Question

A student collected a sample of hydrogen gas by displacement of water. The volume of the sample is 90.0 mL. The temperature is 25°C and the atmospheric pressure is 745 mm. The equilibrium vapor pressure of water at 25°C is 23.8 mm Hg. Calculate the number of moles of hydrogen gas collected.

Answer 1

To calculate the number of moles of hydrogen gas collected, we can use the ideal gas law equation. In this case, the pressure is the atmospheric pressure minus the vapor pressure of water. Substituting the values into the equation, we find that the number of moles of hydrogen gas collected is approximately 0.039 moles.

Step-by-step explanation:

To calculate the number of moles of hydrogen gas collected, we can use the ideal gas law equation: PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the gas constant, and T is the temperature in Kelvin.

In this case, the pressure is the atmospheric pressure minus the vapor pressure of water. The temperature needs to be converted to Kelvin by adding 273.15. The gas constant is 0.0821 L·atm/mol·K.

Substituting the values into the equation, we have (745 mm - 23.8 mm) × (90.0 mL / 1000 mL/L) = n × (0.0821 L·atm/mol·K) × (25°C + 273.15).

Simplifying and solving for n, we find that the number of moles of hydrogen gas collected is approximately 0.039 moles.