Calculate the mass of O2 produced by the decomposition of KClO3 when 856 mL of O2 is collected over water at 20.0°C and 1.015 atm. (The vapor pressure of water at 20.0°C is 17.5 torr.)

1.1296 grams of O2 is produced.  

Explanation:

n = number of mole

R = 0.082057

V = 0.856 L

Therefore,

n = 0.0353 mole

g = 0.0353 mole x 32.0 g/mole = 1.1296 g of O2

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)

може ли да зареждате повече информация, моля