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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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.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Gas-Evolution Reactions

Gas-evolution reactions occur when a chemical reaction produces a gas as one of its products. In this case, hydrochloric acid reacts with potassium sulfide to produce hydrogen sulfide gas. Understanding the reactants and products involved is crucial for writing the balanced chemical equation that represents the reaction.

Ideal Gas Law

The Ideal Gas Law (PV = nRT) relates the pressure, volume, temperature, and number of moles of a gas. This law is essential for calculating the amount of potassium sulfide that reacted, as it allows us to determine the number of moles of hydrogen sulfide produced from the given volume and conditions of the gas.

Stoichiometry

Stoichiometry involves the calculation of reactants and products in chemical reactions based on balanced equations. By using the balanced equation for the gas-evolution reaction, we can relate the moles of hydrogen sulfide produced to the moles of potassium sulfide that reacted, allowing us to calculate the mass of potassium sulfide consumed in the reaction.

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