After PbI2 has completely precipitated from an aqueous solution containing Pb2+ and I−, which ions remain dissolved in the solution?

• A. Na+ and NO3−
• B. PbI2 and Na+
• C. Pb2+ and I−
• D. Pb2+ and NO3−

Answer: (A)

Verified step by step guidance

1. Identify the ions present in the original solution before precipitation. Typically, Pb2+ comes from a lead salt and I− comes from an iodide salt, often accompanied by spectator ions such as Na+ and NO3−.
2. Understand that when PbI2 precipitates, it forms a solid by combining Pb2+ and I− ions, removing them from the solution as an insoluble compound.
3. Recognize that ions not involved in the formation of the precipitate remain dissolved in the solution. These are called spectator ions.
4. Since Pb2+ and I− ions form the solid PbI2 and precipitate out, the ions that remain dissolved are the spectator ions, which in this case are Na+ and NO3−.
5. Conclude that after complete precipitation of PbI2, the ions remaining in solution are Na+ and NO3−.