Question

A sample of 40.0 mL of hydrogen is collected by water displacement at a temperature of 20 degrees Celcius. The barometer reads 751 torr. What is the volume of the hydrogen at STP (standard temperature and pressure)?

Answer 1

Answer : The volume of the hydrogen at STP is, 36.8 mL

Explanation :

Combined gas law is the combination of Boyle's law, Charles's law and Gay-Lussac's law.

The combined gas equation is,

`(P_1V_1)/(T_1)=(P_2V_2)/(T_2)`

where,

`P_1` = initial pressure of gas = 751 torr

`P_2` = final pressure of gas at STP = 760 torr

`V_1` = initial volume of gas = 40.0 mL

`V_2` = final volume of gas at STP = ?

`T_1` = initial temperature of gas =
`20^oC=273+20=293K`

`T_2` = final temperature of gas at STP =
`0^oC=273+0=273K`

Now put all the given values in the above equation, we get:

`(751torr* 40.0mL)/(293K)=(760torr* V_2)/(273K)`

`V_2=36.8mL`

Therefore, the volume of the hydrogen at STP is, 36.8 mL