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Ch.5 - Gases
Chapter 5, Problem 103

When hydrochloric acid is poured over potassium sulfide, 42.9 mL of hydrogen sulfide gas is produced at a pressure of 752 torr and 25.8 °C. Write an equation for the gas-evolution reaction. Determine how much potassium sulfide (in grams) reacted.

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1
Write the balanced chemical equation for the reaction: \( \text{K}_2\text{S} + 2\text{HCl} \rightarrow 2\text{KCl} + \text{H}_2\text{S} \).
Convert the volume of hydrogen sulfide gas from mL to L: \( 42.9 \text{ mL} = 0.0429 \text{ L} \).
Use the ideal gas law \( PV = nRT \) to find the number of moles of \( \text{H}_2\text{S} \). Convert the pressure from torr to atm: \( 752 \text{ torr} \times \frac{1 \text{ atm}}{760 \text{ torr}} \).
Convert the temperature from Celsius to Kelvin: \( 25.8^\circ\text{C} + 273.15 \). Use \( R = 0.0821 \text{ L atm mol}^{-1} \text{ K}^{-1} \).
Calculate the moles of \( \text{K}_2\text{S} \) using the stoichiometry from the balanced equation, then convert moles of \( \text{K}_2\text{S} \) to grams using its molar mass.