CBSE 2025 · Region 2 · Set 3 · Q22 · 3 marks
Henry's law constant for $\displaystyle \mathrm{CO}_{2}$ in water is $\displaystyle 1.67 \times 10^{8} \mathrm{~Pa}$ at $\displaystyle 298$ K. Calculate the number of moles of $\displaystyle \mathrm{CO}_{2}$ in $\displaystyle 540$ g of soda water when packed under $\displaystyle 3.34 \times 10^{5} \mathrm{~Pa}$ at the same temperature.
Marking-scheme solution
$$x_{\mathrm{CO_2}} = \frac{P_{\mathrm{CO_2}}}{K_{\mathrm{H}}}
= \frac{3.34 \times 10^{5}}{1.67 \times 10^{8}}
= 2 \times 10^{-3}
2 \times 10^{-3} = \frac{n_{\mathrm{CO_2}}}{n_{\mathrm{CO_2}} + n_{\mathrm{H_2O}}}
For a dilute solution,
2 \times 10^{-3} = \frac{n_{\mathrm{CO_2}}}{n_{\mathrm{H_2O}}}
n_{\mathrm{CO_2}} = \frac{540}{18} \times 2 \times 10^{-3}
= 6 \times 10^{-2}\ \text{mol.}$$
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CBSE Class 12 Chemistry past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.