Gravimetric analysis does not always involve a precipitate. Consider the following problem. A mixture of calcium carbonate and calium oxide has a mass of 8.35 grams. When heated strongly, the CaCO3 in the sample decomposes into solid CaO and carbon dioxide gas. The calcium oxide in the original sample is not altered by heating. After heating, the mass of the sample is 6.37 grams. Using the information given, calculate the % by mass of calcium oxide in the original sample.

Answer 1

Write the equation for CaCO3 and balance it.
CaO in the sample is just an innocent bystander. Loss in weight on heating is due to CaCO3. How much did it lose? 8.35-6.37 = mass CO2.
Convert mass CO2 to mass CaCO3.
Then %CaCO3 = (mass CaCO3/mass sample)*100 = ??

%CaO = 100%-%CaCO3