Suppose you have a solution that might contain any of the following cations: Ni^(2+), Hg^(+), Fe^(3+) and Ca^(2+). Addition of excess HCl causes a precipitate to form. After the precipitate is filtered off, excess Hsubscript(2)SOsubscript(4) is added to the filtrate and another precipitate forms. This precipitate is filtered off and a solution of NaOH is added to the filtrate until it is strongly alkaline. No precipitate is formed. Which ions are present in each of the precipitates? Which cations are not present in the original solution? Show your reasoning.