Dolomite is a mixed carbonate of calcium and magnesium. Calcium and magnesium carbonates both decompose on heating to produce the metal oxides, MgO and CaO, and CO2. If 4.84g of residue consisting of MgO and CaO remains when 9.66g of dolomite is heated until decomposition is complete, what percentage by mass of the original sample was MgCO3?
let x mass MgCO3 (molar mass 83.3 g/mol) let y mass CaCO3 ( molar mass 100.1 g/mol) x + y 9.66 mass CO2 evolved 9.66 - 4.84 4.82 g moles CO2 4.82 g / 44 g/mol0.110 the ratio between MgCO3 and CO2 is 1 : 1; the ratio between CaCO3 and CO2 is 1 : 1 x / 83.3 + y /100.1 0.110 100.1 x + 83.3 y 917.2 x 9.66-y 100.1 ( 9.66-y) + 83.3 y 917.2 967 - 100.1 y + 83.3 y 917.2 - 16.8 y - 49.8 y 2.96 g mass MgCO3 9.66 - 2.966.70 g % MgCO3 6.70 x 100/ 9.66 69.4
