Posted by kayla on .
If 267 mL of O2, measured at STP, are obtained by the decomposition of the KClO3 in a 3.33 g mixture of KCl and KClO3, 2KClO3(s) > 2KCl(s) + 3O2
What is the percent by mass of KClO3 in the mixture?

chemistry 
Dr Russ,
Given that 1 mole of any gas occupies 22.4 litres at STP you can calculate the number of moles of O2 in 267 ml, (F moles)
2KClO3(s) > 2KCl(s) + 3O2
tells you that 3 moles of O2 came from 2 moles of KClO3, therefore you can work out how many moles of KClO3 would be needed to yield F moles of O2
number of moles of KClO3
=Fx2/3
Calcluate the molar mass of KClO3, M.
Thus the mass of KClO3 needed is
(Fx2xM/3) g
Hence the percentage of KClO3 in the mixture is
Fx2xMx100%/(3x3.33)