Question

If 0.896 g of a gas occupies a 250 mL flask at 20°C and 760 mm Hg of pressure, what is the molar mass of the gas?​

Answer 1

Answer:

86.2 g/mol

Explanation:

Before you can find the molar mass, you first need to calculate the number of moles of the gas. To find this value, you need to use the Ideal Gas Law:

PV = nRT

In this equation,

-----> P = pressure (mmHg)

-----> V = volume (L)

-----> n = moles

-----> R = Ideal Gas constant (62.36 L*mmHg/mol*K)

-----> T = temperature (K)

After you convert the volume from mL to L and the temperature from Celsius to Kelvin, you can use the equation to find the moles.

P = 760 mmHg                                      R = 62.36 L*mmHg/mol*K

V = 250 mL / 1,000 = 0.250 L              T = 20 °C + 273.15 = 293.15 K

n = ? moles

PV = nRT

(760 mmHg)(0.250 L) = n(62.36 L*mmHg/mol*K)(293.15 K)

190 = n(18280.834)

0.0104 = n

The molar mass represents the mass (g) of the gas per every 1 mole. Since you have been given a mass and mole value, you can set up a proportion to determine the molar mass.

$\frac{?grams}{1 mole} =\frac{0.896grams}{0.0104moles}$                                      <----- Proportion

$?grams(0.0104moles) = 0.896$                       <----- Cross-multiply

$?grams = 86.2$                                               <----- Divide both sides by 0.0104