(a) What is observed when aqueous solutions of potassium iodide and lead nitrate are mixed together? Name the type of reaction and write the chemical equation for the reaction that occurs.

OR

(b) When copper powder is heated in a watch glass, a black substance is formed.

(i) Why is this black substance formed? Name it.

(ii) How can this black substance be reversed to its original form?

(a) When aqueous solutions of potassium iodide and lead nitrate are mixed together, a yellow precipitate of lead iodide is formed. This is an example of a double displacement reaction. The chemical equation for the reaction is:

$$2KI(aq) + Pb(NO_3)_2(aq) ightarrow 2KNO_3(aq) + PbI_2(s)$$

OR

(b) (i) The black substance formed is copper oxide. It is formed due to the oxidation of copper powder when heated in air.

(ii) The black substance (copper oxide) can be reversed to its original form (copper) by heating it in a reducing flame.