Question

A one molal solution of sodium chloride in water has the same boiling point as

• A. $1m$ solution of magnesium sulphate
• B. $1m$ solution of magnesium chloride
• C. $1m$ solution of aluminium sulphate
• D. $1m$ solution of aluminium chloride.

Answer 1

Answer: (A)

$\Delta T_b=i{K}_{b}m$
Two solutions having same molality and same van't Hoff factors will have same elevation in boiling points $\left(\Delta T_b,\right)$ and thus, have same boiling points $\left(T_b,\right)$
For $NaCl,i=2;MgS{O}_4,i=2;MgC{l}_2,i=3;A{l}_2{\left(S{O}_4\right)}_3,i=5$ and $AlC{l}_3,i=4$.
Thus; one molal solution of sodium chloride in water has the same boiling point as one molal solution of $MgS{O}_4$