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.

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.

dibromine

To calculate the % by mass of calcium oxide in the original sample, we need to determine the mass of calcium oxide in the sample before and after heating.

1. Determine the mass of calcium oxide before heating:
- Subtract the mass of the sample after heating from the mass of the sample before heating.
- Mass of calcium oxide before heating = Mass of sample before heating - Mass of sample after heating
- Mass of calcium oxide before heating = 8.35 grams - 6.37 grams

2. Calculate the % by mass of calcium oxide in the original sample:
- Divide the mass of calcium oxide before heating by the mass of the sample before heating.
- % by mass of calcium oxide = (Mass of calcium oxide before heating / Mass of sample before heating) x 100

Now let's calculate:

1. Mass of calcium oxide before heating:
Mass of calcium oxide before heating = 8.35 grams - 6.37 grams
Mass of calcium oxide before heating = 1.98 grams

2. % by mass of calcium oxide in the original sample:
% by mass of calcium oxide = (Mass of calcium oxide before heating / Mass of sample before heating) x 100
% by mass of calcium oxide = (1.98 grams / 8.35 grams) x 100

Calculating the value:
% by mass of calcium oxide = 0.237 x 100
% by mass of calcium oxide = 23.7%

Therefore, the % by mass of calcium oxide in the original sample is 23.7%.