Question

A sample of hydrogen gas was collected over water at 36°C and 855 mm Hg. The volume of the container was 6.50 L. Calculate the mass of H2(g) collected. (Vapor pressure of water = 44.6 torr at 36°C)

Answer 1

Answer:

The amount of hydrogen gas collected will be 0.5468 g

Explanation:

We are given:

Vapor pressure of water = 44.6 torr = 44.6 mm Hg

Total vapor pressure = 855 mm Hg

Vapor pressure of hydrogen gas = Total vapor pressure - Vapor pressure of water = (855 - 44.6) mmHg = 810.4 mmHg

To calculate the amount of hydrogen gas collected, we use the equation given by ideal gas which follows:

$PV=nRT$

where,

P = pressure of the gas = 810.4 mmHg

V = Volume of the gas = 6.50 L

T = Temperature of the gas = $36^oC=[36+273]K=309K$

R = Gas constant = $62.3637\text{ L.mmHg }mol^{-1}K^{-1}$

n = number of moles of hydrogen gas = ?

Putting values in above equation, we get:

$810.4mmHg\times 6.50L=n\times 62.3637\text{ L.mmHg }mol^{-1}K^{-1}\times 309K\\\\n=\frac{810.4\times 6.50}{62.3637\times 309}=0.2734\ mol$

To calculate the mass from given number of moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$

Moles of hydrogen gas = 0.2734 moles

Molar mass of hydrogen gas = 2 g/mol

Putting values in above equation, we get:

$0.2734mol=\frac{\text{Mass of hydrogen gas}}{2g/mol}\\\\\text{Mass of hydrogen gas}=(0.2734mol\times 2g/mol)=0.5468g$

Hence, the amount of hydrogen gas collected will be 0.5468 g