Question

If 2.50L of hydrogen gas is collected over water at 35.0C and 750 mm Hg, what is the volume of dry gas at standard conditions? The vapor pressure of water is 42.2 mm Hg at 35.0C. I know the answer is 2.06 L, but am not sure how to do the equation

Answer 1

Answer – Given, volume of H₂ V1 = 2.50 L , T1 = 35+273 = 308 K ,

P od water at 35^oC = 42.2 mm Hg

So, pressure of H₂ at 35^oC = 750 mm Hg – 42.2 mm Hg = 707.8 mmHg

At standard condition, T2 = 273 K , P = 760 mm Hg

We know combine gas law

P1V1/T1 = P2V2/T2

So, V2 = P1V1T2/ P2T1

           = 707.8 mm Hg * 2.50 L * 273 K / 760 mm Hg * 308 K

           = 2.06 L

So the volume of dry gas at standard conditions is 2.06 L