CBSE 2024 · Region 1 · Set 1 · Q31 · 5 marks
(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?
(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 \(\displaystyle \mathrm{T}_{\mathrm{b}}=374.918 \mathrm{~K}\) )SolutionsVapour Pressure of Liquid SolutionsApplylong_answermedium
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CBSE Class 12 Chemistry past-paper question from the 2024board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.