Question

What is the molar mass of an unknown gas if the density of that gas is 0.726 grams/liter at a pressure of 0.634 atm and a temperature of 25oC?

a. 2.35 g/mole
b. 28.0 g/mole
c. 53.2 g/mole
d. 64.0 g/mole

Answer 1

b. 28.0 g/mole

Step-by-step explanation:

Given:

d = 0.726 g/L

P = 0.634 atm

T = 25°C + 273 = 298 K

We can use the ideal gas equation of state:

PV= nRT

Since d=mass/V = nM/V, we can modify the equation to obtain the molar mass of the gas (M):

PM = dRT

⇒ M = dRT/P = (0.726 g/L x 0.082 L.atm/K.mol x 298 K)/(0.634 atm)= 27.87 g/mol ≅ 28 g/mol

Therefore, the correct option is b. 28.0 g/mole