Question

Solid potassium chlorate (KClO3) was placed in an evacuated closed 1.00 L flask which was then heated to 400°C to completely decompose the KClO3 to form solid potassium chloride and oxygen gas. The resulting pressure of the oxygen gas in the flask at 400°C was determined to be 1.35 atm. How many grams of the KClO3 was initially placed in the flask ?

(1) 1.0g (2) 2.0g (3) 3.0g (4) 4.0g (5) 5.0g

The answer is 2.0 g but I'm not sure why.

Answer #1

A sample of soilid potassium chlorate was heated and decomposed
into solid potassium chloride and oxygen gas. The oxygen produced
was collected over water at 22 degrees celcius at a total pressure
of 745 Torr. the volume of the gas collected was 0.650 L, and the
vapor pressure of water at 22 degrees celcius is 21 torr.
2 KClO3(s)=2KCl(s)+3O2(g)
First calculate the partial pressre of oxygen in the gas
collected and determine the mass of potassium chlorate in the
sample...

Potassium chlorate (KClO3 molar mass 122.5 g/mol) decomposes
into oxygen gas and potassium chloride. When 3.25 grams of
potassium chlorate decomposes at 610 torr and 34*C, what is the
volume of oxygen gas produced? Remember to convert torr to atm and
Celcius to Kelvin. 2 KClO3 --> 3 O2(g) + 2 KCl (s).

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