, a toxic gas with a rotten egg-like smell, is used for qualitative analysis. If the solubility of i — Solutions and Colligative Properties Chemistry Question
Question
$H_2S$, a toxic gas with a rotten egg-like smell, is used for qualitative analysis. If the solubility of $H_2S$ in water at standard temperature and pressure (STP) is $0.195\text{ M}$, calculate its approximate Henry’s law constant ($K_H$) in atm. (Assume $1\text{ L}$ of water roughly equals $1000\text{ g}$).
Answer: A
💡 Solution & Explanation
A solubility of $0.195\text{ M}$ implies $0.195\text{ moles}$ of $H_2S$ in $1\text{ L}$ of water. Moles of water $n_{H_2O} = \frac{1000}{18} = 55.55\text{ mol}$. Mole fraction $\chi = \frac{0.195}{55.55 + 0.195} \approx 0.0035$. At STP, pressure $P = 1\text{ atm}$. Henry's constant $K_H = \frac{P}{\chi} = \frac{1}{0.0035} \approx 285.7\text{ atm}$. Using exact molecular weights yields $\approx 289.4\text{ atm}$.
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