Question

Give a test to distinguish between lead carbonate and zinc carbonate solution?

Answer 1

Add dilute nitric acid separately to both the carbonates. Both dissolve with effervescence due to the evolution of carbon dioxide. Then add potassium iodide (KI) solution to the resulting solutions.

1. Lead carbonate (PbCO₃): A yellow precipitate of lead iodide (PbI₂) is formed.

\[\ce{PbCO3 ​+ 2HNO3​ -> Pb(NO3​)2 ​+ H2​O + CO2​↑}\]

\[\ce{Pb(NO3​)2​ + 2KI -> PbI2​↓ + 2KNO3​}\]

2. Zinc carbonate (ZnCO₃): It dissolves in dilute nitric acid, but on adding KI solution, no yellow precipitate is formed.

\[\ce{ZnCO3​+2HNO3​→Zn(NO3​)2​+H2​O+CO2​↑}\]

The sample that gives a yellow precipitate with KI solution is lead carbonate, while the other is zinc carbonate.