Gravimetric analysis is conducted to determine the percentage composition of KCl by precipitating BaSO4 and calculating the mass of Ba(NO3)2 in the original mixture. Spectator ions are Na+ and NO3- and additional information is needed to calculate the mass of BaSO4 precipitate.
To determine the percentage composition of KCl in a mixture, we use gravimetric analysis, where a precipitate is formed and weighed. In the given scenario, BaSO4 is the precipitate formed when a mixture containing KCl and Ba(NO3)2 reacts with Na2SO4. By calculating the molar mass of BaSO4 and the amount in moles precipitated, we can find the mass of Ba(NO3)2 in the original sample. Once the mass of Ba(NO3)2 is known, subtracting this from the total mass of the mixture gives the mass of KCl, which can then be used to calculate its percentage composition.
Regarding the original question, the spectator ions are those ions that do not participate in the formation of the precipitate and remain in solution, in this case, Na+ and NO3-. To calculate the mass of BaSO4 precipitate formed, one would use the stoichiometry of the reaction based on the balanced chemical equation. However, additional data such as the mass of Ba(NO3)2 precipitated or its stoichiometric conversion to BaSO4 would be required to perform this calculation.