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,

$\frac{P_1V_1}{T_1}=\frac{P_2V_2}{T_2}$

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:

$\frac{751torr\times 40.0mL}{293K}=\frac{760torr\times V_2}{273K}$

$V_2=36.8mL$

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