# Chemistry

posted by Smushy

A 7.65 g sample of potassium chlorate,KClO3, was heated to decompose all the oxygen. It was found that 2.25 L of oxygen was collected over water at 25.00degreesC and 1.00 atm of pressure. The vapor pressure of water at that temperature is 23.8 mm Hg. How many moles of oxygen were collected?

So far I know the temperature is 298 Kelvin, the volume is 2.25 L, thewater has apressure of 1 atm and the Vapor has a pressure of mm Hg, but I don't know where to start. how do I solve this question.

1. DrBob222

Use PV = nRT
Ptotal = 760 mm
pH2O = 23.8
ptotal = pH2O + pO2. Solve for pO2 then pO2 in atm = pO2 in mm Hg/760 = ?
V you know
R you know (0.08206 L*atm/mol*K)
T = 298
Solve for n = number mols O2 at these conditions.
You don't need the 7.65g KClO3 since the problem gave you L O2.

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