Number of moles of lab gas from the ideal gas law?

Question

0.014 mass of lab gas; 21 degress celcius room temp; 294K (kelvins); 120.999 (flask, gas & stoppper weight); Pressure=761.8 mm Hg; L ATM= 760mm Hg; R(gas law constant) = 0.0821

ideal gas law formula is PV=nRT

If you have any ways to figure this out, please help and even if you can set up the problem, please do so. I can do rest of the work. This assignment is due tomorrow. PLZ help! Thx!

Answer 1

n = PV/RT

T = given

R = given

P = given

V = unknown,  

You need either the volume of the flask or the molecular weight of the gas to solve the problem.