Oxygen gas can be prepared in a Laboratory by the reaction:
2KClO3(s) => 2KCl(s) + 3O2(g)
How many grams of KClO3 must be reacted to produce100g of O2?
To do this question, all you're really concerned with is the Oxygen. Remember that everything you start with, you'll end up with in the reaction. You want 100g of O2 so ...
This solution uses the molecular weights of K, Cl and O to determine how many moles of KClO3 will be needed to get 100g of O2. 150 worlds.