Question

A)

A sample of a gas weighs 2.760 g and has a volume of 940 mL at 749 torr and 33°C. What is its molar mass?

___________ g/mol

B)

A sample of argon gas at STP occupies 14.9 L. What mass of argon is present in the container?

_______ g

Answer 1

A)

we have:

P = 749.0 torr

= (749.0/760) atm

= 0.9855 atm

V = 940.0 mL

= (940.0/1000) L

= 0.94 L

T = 33.0 oC

= (33.0+273) K

= 306 K

find number of moles using:

P * V = n*R*T

0.9855 atm * 0.94 L = n * 0.08206 atm.L/mol.K * 306 K

n = 3.687*10^-2 mol

mass(solute)= 2.760 g

we have below equation to be used:

number of mol = mass / molar mass

3.687*10^-2 mol = (2.76 g)/molar mass

molar mass = 74.85 g/mol

Answer: 74.85 g/mol

B)

we have:

P = 1.0 atm

V = 14.9 L

T = 273.0 K

find number of moles using:

P * V = n*R*T

1 atm * 14.9 L = n * 0.08206 atm.L/mol.K * 273 K

n = 0.6648 mol

Molar mass of Ar = 39.95 g/mol

we have below equation to be used:

mass of Ar,

m = number of mol * molar mass

= 0.6648 mol * 39.95 g/mol

= 26.56 g

Answer: 26.56 g