Question

A sample of a gas weighs 1.25g at 28 C° occupying volume of 2.50×10² ml and pressure is 715 torr. What is molar mass in grams?

Answer 1

Answer: Molar mass of the gas is 131.3 g

Explanation :

The given problem can be solved using Ideal Gas Equation.

The equation can be written as,

$PV = nRT$

We have been given P = 715 torr.

Let us convert this to atm unit. The conversion factor is 1 atm = 760 torr.

$715 torr \times \frac{1 atm}{760torr}= 0.941atm$

T = 28 C = 28 +273 = 301 K

V = 2.50 x 10² mL. Let us convert this to L.

$2.50 \times 10^{2}mL \times \frac{1 L}{1000mL}= 0.250 L$

R = 0.0821 L-atm/mol K

Let us rearrange the given equation to solve for n.

$n = \frac{PV}{RT}$

Let us plug in the above values.

$n = \frac{0.941 atm \times 0.250 L}{0.0821 L-atm/mol K \times 301 K}$

$n = \frac{0.23525}{24.7121}$

n = 0.00952 mol

The molar mass of a gas is calculated as,

$M = \frac{Grams}{mol}$

$M = \frac{1.25 grams}{0.00952 mol}$

M = 131.3 g/mol

Molar mass of the gas is 131.3 g