Question

A solution contains some or all of the ions Cu2+, Al3+, K+, Ca2+, Ba2+, Pb2+, and NH4+. The following tests were performed, in order, on the solution.

Addition of 6 M HCl produced no reaction.
Addition of H2S with 0.2 M HCl produced a black solid.
Addition of (NH4)2S produced a white solid.
Addition of (NH4)2HPO4 in NH3 produced no reaction.
The final supernatant when heated produced a purple flame.
Identify which of these ions were present in the solution, which were absent, and for which ones no conclusions can be drawn.

Answer 1

Tests on a solution revealed the likely presence of Cu2+ or Pb2+ due to a black solid from H2S, the presence of Al3+ due to a white solid from (NH4)2S, and the presence of K+ due to a purple flame. The absence of reactions with HCl and (NH4)2HPO4 leaves other ions' statuses inconclusive.

Step-by-step explanation:

The analysis of the given solution through sequential chemical tests can identify the presence, absence, or indeterminate status of specific ions in the solution. The addition of 6 M HCl with no reaction suggests that ions that form insoluble chlorides are absent. When H2S in 0.2 M HCl produced a black solid, this indicates the presence of either Cu2+ as copper sulfide or Pb2+ as lead sulfide since both are black in color. The addition of (NH4)2S produced a white solid, which could indicate the presence of Al3+ as aluminum hydroxide. The absence of a reaction with (NH4)2HPO4 in NH3 means it is inconclusive for phosphate-forming ions. Finally, a purple flame upon heating the supernatant strongly suggests the presence of K+, as this is a characteristic flame color for potassium.