Question

2 g of lead nitrate powder is taken in a boiling tube. The boiling tube is heated over a flame. Now answer the following :(a) state the color of the fumes evolved and the residue left. (b) Name the type of chemical reactions that has taken place stating its balanced chemical equation.

CBSE Class X Science SA 2 (3 Marks)

Answer 1

2 Pb (NO3)2 (s) ===> heat  ==>  2 PbO (s)  + 4 NO2 (g)+  O2 (g)

The color of NO2 fumes is reddish brown.

Answer 2

State of the color of the fumes evolved and the residue left:

The colorless lead (II) nitrate crystals upon heating undergoes thermal decomposition and forms a yellow solid precipitate of lead oxide and evolves "reddish brown fumes" of nitrogen dioxide gas.  

Chemical reactions:

Upon heating lead nitrate strongly, it decomposes with a crackling sound and a precipitate of lead oxide is formed along with the release of oxygen and nitrogen dioxide gas.

The oxygen liberated can be tested by introducing a glowing splint near the boiling tube. The nitrogen dioxide gas produced is acidic and turns blue litmus paper red.

Balanced equation:  $2 P b\left(N O_{3}\right)_{2} \rightarrow 2 \mathrm{PbO}(\mathrm{s})+\mathrm{NO}_{2}+\mathrm{O}_{2}$