Question

A 0.642g sample of an unknown gas was collected over water at 25.0°C and 1.04 atm. The collection cylinder contained 151.3 mL of gas after the sample was released. Find the molar mass of the unknown gas.

Answer 1

Molar Mass = 99.7669.

To solve, first use the equation PV=nRT and solve for n, the number of moles. You do this by finding that n=PV/RT. Then plug in your values above, make sure your temperature is in kelvins by adding 273 and your volume is in liters (151.3 mL = 0.1513 L). You get that n=.006435. You can then solve for the molar mass by dividing your given mass, 0.642g, by the number of moles you solved for, .006435, and get 99.7669 g/mol

Answer 2

Answer : The molar mass of unknown gas is 99.8 g/mole.

Explanation :

Using ideal gas equation:

`PV=nRT\\\\PV=(w)/(M)RT`

where,

P = pressure of gas = 1.04 atm

V = volume of gas =
`151.3ml=0.1513L`

conversion used :
`(1L=1000ml)`

T = temperature of gas =
`25.0^oC=273+25.0=298K`

R = gas constant = 0.0821 L.atm/mole.K

w = mass of an unknown gas = 0.642 g

M = molar mass of an unknown gas = ?

Now put all the given values in the ideal gas equation, we get:

`(1.04atm)* (0.1513L)=(0.642g)/(M)* (0.0821L.atm/mole.K)* (298K)`

`M=99.8g/mole`

Therefore, the molar mass of unknown gas is 99.8 g/mole.