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Chemistry · 2024 · 5 marks
CBSE 2024 · Region 4 · Set 2 · Q31
(a) (i) Define reverse osmosis. (ii) Why are aquatic species more comfortable in cold water in comparison to warm water? (iii) A solution containing…
(i)
Define reverse osmosis.
(ii)
Why are aquatic species more comfortable in cold water in comparison to warm water ?
(iii)
A solution containing $\displaystyle 2$ g of glucose $\displaystyle \left(\mathrm{M}=180 \mathrm{~g} \mathrm{~mol}^{-1}\right)$ in $\displaystyle 100$ g of water is prepared at $\displaystyle 303$ K. If the vapour pressure of pure water at $\displaystyle 303$ K is $\displaystyle 32.8$ mm Hg , what would be the vapour pressure of the solution ? $\displaystyle 1+1+3$
(i)
Predict whether Van't Hoff factor will be less or greater than one, when Ethanoic acid is dissolved in benzene.
(ii)
Define ideal solution.
(iii)
Calculate the mass of $\displaystyle \mathrm{CaCl}_{2}$ (molar mass $\displaystyle =111 \mathrm{~g} \mathrm{~mol}^{-1}$ ) to be dissolved in $\displaystyle 500$ g of water to lower its freezing point by 2K, assuming that $\displaystyle \mathrm{CaCl}_{2}$ undergoes complete dissociation. $\displaystyle 1+1+3$ $\displaystyle \left(\mathrm{K}_{\mathrm{f}}\right.$ for water $\displaystyle \left.=1.86 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\right)$
Marking-scheme solution
(a) (i) If a pressure larger than the osmotic pressure is applied to the solution side, resulting in the movement of solvent particles from solution to solvent.
(ii) Solubility of gases in water decreases with rise in temperature. More oxygen will be available in the cold water.
\[\begin{aligned}
& \frac{p_{1}^{0}-p_{1}}{p_{1}^{0}}=\frac{n_{2}}{n_{1}} \\
& \frac{p_{1}^{0}-p_{1}}{p_{1}^{0}}=\frac{\mathrm{w}_{2} \times \mathrm{M}_{1}}{\mathrm{M}_{2} \times \mathrm{w}_{1}}
\end{aligned}
\]
\(\displaystyle \frac{32.8-p_{1}}{32.8}=\frac{2 \times 18}{180 \times 100}\)
\(\displaystyle 32.8-p_{1}=0.0656\)
\(\displaystyle p_{1}=32.734 \mathrm{~mm} \mathrm{Hg}\)More from Solutions
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CBSE Class 12 Chemistry past-paper question from the 2024 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.