A 22.0662 g sample of impure magnesium car- bonate was heated to complete decomposition
according to the equation MgCO3(s) ? MgO(s) + CO2(g) .
After the reaction was complete, the solid residue (consisting of MgO and the original impurities) had a mass of 18.7693 g. Assum- ing that only the magnesium carbonate had decomposed, how much magnesium carbon- ate was present in the original sample?