A gas sample is collected at 21 degrees celsius and 0.988 atm. If the sample has a mass of 4.7 g and a volume of 396 mL. What is the molar mass?

Question

10th grade Chemistry gas law problem. Find the molar mass given the temperature and air pressure.

Answer 1

PV = nRT Ideal Gas Law

P = 0.988 atm

V = 396 ml x 1L/1000 ml = 0.396 L

n = moles of gas = ?

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

T = temperature in K = 21ºC + 273 = 294K

Solve for n:

n = PV/RT = (0.988)(0.396)/(0.0821)(294)

n = 0.0162 moles of gas

Since we know that there are 4.7 g of gas, and we know that molar mass = g/mole, we find the molar mass.

4.7 g/0.0162 moles = 290 g/mole = molar mass