Question

Which one of the following is the ratio of the lowering of vapour pressure of 0.1 M aqueous solutions of $BaC{l}_2,NaCl$ and $A{l}_2(S{O}_4{)}_3$ respectively?

• A. 3 : 2 : 5
• B. 5 : 2 : 3
• C. 5 : 3 : 2
• D. 2 : 3 : 5

Answer 1

Answer: (A)

3 : 2 : 5

Lowering of vapour pressure is a colligative property. It depends on the number of particles of the solute.

$BaC{l}_2\rightleftharpoons B{a}^{2+}+2C{l}^{-};3$ ions

$NaCl\rightleftharpoons N{a}^{+}+C{l}^{-};2$ ions

$A{l}_2(S{O}_4{)}_3\rightleftharpoons 2A{l}^{3+}+3S{O}_4^{3-};5$ ions

Hence, the ratio of lowering of vapour pressure is $3:2:5$ since the concentration of the solutions are same.