Mass relationships grade 11 chemistry

Hello, I can't seem to understand how mass relationships in Stiochiometry works. For this part of my homework, I can't do the simplest question. Please help me with the following questions ( I am grateful for help).

What mass of oxygen will be produced by heating 400 g of potassium chlorate?

2KClO3 -> 2KCl + 3O2

Also, How many grams of anhydrous cupric sulphate (CUSO4) can be made from 100 grams of bluestone (CuSO4 * 5H2O)?

Thanks in advance for any help.

First change 400g of KClO3 to moles
400g/122.5g=3.27moles of KClO3
Now the moles of KClO3 in the balanced equation is 2 moles to 3 moles of O2
3.27moles KClO3x 3moles O2/2moles of KClO3= 4.9moles of O2. The question calls for grams of O2, so 4.9moles O2 x 32g/1moleO2=156.7gO2

CuSO4*5H2O has a mass of 250grams
CuSO4 has a mass of 160g
This means there is 36% water in the hydrate
Therefore if you have 100g of the hydrate there can be 64g after the water is out.

hmmmm......ur 1st question: two moles of kclo3 will give 3 moles of o2.....okkk..so 1 mole of kclo3 will give 1.5 moles of o2....... Since 400 gm of kclo3 =400/122.5 moles......
As the mm of kclo3 is 122.5
so. O2 produced=1.5*400/122.5.......which is the required answer......2nd questioon is similar....

Mm... It may help. http://giftchoice.info/454587/sulfate