1)
Mr(CaSO3) = Mr = Ar(Ca) + Ar(S) + 3Ar(O) = 40 + 32 + 3 * 16 = 120
w(Ca) = Ar(Ca) / Mr = 40 / 120 = 0.33 = 33%
w(S) = Ar(S) / Mr = 32 / 120 = 0.27 = 27%
w(O) = 3Ar(O) / Mr = 48 / 120 = 0.4 = 40%
2)
Mr(CuO) = Mr = Ar(Cu) + Ar(O) = 64 + 16 = 80
w(Cu) = Ar(Cu) / Mr = 64 / 80 = 0.8 = 80%
w(O) = Ar(O) / Mr = 16 / 80 = 0.2 = 20%
3)
Mr(H2SO4) = Mr = 2Ar(H) + Ar(S) + 4Ar(O) = 2 * 1 + 32 + 4 * 16 = 98
w(H) = 2Ar(H) / Mr = 2 / 98 = 0.02 = 2%
w(S) = Ar(S) / Mr = 32 / 98 = 0.33 = 33%
w(O) = 4Ar(O) / Mr = 64 / 98 = 0.65 = 65%
