A 130.-mL sample of gas is collected over water at 22°C and 753 torr. What is the volume of the dry gas at STP? (The vapor pressure of water at 22°C is 20. torr.)

Question

Quizplus · Accepted Answer

First, correct the total pressure to find the pressure of the dry gas by subtracting the water vapor pressure from the total pressure: 753 torr - 20 torr = 733 torr. Then, use the combined gas law, $P_1V_1/T_1 = P_2V_2/T_2$, converting temperatures to Kelvin (295K for 22°C and 273K for 0°C, STP) and pressures to the same units (torr). Solving for $V_2$ gives a volume that does not match any of the provided options exactly, indicating that the correct answer is "none of these."

A 130-ML Sample of Gas Is Collected Over Water at 22°C