A mixture of calcium oxide, CaO, and calcium carbonate, CaCO3 that had a mass of

Question

A mixture of calcium oxide, CaO, and calcium carbonate, CaCO3 that had a mass of 1.844 g was heated until all the calcium carbonate was decomposed according to the following equation. After heating, the sample had a mass of 1.462 g. Calculate the mass of CaO and CaCO3 present in the original sample.

Explanation / Answer

CaCO3 --- >CaO + CO2 let initial mass of CaO be x, so mass of CaCO3 is 1.844-x mol. wt of CaCO3 = 100 gm/mol mol wt of CaO = 40+16 = 56 gm/mol moles of CaCO3 originally present = (1.844-x)/100 moles of CaO originally present : x/56 moles of CaCO3 lost = (1.844-x)/100 as 1 mol CaCO3 gives 1 mol CaO (1.844-x)/100 mol of CaO will be produced after decomposition of CaCO3 as CO2 is volatile, it is lost finally 1.462gm is left and CaCO3 is completely decomposed so final moles of CaO is 1.462/56 = 0.02611 total moles of CaO = moles of CaO initially present + moles of CaO produced by decomposition so put all values (1.462/56) = (x/56) + (1.844-x)/100 or, (1.462-x)/(1.844-x) = (56/100) solve to get x = 0.976gm hence initial mass of CaO = x = 0.976gm CaCO3 = (1.844-x) = 0.868gm

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