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Chemistry · 2024 · 5 marks
CBSE 2024 · Region 1 · Set 1 · Q31
(a) (i) At the same temperature, CO_2 gas is more soluble in water than O_2 gas. Which one of them will have higher value of K_H and why? (ii) How…
(i)
At the same temperature, $\displaystyle \mathrm{CO}_{2}$ gas is more soluble in water than $\displaystyle \mathrm{O}_{2}$ gas. Which one of them will have higher value of $\displaystyle \mathrm{K}_{\mathrm{H}}$ and why ?
(ii)
How does the size of blood cells change when placed in an aqueous solution containing more than $\displaystyle 0 \cdot 9 \%$ (mass/volume) sodium chloride ?
(iii)
$\displaystyle 1$ molal aqueous solution of an electrolyte $\displaystyle \mathrm{A}_{2} \mathrm{~B}_{3}$ is $\displaystyle 60$% ionized. Calculate the boiling point of the solution. (Given : $\displaystyle \mathrm{K}_{\mathrm{b}}$ for $\displaystyle \mathrm{H}_{2} \mathrm{O}=0.52 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$ )
(i)
The vapour pressures of A and B at $\displaystyle 25$°C are $\displaystyle 75$ mm Hg and $\displaystyle 25$ mm Hg , respectively. If A and B are mixed such that the mole fraction of A in the mixture is $\displaystyle 0 \cdot 4$, then calculate the mole fraction of B in vapour phase.
(ii)
Define colligative property. Which colligative property is preferred for the molar mass determination of macromolecules ?
(iii)
Why are equimolar solutions of sodium chloride and glucose not isotonic?
Marking-scheme solution
(a) (i)As \(\displaystyle \mathrm{K}_{\mathrm{H}} \propto \frac{1}{\text { Solubility }}\) of Gas
\(\displaystyle \therefore \mathrm{O}_{2}\) gas has higher \(\displaystyle \mathrm{K}_{\mathrm{H}}\); because higher the \(\displaystyle \mathrm{K}_{\mathrm{H}}\) value, lower the solubility of gas in liquid.
(ii) Blood cells shrink.
(iii) \(\displaystyle \Delta \mathrm{T}_{\mathrm{b}}=\mathrm{iK}_{\mathrm{b}} \mathrm{m}\)
\(\displaystyle \mathrm{T}_{\mathrm{b}}-\mathrm{T}_{\mathrm{b}}{ }^{0}=\mathrm{i} \times 0.52 \mathrm{~K} \mathrm{Kg} \mathrm{mol}^{-1} \times 1 \mathrm{~mol} \mathrm{Kg}^{-1}\)
\[\alpha=\frac{\mathrm{i}-1}{\mathrm{n}-1}
\]
\[\mathrm{n}=5
\]
\[0 \cdot 6=\frac{\mathrm{i}-1}{5-1}
\]
\[\mathrm{i}=3 \cdot 4
\]
\[\mathrm{T}_{\mathrm{b}}-373 \mathrm{K}=3.4 \times 0.52 \times 1
\]
\[\mathrm{T}_{\mathrm{b}}=1.768+373 \mathrm{~K}
\] \(\displaystyle \mathrm{T}_{\mathrm{b}}=374.768 \mathrm{~K}\) (If boiling point of water is 373.15K then \(\displaystyle \mathrm{T}_{\mathrm{b}}=374.918 \mathrm{~K}\) )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.