Question

A 500 mL gas sample is collected over water at a pressure of 740mmHg and 25 degrees C. What is the volume of the dry gas at STP?

Answer 1

The volume of the dry gas at STP is = 0.4314 L

Step-by-step explanation:

We are given:

Total vapor pressure = 740 mmHg

Also, considering Vapor pressure of water = 23.78 mmHg

Vapor pressure of gas = Total vapor pressure - Vapor pressure of water = (740 - 23.78) mmHg = 716.22 mmHg

We use the equation given by ideal gas which follows:

`PV=nRT`

where,

P = pressure of the gas = 716.22 mmHg

V = Volume of the gas = 500 mL = 0.5 L ( 1 ml = 0.001 L )

T = Temperature of the gas =
`25^oC=[25+273]K=298K`

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

n = number of moles of gas = ?

Putting values in above equation, we get:

`716.22mmHg* 0.5L=n* 62.3637\text{ L.mmHg }mol^(-1)K^(-1)* 298K\\\\n=(716.22* 0.5)/(62.3637* 298)=0.01926mol`

At STP, 1 mole of gas yields a volume of 22.4 L

So,

0.01926 mole of gas yields volume of
`0.01926* 22.4\ L`

Hence, the volume of the dry gas at STP is = 0.4314 L