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

So how much CaCO3 did you have? Won't that be the CaO formed by losing CO2?
How much CO2 did it lose? That will be 8.35 - 6.37 = g CO2

Convert g CO2 to g CaCO3 and from there to percent CaCO3. CaO is the remainder.

Answer 2

dibromine