Q. At a constant temperature, which of the following aqueous solutions will have the maximum vapour pressure? (Mol. wt NaCl =58.5, $H_{2}SO_{4}\ = 98.0\ g.mol^{- 1}$)
A) 1 molal NaCl (aq)
B) 1 molar NaCl (aq)
C) 1 molal $H_{2}SO_{4}\ (aq)$
D) 1 molar $H_{2}SO_{4}\ (aq)$
Explanation
(a)
One molar (1 M) 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, vapour pressure of solution of NaCl is higher (as it gives less ions). Therefore, 1 molal NaCl will have the maximum vapour pressure.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.