A mixture contains sand and KClO3. The sand is not affected by heating, while the KClO3 is decomposed to KCl and oxygen by heating. A 5.000 g sample, when heated until no further reaction occurred, gave off a gas which occupied a volume of 0.9605 liters at 24.2 oC and 768.0 torr pressure. What is the percent, by weight, of sand in the mixture?

A chemistry teacher told me this is how to do it:

What is the gas that is given off? Sure, it's oxygen. Use PV=nRT to determine the moles of O2 produced.

Use the equation below to determine the moles of KClO3 that decomposed from the moles of O2 actually produced.

2 KClO3 --> 2 KCl + 3 O2

Find the mass of KClO3 from the moles of KClO3 and subtract from 5.0 grams to get the mass of sand, and its percentage.

But I am still confused. Can someone please help me or break it down into lamen terms for me please!! Thank you!!

The teacher did a very nice job of laying it out for you. Could you be more specific about what you don't understand? Without knowing what you are struggling with, it's difficult to help you without just doing the whole problem for you. We would much prefer to help you find the solution yourself.