Question

Which of the following aqueous solutions has the highest increase in boiling point?

• A. $0.0001\mathrm{M}\mathrm{NaCl}$
• B. $0.0001\mathrm{M}\mathrm{Urea}$
• C. $0.01\mathrm{M}\mathrm{NaCl}$
• D. $0.001\mathrm{M}{\mathrm{MgCl}}_2$

Answer 1

The correct option is C

$0.01\mathrm{M}\mathrm{NaCl}$

Explanation for the correct option:

(c ) $0.01\mathrm{M}\mathrm{NaCl}$

• $\mathrm{\Delta T}=\mathrm{i}\times {\mathrm{k}}_{\mathrm{b}}\times \mathrm{m}$
• $0.01\mathrm{M}\mathrm{NaCl},\mathrm{i}\times \mathrm{m}=2\times 0.01=0.02\mathrm{M}$
• $\mathrm{i}\times \mathrm{m}\mathrm{of}(0.001\mathrm{M})$$\mathrm{NaCl}$ is highest, hence its boiling point will also increase the maximum.
• Hence this option is correct

Explanation for the incorrect options:

(b)$0.0001\mathrm{M}\mathrm{Urea}$

• $0.0001\mathrm{M}\mathrm{urea},\mathrm{i}\times \mathrm{m}=1\times 0.0001=0.0001\mathrm{M}$
• i=1 for urea as it is non-electrolyte.
• $\mathrm{i}\times \mathrm{m}\mathrm{of}(0.001\mathrm{M})$$\mathrm{NaCl}$ is highest, hence its boiling point will also increase the maximum.
• Thus, this option is incorrect.

(d) $0.001\mathrm{M}{\mathrm{MgCl}}_2$

• $0.001\mathrm{M}{\mathrm{MgCl}}_2,\mathrm{i}\times \mathrm{m}=3\times 0.001=0.003\mathrm{M}$
• $\mathrm{i}\times \mathrm{m}\mathrm{of}(0.001\mathrm{M})$$\mathrm{NaCl}$ is highest, hence its boiling point will also increase the maximum.
• Thus, this option is incorrect.

Hence the correct option is (c ) $0.01\mathrm{M}\mathrm{NaCl}$