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.
To calculate the percentage by mass of calcium oxide (CaO) in the original sample, we need to determine the mass of calcium oxide formed during the decomposition of calcium carbonate (CaCO3).
1. Start with the mass of the original sample:
- Initial mass = 8.35 grams
2. After heating, the total mass of the sample decreased:
- Final mass = 6.37 grams
The mass difference (initial mass - final mass) represents the mass of carbon dioxide gas that escaped during heating.
- Mass of CO2 = Initial mass - Final mass
3. The remaining mass is attributed to the calcium oxide:
- Mass of CaO = Final mass
4. Now we can calculate the percentage of calcium oxide in the original sample using the following formula:
- % by mass of CaO = (Mass of CaO / Initial mass) * 100
Substituting the values:
- % by mass of CaO = (Final mass / Initial mass) * 100
Thus, the equation becomes:
- % by mass of CaO = (6.37 grams / 8.35 grams) * 100
Calculating this expression will give us the percentage by mass of calcium oxide in the original sample.