If I have an unknown quantity of gas held at a temperature of 1195 K in a steel tank with a volume of 25 liters and a pressure of 560 atm, how many moles of gas do I have?

Question

In the question above, it turns out the gas is Oxygen. How many grams of Oxygen is there

Answer 1

PV = nRT

P = pressure = 560 atm

V = volume = 25 L

n = moles = ?

R = gas constant = 0.0821 Latm/Kmol

T = temperature in K = 1195K

Solve for n:

n = PV/RT = (560 atm)(25 L) / (0.0821 Latm/Kmol)(1195K)

n = 143 mols of gas = 140 mols gas (2 sig. figs.)

If the gas is O₂, the molar mass of O₂ = 32 g/mol

143 mols x 32 g/mol = 4576 g = 4600 g of O₂ (2 sig. figs.)

Answer 2

Here we have an ideal gas law problem, which means we will use the equation P*V = n*R*T. P = 560 atm, V = 25L, T = 1195K and R is a universal constant which you can look up (make sure the units check out! It may help to convert the pressure to pascal) The only value missing is n, the number of moles. So plugging in, we can solve for n. To get mass from moles we need to know the molar mass of oxygen. oxygen gas is O2, which makes the molar mass mO2 = 2 * 15.999 g/mol. So the total mass M = mO2 * n.