Qualitative Analysis: Test For Cations! Trivia Quiz

Explanation
When Sodium Hydroxide is added to a solution containing Fe2+, it forms a dirty green precipitate. This precipitate does not redissolve when excess Sodium Hydroxide is added. Therefore, the correct answer is Fe2+.

Explanation
When sodium hydroxide is added to a solution containing Fe 3+, it forms a reddish-brown precipitate. This precipitate does not redissolve when excess sodium hydroxide is added. This is due to the formation of a complex compound called iron(III) hydroxide, which is insoluble in water. The reddish-brown color of the precipitate is characteristic of Fe 3+ ions. Therefore, the presence of a reddish-brown precipitate that does not redissolve confirms the presence of Fe 3+ ions in the solution.

Explanation
Cu2+ forms a blue precipitate when Sodium Hydroxide is added. This indicates the presence of Cu2+ ions in the solution. The blue precipitate does not redissolve in the excess reagent, suggesting that it is insoluble. Therefore, Cu2+ is the correct answer.

Explanation
Cu2+ ions form a blue precipitate when aqueous ammonia is added. This precipitate can then redissolve in the excess ammonia to form a dark blue solution. Therefore, the correct answer is Cu2+.

Explanation
When aqueous ammonia is added to Fe2+, it forms a dirty green precipitate. This precipitate does not redissolve in the excess reagent. Based on this information, the correct answer is Fe2+.

Explanation
When aqueous ammonia is added to a solution containing Fe3+, it forms a reddish-brown precipitate. This precipitate does not redissolve even when excess ammonia is added. This indicates the presence of Fe3+ in the solution.

Explanation
When aqueous ammonia is added to a solution containing Ca2+ and NH4+, no precipitate forms. This is because Ca2+ and NH4+ ions do not react with ammonia to form an insoluble compound. In other words, the combination of Ca2+ and NH4+ ions with ammonia does not result in the formation of a solid that would precipitate out of the solution. Therefore, the correct answer is Ca2+, NH4+, NH4+, Ca2+.

Explanation
When aqueous ammonia is added to a solution containing Zn 2+, a white precipitate is formed. This white precipitate is the result of the reaction between Zn 2+ and the hydroxide ions (OH-) from the ammonia. However, the precipitate redissolves when excess ammonia is added because it forms a complex ion with Zn 2+, which is soluble in excess ammonia. Therefore, the presence of a white precipitate that redissolves in excess reagent confirms the presence of Zn 2+ in the solution.

Explanation
When aqueous ammonia is added to a solution containing Pb2+, Mg2+, and Al3+, a white precipitate is formed. This precipitate does not redissolve in the excess reagent, indicating that it is insoluble. Therefore, the correct answer is Pb2+, Mg2+, Al3+.

Explanation
When Sodium Hydroxide is added to a solution containing Mg2+ and Ca2+, a white precipitate is formed. This precipitate does not redissolve in the excess reagent. Therefore, the correct answer is Mg2+, Ca2+, Ca2+, Mg2+.

Explanation
When sodium hydroxide is added to a solution containing Pb2+, Zn2+, and Al3+, it forms a white precipitate. However, this precipitate redissolves in the excess reagent. Therefore, the correct answer is Pb2+, Zn2+, Al3+.