At a cosntant temperature, which of the following aqueous solutions will have the maximum vapour pressure ?
( Mol. Wt. `Na Cl 58. 5, H _(2) SO _(4) = 98. 0 g mol ^(-1))`

Options

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)`

Answer

A

Explanation

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.