Question

State one chemical test between each of the following pairs:
Ferrous nitrate & Lead nitrate.

Answer 1

Hint: A chemical reaction in which the 2 reactants react to give an insoluble salt is called precipitation. The cations and anions combine to form a precipitate. The precipitation reactions are single replacement reactions or double replacement reactions. Here, in ferrous nitrate and lead nitrate, there are different cations present whereas the anions are the same. Precipitation reactions are useful in determining whether a particular element is present in a solution or not.

Complete step by step answer:
We will discuss the chemical test one by one.
Ferrous nitrate
\[Fe(NO{}_3){}_2 + 2NaOH \to Fe(OH){}_2 + 2NaNO{}_3\]
Ferrous nitrate is reacted with sodium hydroxide and produces ferrous hydroxide and sodium nitrate. By this reaction, the precipitation of ferrous hydroxide is occurring as the result of dirty green precipitates.
Lead nitrate
\[Pb(NO{}_3){}_2 + 2NaOH \to Pb(OH){}_2 + 2NaNO{}_3\]
In this reaction, lead nitrate is also reacted with sodium hydroxide and gives the lead hydroxide and sodium nitrate as products. A chalky white color precipitate indicates the presence of lead hydroxide.
These reactions are the double displacement reactions, which give the solid precipitates that are insoluble.
Therefore, from the above explanation, we can say that on the addition of sodium hydroxide, the ferrous nitrate gives dirty green precipitates, and lead nitrate gives chalky white precipitates.

Note:
A common nitrate test is known as the brown ring test. On adding iron sulfate to a solution of nitrate and then adding concentrated sulphuric acid, a brown ring is formed at the junction of 2 layers. This indicates the presence of nitrate ions. To identify the presence of lead in a mixture, it can be treated with sodium hydroxide. A white precipitate is formed if it contains Pb (II).