Question

When 0.873 g of neon is added to an 700-cm3 bulb containing a sample of argon, the total pressure of the gases is found to be 1.73atm at a temperature of 298 K .
Find the mass of the argon in the bulb.

Answer 1

Calculation of pressure exerted by Neon :

We know that PV = nRT

Where

T = Temperature = 298 K

P = pressure = ?(= atm)

n = No . of moles = mass/molar mass

                          = 0.873 g / 20 (g/mol)

                          = 0.04365 mol

R = gas constant = 0.0821 L atm / mol - K

V= Volume of the gas = 700 cm3 = 700x0.001 L      Since 1 cm3 = 0.001 L

                               = 0.7 L

Plug the values we get P = (nRT) / V

                                     = 1.52 atm

So the pressure exerted by argon is = total pressure - pressure of Ne gas

                                                     = 1.73 - 1.52

                                                     = 0.21 atm

Calculation of number of moles of Ar :

We know that PV = nRT

Where

T = Temperature = 298 K

P = pressure = 0.21 atm

n = No . of moles = ?

R = gas constant = 0.0821 L atm / mol - K

V= Volume of the gas = 0.7L

Plug the values we get n = (PV) / (RT)

                                      = 0.006 moles

Mass of Ar is , m = number of moles x molar mass

                          = 0.006 mol x 40 (g/mol)

                         = 0.24 g

Therefore the mass of Ar present is 0.24 g