A 500.-L sample of oxygen gas at 24 °C was
prepared by decomposing a 3.0% aqueous
solution of hydrogen peroxide, H²O² in the
presence of a small amount of manganese
catalyst by the reaction
2H²0²(aq) › 2H²0(g) + 0²(g)

The oxygen thus prepared was collected by
displacement of water. The total pressure
collected was 755 mm Hg. What is the partial
pressure of oxygen in the mixture? How many moles of oxygen are in the mixture? (The vapor pressure of water at 24°C is 23 mm Hg.)