This question concerns the stoichiometry of gases.

Question

Scientists are studying the effect of a synthetic atmosphere on plant growth. The components of the synthetic atmosphere are 80.5 mol percent Ar, 18.0 mol percent O2, and 1.5 mol percent C02.

a. If the total pressure of the gas mixture is to be 748 Torr, determine the partial pressure for the argon in this mixture.

b. If this atmosphere is to be contained in a vessel with a volume of 165 L at a pressure of 295 K, how any moles of Ar are needed.

Answer 1

Refer to / review Dalton's Law of Partial Pressure

a). P_Ar = 748 torr x 80.5% = 602 torr (3 sig.figs.)

b). Did you mean at a TEMPERATURE of 295K or did you mean at a PRESSURE of 295 Torr?

With a temperature of 295K, and we want to find moles, we can use the ideal gas law:

PV = nRT

P = Pressure of Ar = 602 torr x 1 atm / 760 torr = 0.792 atm of Ar

V = Volume in liters = 165 L

n = moles of Ar = ?

R = gas constant = 0.0821 Latm/Kmol

T = temperature in Kelvin = 295K

Solving for n (moles of Ar):

n = PV/RT = (0.792)(165) / (0.0821)(295)

n = 5.40 moles of Ar (3 sig.figs.)