Question

1. When gas is collected over water, the gas is saturated with water vapor with its partial pressure of water vapor dependent on temperature. In the textbook, there is a given saturated water vapor at various temperatures. Use that table to solve the following problem:

During the decomposition of KClO₃, 92.0mL of gas is collected by the displacement of water at 25.0C. If the atmospheric pressure is 756mmHg, what mass of O₂ is collected?

2. (a) if you have a sample of gas, when the temperature increases and assume the volume of gas remain constant, discuss how the pressure will change using the arguments in kinetic theory of gas.

(b) In a similar way, discuss how the pressure will change if you have high number of moles of gas in the same container of gas.

3. If an unknown gas molecule is subjected to effuse through a porous barrier in 1.50 min; under the same condition of temperature and pressure, it takes 4.73 min of nitrogen gas (N₂) (with the same volume as unknown gas) to effuse through the barrier. Predict the molar mass of the unknown gas.

Please answer all questions, Thank you in advance!

Answer 1

Q.1: Vapor pressure of water at 25 ^oC = 23.8 mm Hg

Hence pressure due to pure O₂, P = 756mmHg - 23.8 mm Hg = 732.2 mmHg = 0.96342 atm

V = 92 mL * (1 L / 1000 mL) = 0.092 L

T = 25+273.15 = 298.15 K

Applying ideal gas equation:

PV = nRT

=> n = PV / RT = 0.96342 atm * 0.092 L / (0.08206 L.atm.mol^-1K^-1 * 298.15 K) = 0.003623 mol O2

=> mass of O2 formed = 0.003623 mol O2 * (32.0 g / 1 mol) = 0.116 g (Answer)

Q.2: (a): When we increase temperature, the gaseous molecules receive heat and move with higher speed. High speed particles exerts higher pressure on wall of the container. Hence pressure increases.

(b): When we increases the number of gas molecules, the number of gas molecules colloiding per unit area of of the container also increases. Hence pressure also increases.