Question

A small gas cylinder containing CH4 (methane) gas is found to have a mass of 246.776g, and is used to bubble methane into a container that has been submerged in 22.0 C water. The volume of the gas that is inside the container at the end is 0.228L, and the gas cylinder weighs 246.622g. The barometric pressure of the room is 1.05atm.

1. Calculate the mass of CH4 that was released into the container.

2. Calculate the temperature of the water (and thus CH4 gas) in Kelvins.

3. Find the vapor pressure of water at this temperature.

4. Determine the partial pressure being exerted by the CH4 in the container in atm.

5. Use the ideal gas law and your calculated data above to calculate the number of moes of CH4 that were in the container.

6. Use the data from parts 1. and 5. to calculate the experimental molar mass of CH4

Answer 1

(1)

Mass of gas released into the container = Change in mass of container = 246.776-246.622 = 0.154 g

(2)

Temp of water and gas = 22⁰C = 273+22 = 295 K

(3)

Using the chart we see that vapor pressure of water at this temp = 19.8 torr = 0.026 atm

(4)

Pressure exerted by water + Pressure exerted by methane = 1.05 atm

So,

Pressure exerted by methane = 1.05-0.026 = 1.024 atm

(5)

Using ideal gas equation:

PV = nRT

Putting values:

1.024*0.228 = n*0.0821*295

Solving we get:

n = 0.00964 moles

(6)

Experimental molar mass = Mass/moles = 0.154/0.00964 = 15.975 g