Given the following, what is the pressure of dry hydrogen gas if the vapor pressure of water at 25°C is 3.8 mm Hg?

Hydrogen gas produced in the laboratory by the reaction of zinc and hydrochloric acid as collected over water at 25°C. The barometric pressure at the time was 742.5 mm Hg.

1 Answer
Nov 6, 2016

Answer:

#P_"Total"=P_"Gas"+P_"SVP"="742 mm Hg"#

Explanation:

And #P_"SVP"# is the so called #"saturated vapour pressure"#, which for this experiment #=# #"3.8 mm Hg"#

So #P_"dihydrogen"# #=# #"742 mm Hg "-" 3.8 mm Hg = 738.2 mm Hg"#.

Note that here the quoted value of #P_"SVP"# is wrong. I suspect that they got confused with respect to a pressure measurement in #"mm Hg"# and #"Pascal"#.

The vapour pressure of water at #298*K# is #"24 mm Hg"#.