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Which Ions Remain in Solution After PBI2 Precipitation Is Complete?
When a solid substance dissolves in a solvent, it dissociates into ions, which are charged particles. However, in some cases, when two ions combine, they can form a solid precipitate, which is insoluble and settles at the bottom of the container. One such example is the precipitation of lead(II) iodide (PbI2).
PbI2 is a yellow solid that can be formed by mixing lead(II) nitrate (Pb(NO3)2) and potassium iodide (KI) solutions. The reaction between these two solutions produces lead(II) iodide, which is insoluble in water and forms a precipitate. The chemical equation for this reaction is as follows:
Pb(NO3)2 (aq) + 2KI (aq) → PbI2 (s) + 2KNO3 (aq)
During the precipitation of PbI2, some ions remain in the solution while others form the solid precipitate. The ions that remain in solution after the precipitation is complete include potassium ions (K+) and nitrate ions (NO3-). These ions are from the potassium iodide and lead nitrate solutions used to form PbI2. Since both potassium ions and nitrate ions are highly soluble in water, they do not combine to form a precipitate and remain dispersed in the solution.
The lead(II) ions (Pb2+) from the lead nitrate solution combine with the iodide ions (I-) from the potassium iodide solution to form the insoluble lead(II) iodide precipitate. This precipitate settles at the bottom of the container and can be separated from the solution by filtration or decantation.
It is important to note that the solubility of lead(II) iodide is very low in water, which is why it forms a precipitate. However, if other ions are present in the solution that can form complex compounds with lead(II) ions, the solubility of PbI2 can be increased. For example, the addition of excess iodide ions can lead to the formation of soluble complex compounds like PbI4^2- or PbI3^-. These complexes prevent the complete precipitation of lead(II) iodide.
FAQs:
Q: Why does lead(II) iodide form a precipitate?
A: Lead(II) iodide forms a precipitate because it is insoluble in water. When lead(II) nitrate and potassium iodide solutions are mixed, the lead(II) ions combine with the iodide ions to form the insoluble precipitate.
Q: What happens to the potassium and nitrate ions during the precipitation?
A: The potassium and nitrate ions remain in solution after the precipitation is complete. They do not combine to form a precipitate as they are highly soluble in water.
Q: Can lead(II) iodide be dissolved in water?
A: Lead(II) iodide has a very low solubility in water. It forms a precipitate when mixed with lead(II) nitrate and potassium iodide solutions. However, the addition of excess iodide ions can lead to the formation of soluble complex compounds, increasing the solubility of PbI2.
Q: How can the lead(II) iodide precipitate be separated from the solution?
A: The lead(II) iodide precipitate can be separated from the solution by filtration or decantation. Filtration involves passing the mixture through a filter paper, which retains the solid precipitate and allows the liquid to pass through. Decantation involves carefully pouring off the liquid while leaving the solid precipitate at the bottom.
Q: Are there any other factors that can affect the solubility of PbI2?
A: Yes, the solubility of lead(II) iodide can be influenced by factors such as temperature and the presence of other ions that can form complex compounds with lead(II) ions. These factors can increase or decrease the solubility of PbI2 in water.
In conclusion, during the precipitation of lead(II) iodide (PbI2), the potassium and nitrate ions remain in solution, while the lead(II) ions combine with the iodide ions to form the insoluble precipitate. Understanding the ions that remain in solution after precipitation is essential in various fields, including analytical chemistry and environmental science.
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