Question

At a constant temperature, which of the following aqueous solutions will have the maximum vapour pressure?

[Mol weight: $NaCl=58.5,H_2{SO}_4=98.0g.{mol}^{-1}$]

• A. $1$ molal $NaCl$
• B. $1$ molar $NaCl$
• C. $1$ molal $H_2{SO}_4$
• D. $1$ molar $H_2{SO}_4$

Answer 1

The correct option is A $1$ molal $NaCl$

One molar (1M) aqueous solution is more concentrated than one molal aqueous solution of the same solute.

In solution, $H_2{SO}_4$ provides three ions, while $NaCl$ provides two ions. Hence, the vapour pressure of a solution of $NaCl$ is higher (as it gives less number of ions).

Therefore, 1 molal $NaCl$ will have the maximum vapour pressure.

Hence, option $A$ is correct.