When 12.2 g of benzoic acid is dissolved in 100g of water,

Question:

When $12.2 \mathrm{~g}$ of benzoic acid is dissolved in $100 \mathrm{~g}$ of water, the freezing point of solution was found to be $-0.93^{\circ} \mathrm{C}\left(\mathrm{K}_{f}\left(\mathrm{H}_{2} \mathrm{O}\right)=1.86 \mathrm{~K} \mathrm{~kg}\right.$ $\mathrm{mol}^{-1}$ ). The number $(\mathrm{n})$ of benzoic acid molecules associated (assuming $100 \%$ association) is_____.

Solution:

$\Delta \mathrm{T}_{\mathrm{f}}=\mathrm{i} \times \mathrm{k}_{\mathrm{f}} \times \mathrm{m}$

$0-(-0.93)=\mathrm{i} \times 1.86 \times \frac{12.2}{122 \times 100} \times 1000$

$\mathrm{i}=\frac{0.93}{1.86}=0.5$

$\mathrm{i}=1+\left(\frac{1}{\mathrm{n}}-1\right) \alpha$

$\frac{1}{2}=1+\left(\frac{1}{n}-1\right) \times 1$

$\mathrm{n}=2$

Leave a comment

Close

Click here to get exam-ready with eSaral

For making your preparation journey smoother of JEE, NEET and Class 8 to 10, grab our app now.

Download Now