A gas in a container has a pressure of 0.77 atm, volume of 65,5 L and a temperature of 235 K. If the gas is helium, what mass of helium is in the container?
A) 2.61 g
B) 10.5 g
C) 0.625 g
D) 0.859 g

B) 10.5

Explanation:

PV= NRT     -> N=PV/RT

N= mols .     P= pressure . V= volume in Liters    T= temp in Kelvin (Celsius degree = 273.15) .  R= Gas constant (.0821 for atm)

N=(.77 x 65.5)/(.0821x235) = 2.614 mols of Helium

Mols x Molecular weight = weight in grams

2.614x4.003(Molecular weight ot He) = 10.46 round to 10.5