Question

When lead nitrate is heated strongly in a boiling tube, two gases are liberated and a solid residue is left behind in the test tube.

1. Name the type of chemical reaction and define it.
2. Write the name and formula of the coloured gas liberated.
3. Write the balanced chemical equation for the reaction.
4. Name the residue left in the test tube and state the method of testing its nature (acidic/basic).

Answer 1

1. The type of chemical reaction observed when lead nitrate is heated strongly in a boiling tube is a decomposition reaction. A decomposition reaction is a chemical reaction in which a single compound breaks down into two or more simpler products. This process often requires energy, such as heat, to break the chemical bonds in the compound undergoing decomposition.

2. The colored gas liberated during the heating of lead nitrate is nitrogen dioxide (NO₂), which is characterized by its brown fumes​.

3. The balanced chemical equation for the reaction is:
   \[\ce{\underset{(Lead nitrate)}{2Pb(NO3)2(s)}->[Heat]\underset{(Lead oxide)}{2PbO(s)}+\underset{(Nitrogen dioxide)}{4NO2(g)}+\underset{(Oxygen)}{O2}}\]

4. The residue left in the test tube is lead oxide (PbO). The nature of lead oxide can be tested using a litmus test. Since lead oxide is a basic oxide, it will turn red litmus paper blue, indicating its basic nature​.