Question

Calcium metal and water produce hydrogen gas. If the vol-

ume of wet gas collected over water is 95.0 mL at 20 °C and
758 mm Hg, what is the volume of dry gas at STP condi-
tions? (The vapor pressure of water at 20 °C is 17.5 mm Hg.)

Answer 1

The volume of dry gas at STP conditions is 82.98 mL.

Step-by-step explanation:

To calculate the volume of dry gas at STP conditions, we need to consider the vapor pressure of water. The given volume of wet gas collected over water is 95.0 mL at 20 °C and 758 mm Hg. The vapor pressure of water at 20 °C is 17.5 mm Hg. To find the volume of dry gas, we use the equation:

P1V1/T1 = P2V2/T2

Where P1 is the initial pressure, V1 is the initial volume, T1 is the initial temperature, P2 is the final pressure, V2 is the final volume, and T2 is the final temperature.

Solving for V2, we can substitute P1 as 758 mm Hg, V1 as 95.0 mL, T1 as 20°C + 273 = 293 K, P2 as atmospheric pressure at STP = 760 mm Hg, and T2 as 273 K:

V2 = (P1 * V1 * T2) / (P2 * T1)

Plugging in the values, we get:

V2 = (758 mm Hg * 95.0 mL * 273 K) / (760 mm Hg * 293 K) = 82.98 mL (rounded to two decimal places).