Asolution contains 0.036 m cu2+ and 0.044 m fe2+. a solution containing sulfide ions is added to selectively precipitate one of the metal ions from solution. at what concentration of sulfide ion will a precipitate begin to form? what is the identity of the precipitate? ksp(cus) = 1.3 × 10-36, ksp(fes) = 6.3 × 10-18.