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Determine the mass of CaCO3?
A sample contains only CaCO3 and KCl. CaCO3 decomposes upon heating according to the equation below. Determine the mass of CaCO3 in a 3.456 g sample that when heated decomposed to leave a residue with a mass of 2.845 g.
CaCO3 (s) when heated it produces CaO (s) + CO2
Please show calculations and explain
1 Answer
- Anonymous9 years agoFavourite answer
I'll try to explain this as fully as I can - bear with me ;)
OK, so if the residue has a lower mass than the original sample, the mass loss can only be caused by escaping CO2 - it's no longer locked up as CaCO3 and so it escapes.
The mass of CaCO2 is 3.456 - 2.845 = 0.611g.
Now, you need to find how many moles of CO2 are present.
No. of moles = Mass in grams / molecular mass of compound
Molecular mass of CO2 is 12 + (16*2) = 44
Moles = 0.611/44 = 0.0139 moles of CO2
CaCO3 = CaO + CO2
In the above equation, for every one molecule of CaCO3 that there was, there is only one molecule of CO2 produced. Therefore, there are exactly the same number of moles of CaCO3, i.e. 0.0139 moles.
Now, to calculate the mass of CaCO3 you use this equation:
Mass in grams = number of moles * molecular mass of compound
Molecular mass of CaCO3 = 40 + 12 + (16*3) = 100
Mass of CaCO3 is 100 * 0.0139 moles = 1.39 grams CaCO3 in the sample.
If you don't understand something, say so and I'll edit my answer to explain.