I am trying to complete this chemistry class and need some help with
some of my problems.  The question is listed below, any help you can
give me is greatly appreciated and can you direct me to a website
where I can get some additional help with Freshman Chemistry.

"Pure oxygen gas can be prepared in the laboratory by the
decomposition of solid potassium chlorate to form solid potassium
chloride and oxygen gas.  How much oxygen gas in grams can be prepared
from 45.8 g of potassium chlorate?"

Thank you.

First you need to write a balanced chemical equation:
2KClO3 ----- 2KCl + 3 O2
Now if you have 45.8g of KClO3.. How many moles of KClO3 do you have?
The molar mass of KClO3 is 122.55 g/mol.
Therefore there are 45.8g/122.55g = 0.37372501 moles.
Now use molar ratios to find the moles of O2:
0.373 mol/2 = xmols / 3
x mols = 0.560587515 moles of O2.
Now to find the mass of the O2 produced use the molar mass of oxygen
to multiply it by the number of moles:
0.560587515 mol x 15.9994 g/mol = 8.97 g of O2 are produced.
Notice there are 3 significant digits in the question, so the final
answer also has 3 significant digits.


Hopefully that helps!!

Brian