Calculate the mass fraction of each element in marble , whose composition corresponds to the formula CaCO3.

given:
CaCO3
find:
ω(Ca) - ?
ω(C) -?
ω(O) -?
Solution:
Мr(CaCO3) = Аr(Ca) + Аr(C) + 3Аr(O) = 40 + 12 + 3 • 16 = 100
ω(Ca)=Аr(Ca)/Мr(CaCO₃) •100 %= 40/100•100 %  = 40 %
ω(C)=Аr(C)/Мr(CaCO₃)   •100 % = 12/100•100 %= 12%
ω(O)=3Аr(O)/Мr(CaCO₃) •100 %  = 48/100•100 %= 48 %
Answer :ω(Ca) = 40 %; ω(C) = 12 %; ω(O) = 48 %.