My question concerns the ideal gas law.

Question

A 2.000-L tank is found containing gas at 27.0 degrees C and 23.11 atm.

a. Determine the number of moles of gas in the tank.

b. If the mass of the gas is found to be 133.0 g, confirm which halogen is in the tank.

Answer 1

Ideal Gas Law:

PV = nRT

P = pressure = 23.11 atm

V = volume in liters = 2.000 L

n = moles = ?

R = gas constant = 0.0821 Latm/Kmol

T = temperature in Kelvin = 27.0ºC + 273.15 = 300.15K

Solving for moles (n) ..

n = PV/RT = (23.11)(2.000) / (0.0821)(300.15)

n = 1.8756 moles = 1.88 moles (3 sig.figs.)

From the given mass (133.0 g) we can determine the molar mass as follows:

molar mass = g / mol = 133.0 g / 1.88 mols = 70.7 g / mole

Since the halogens (F, Cl, Br, I) occur as diatomic molecules (F₂, Cl₂, Br₂ and I₂), this most closely corresponds to Cl₂ gas with a molar mass of 70.9 g / mole