Asample of hydrogen gas was collected over water at 21°c and at a pressure equal to the atmospheric pressure of 748 mm hg. the volume of the sample was 512 ml. how many grams of h2 are in the sample? the vapor pressure of water at 21°c is 18.7 mmhg.

The amount of hydrogen gas in the sample is 0.0408 g

Explanation:

We are given:

Vapor pressure of water = 18.7 mmHg

Total vapor pressure = 748 mmHg

Vapor pressure of hydrogen gas = Total vapor pressure - Vapor pressure of water = (748 - 18.7) mmHg = 729.3 mmHg

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

where,

P = pressure of the gas = 729.3 mmHg  

V = Volume of the gas = 512 mL = 0.512 L ( 1 mL = 0.001 L)

T = Temperature of the gas =

R = Gas constant =

n = number of moles of hydrogen gas = ?

Putting values in above equation, we get:

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

Moles of hydrogen gas = 0.0204 moles

Molar mass of hydrogen gas = 2 g/mol

Putting values in above equation, we get:

Hence, the amount of hydrogen gas in the sample is 0.0408 g