Calcium ions treated with aqueous ammonia produce which observation?

• A. White ppt; soluble in excess
• B. No ppt or faint white ppt
• C. Green ppt
• D. White ppt; insoluble in excess

Answer: (B)

Calcium ions with aqueous ammonia show no visible precipitate because ammonia is a weak base and does not supply enough hydroxide ions to force calcium out as calcium hydroxide solid. The amount of OH− produced by typical ammonia solutions is not enough to exceed calcium hydroxide’s solubility product, so calcium ions remain in solution. Additionally, calcium does not form a stable ammine complex that would pull any potential solid into solution. So you observe no precipitate or only a very faint white precipitate under certain concentrations. The other outcomes describe behavior of ions that do form solid hydroxides or interact differently with ammonia (for example, iron giving a colored hydroxide, or a precipitate that can dissolve in excess base), which doesn’t apply to calcium in this test.