An organic compound contained C 66.7%,H 11.1%,O 22.2% by mass.its relative formula mass was 72.find:

a)the empirical formula of the compound

b)the molecular formula of the compound.

(Ar:H=1,C=12,O=16)

In an experiment to find the number of molecules of water of crystallisationin sodium sulfate crystals,Na₂SO₄.nH₂O,3.22g of sodium sulfate crystals were heated gently .when all the water of crystallisation had been driven off,1.42g of anhdrous sodium sulfate was left.Find the value of n in the formula.(Ar:H=1,O=16,Na=23,S=32)

Gypsum is hydrated calcium sulfate,CaSO₄.nH₂O.A sample of gypsum was heated in a crucible until all the water of crystalissation had been driven off.the following results wewr obtained:

mass of crucible=37.34g

mass of crucible +gypsum,CaSO₄.nH₂O=45.94g

mass of crucible+anhydrous calcium sulfate,CaSO₄=44.14g

calculate the value of n in the formula CaSO₄.nH₂O.

Ar:H=1,O=16,S=32,Ca=40)