chem help please molar mass?

Question

a 10.0 l vessel is filled with nitrogen gas at 1.00 atm and 300K. When 7.94g. of another gas is added to the vessel at 300K, the toatl pressure rises to 1.350 atm. What is the molar mass of the added gas. Can u solve with work its really hard.

Answer 1

Increase in pressure is .35

Moles of N2 = 10/(0.0812*300) = 0.411 mol

Thus moles now, .411*1.35 = .555 mol

So, moles of gas = 0.144

Thus molar mass of gas = 7.94/.144 = 55.14 g