the total pressure in the system is 3.00 atm
the mixture contains only oxygen and helium. Pressure of gases in a mixture is additive. pressure exerted by individual gases are called partial pressures.
the addition of all the partial pressures of the gases making up the mixture is the total pressure of the system.
partial pressure of oxygen + partial pressure of helium = total pressure
partial pressure of oxygen = 0.200 atm
0.200 atm + partial pressure of helium = 3.00 atm
partial pressure of helium = 2.80 atm
pressure exerted by helium gas alone is 2.80 atm
we can use the ideal gas law equation to find the number of moles of helium in the mixture
PV = nRT
where P - 2.80 atm
V - volume - 10.0 L
n - number of moles
R - universal gas constant - 0.0821 L.atm/mol.K
T - temperature in kelvin - 273 + 20 °C = 293 K
substituting the values in the equation
2.80 atm x 10.0 L = n x 0.0821 L.atm/mol.K x 293 K
n = 1.16 mol
mass of He = number of moles x molar mass
mass = 1.16 mol x 4.00 g/mol = 4.64 g
mass of He present = 4.64 g
