Question

A gas is collected over water at 20C in a eudiometer tube until the pressure is equilibrated with the atmospherica pressure. What is the preussre of the dry gas if the barometric pressure is 771?

Answer 1

Let's assume that the pressure given is 771 torr.

Answer:

747.44 torr

Explanation:

The eudiometer tube is a setup that collects gas in a liquid (generally water). After the thermal equilibrium, the gas becomes in equilibrium with the vapor of water above the liquid.

By Dalton's law, the total pressure of a mixture is the sum of the partial pressure of its components. The partial pressure is the pressure that the gas would have at the same conditions if it was alone. So, the pressure of the dry gas is its partial pressure.

The total pressure is the barometric pressure, and the partial pressure of the water vapor at 20°C is 23.56 torr (the value can be found at a thermodynamic table). So, the pressure of the dry gas (P) is:

771 = 23.56 + P

P = 771 - 23.56

P = 747.44 torr