Question:What do you mean by a precipitation reaction? Explain by giving examples.
Answer:
Precipitation Reaction
A precipitation reaction is a type of chemical reaction in which two dissolved substances react to form at least one insoluble product, known as a Precipitate. This process typically involves a double displacement reaction where the anions and cations of two different reactants switch places, forming new compounds, one of which precipitates out of the solution because it is not soluble in water.
Examples of Precipitation Reaction
1. Reaction between Sodium Sulphate and Barium Chloride:
When an aqueous solution of sodium sulphate (Na₂SO₄) is mixed with an aqueous solution of barium chloride (BaCl₂), a white precipitate of barium sulphate (BaSO₄) is formed, while sodium chloride (NaCl) remains dissolved in the solution.
The chemical equation for this reaction is:
Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq)
Here, BaSO₄ is the white precipitate formed as a result of the reaction.
2. Reaction between Silver Nitrate and Sodium Chloride:
Adding an aqueous solution of silver nitrate (AgNO₃) to an aqueous solution of sodium chloride (NaCl) results in the formation of a white precipitate of silver chloride (AgCl), with sodium nitrate (NaNO₃) remaining in the solution.
The chemical equation for this reaction is:
AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
In this case, AgCl is the white precipitate. It’s noteworthy that AgCl can further undergo a photochemical reaction in the presence of sunlight, decomposing into metallic silver (Ag) and chlorine gas (Cl₂), which is utilised in photographic films and papers. This decomposition is evidenced by the discoloration of white AgCl to grey due to the formation of silver metal.
