MCQ
Which solution has the highest vapour pressure?
- A$0.02\,\,M\,\,NaCl$ at $50\,^oC$
- B$0.03\,\,M\,\,sucrose$ at $15\,^oC$
- ✓$0.005\,\,M\,\,CaCl_2$ at $50\,^oC$
- D$0.005\,\,M\,\,CaCl_2$ at $25\,^oC$
✓
Answer
Correct option: C.
$0.005\,\,M\,\,CaCl_2$ at $50\,^oC$
c
$\Delta \mathrm{T}_{\mathrm{f}}=\mathrm{i} \times \mathrm{K}_{\mathrm{f}} \times \text { molality }$
$\Delta \mathrm{T}_{\mathrm{f}}=\mathrm{i} \times \mathrm{K}_{\mathrm{f}} \times \text { molality }$
$0.69=i \times 5.12 \times \frac{20 \times 10^{-3} \times 1000}{\frac{94}{1}}$
$i=0.633$
${\mathrm{i}=\left(1-\alpha+\frac{\alpha}{2}\right)} $
${\text { on solving }, \alpha=73.3 \%}$
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