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

The amount of hydrogen gas collected will be 0.5468 g

Step-by-step 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* 6.50L=n* 62.3637\text{ L.mmHg }mol^(-1)K^(-1)* 309K\\\\n=(810.4* 6.50)/(62.3637* 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* 2g/mol)=0.5468g`

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