Answer Precipitate begins Ksp Precipitate completes pH≥ pH≥ Ni(OH), 5.0×10-16 6.85 Fe(OH)2.8x1039 2.82 Fe3+:precipitate completes Ni2+:precipitate begins 2.82 6.85 pH c(Fe3+)<10-5 So,the pH can be controlled between 2.82 ~6.852.82 6.85 pH So, the pH can be controlled between 2.82 ~ 6.85 Fe3+: precipitate completes Ni2+: precipitate begins Fe(OH) 2.8 1 0 2.82 39 3 -  Ni(OH) 5.0 1 0 6.85 16 2 -  Answer c(Fe3+)≤10-5 pH pH Precipitate completes Precipitate begins   sp K