Question

1.)

Gas           Number of moles

N2                    3.10

O2                    0.76

CO2                 0.12

If the total pressure is 1.07 atm, what is the partial pressure of Oxygen? (Your answer will be in atmospheres, but do NOT include units - Blackboard won't allow them. Use two decimal places, and simply give the number portion.)

2.) A reaction is carried out that produces hydrogen gas. The gas is collected in an inverted beaker over water at 25 ^oC. The vapor pressure of water at 25 ^oC is 23.78 mmHg. The total pressure in the beaker is determined to be 755.3 torr. What is the partial pressure (in units of torr) of the hydrogen gas in the beaker?

Answer 1

(1) Total number of moles,N = number of moles of N2 + Number of moles of O2 + Number of moles of CO2

                                    = 3.10 + 0.76 +0.12

                                    = 3.98 moles

Mole fraction of Oxygen , X = number of moles of Oxygen / Total number of moles

                                        = 0.76 / 3.98

                                        = 0.191

Partial pressure of Oxygen , p = mole fraction of oxygen x total pressure

                                            = 0.191 x 1.07 atm

                                            = 0.20 atm

Therefore the partial pressure of Oxygen is 0.20 atm

(2) Given total pressure , P = 755.3 torr

Vapour pressure of water , p_H2O = 23.78 mm Hg = 23.78 torr      Since 1 torr = 1 mm Hg

Total pressure , P = vapour pressure of water + Partial pressure of H₂

So Partial pressure of H₂ = P - p_H2O

                                     = 755.3 - 23.78

                                     = 731.5 torr