Question #31fed

1 Answer
Aug 9, 2014

The volume of dry hydrogen would have been 391.6 mL.

This problem involves Dalton's Law of Partial Pressures and Boyle's Law.

See What is Dalton's Law of Partial Pressure? and What is the Boyle's law?.
In your problem,

#P_"t"# = 740.0 Torr

At 18.0 °C, #P_"H₂O"# = 15.5 Torr.

#P_"t" = P_"H₂" + P_"H₂O"#

# P_"H₂" = P_"t" - P_"H₂O"# =(740.0 – 15.5) Torr = 724.5 Torr

Now we use Boyle's Law.

#P_1V_1 = P_2V_2#

#P_1# = 724.5 Torr; #V_1# = 400.0 mL
#P_2# = 740.0 Torr; #V_2# = ?

#V_2 = V_1 × P_1/P_2# = 400.0 mL × #(724.5"Torr")/(740.0"Torr")# = 391.6 mL

This makes sense. We increased the pressure by about 2 %, so the volume should decrease by about 2 % (8 mL).