Question

Which of the following aqueous solutions should have the highest boiling point?
(i) 1.0 M NaOH
(ii) 1.0 M Na2SO4
(iii) 1.0 M NH4NO3
(iv) 1.0 M KNO3


NCERT Class XII
Chemistry - Exemplar Problems

Chapter 2. Solutions

Answer 1

Option (ii) 1.0 M Na2SO4 is correct because its molecular mass is highest among all that's why its boiling point will be highest among four.

Answer 2

$\bold{1.0 \mathrm{M}\ \mathrm{Na}_{2} \mathrm{SO}_{4}}$ solution should have the highest boiling point.  So, the correct option is (ii).

The elevation in boiling point is a colligative property. A colligative property depends on the number of particles present in solute present in the given solution.  

Hence we can say that more number of ions will increase the boiling point of solution.  

Ere in the given options, $\bold{\mathrm{Na}_{2} \mathrm{SO}_{4}}$ will form three ions:

$\mathrm{Na}_{2} \mathrm{SO}_{4} \rightarrow 2 \mathrm{Na}^{+}+\mathrm{SO}_{4}^{-2}$

Whereas all other molecules will form 2 ions such as:

$\mathrm{NaOH} \rightarrow \mathrm{Na}^{+}+\mathrm{OH}^{-}$

$\mathrm{KNO}_{3} \rightarrow \mathrm{K}^{+}+\mathrm{NO}_{3}^{-}$

$\mathrm{NH}_{4} \mathrm{NO}_{3} \rightarrow \mathrm{NH}_{4}^{+}+\mathrm{NO}_{3}^{-}$

Hence $\mathrm{Na}_{2} \mathrm{SO}_{4}$ will have highest boiling point.