii) is correct.

iii) If the valve connecting A and B is opened, then total pressure in both the vessel becomes equal. This is because there is no pressure gradient possible as the vapours in the two compartments can diffuse. But total pressure cannot be given by Raoult's law as the mixture of immiscible liquids are now present in two compartments.
Thus, statement (iii) is incorrect.

iv) The vapour pressure of solution in compartment A is higher than the vapour pressure of solution in compartment B. Hence, after opening the valve, the level of liquid in container A decreases and in the container B increases.
Thus, statement (iv) is incorrect.

v) After some time, appreciable amount of vapours of A will diffuse to vessel B. Hence, after opening the valve, the final pressure in vessel B is more than 50 torr.
Thus, statement (v) is correct.

vi) Vapour pressure of solution is lower than the vapour pressure of pure solvent. The vapour pressure of pure A is 200 torr. After opening the valve, the final pressure in vessel A is less than 200 torr.
Thus, statement (vi) is incorrect.

Thus, out of six statements, only two are correct.