A 142-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 = 20.torr)
A)122 mL
B)162 mL
C)136 mL
D)111 mL
E)none of these

Question

Quizplus · Accepted Answer

To find the volume of the dry gas at STP, we first need to correct the total pressure to account for the vapor pressure of water. The total pressure is 753 torr, and the vapor pressure of water at 22°C is 20 torr. Therefore, the pressure of the dry gas is 753 torr - 20 torr = 733 torr. We can then use the combined gas law to find the volume of the gas at STP (0°C and 760 torr). The combined gas law formula is (P1 * V1) / T1 = (P2 * V2) / T2, where P is pressure, V is volume, and T is temperature in Kelvin. Converting 22°C to Kelvin gives 295K, and STP temperature (0°C) is 273K. Rearranging the formula to solve for V2 gives V2 = (P1 * V1 * T2) / (P2 * T1). Substituting the values gives V2 = (733 torr * 142 mL * 273K) / (760 torr * 295K). This calculation does not directly match any of the provided options, indicating that the correct answer is not explicitly listed among the options provided.

A 142-ML Sample of Gas Is Collected Over Water at 22°C