Science (086) — AI-generated practice question

Precipitation Reaction involves two aqueous solutions reacting through an exchange of ions (double displacement). The insoluble solid forms because the exchanged ions combine to create an insoluble salt.

Example: Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq)
Here, Ba²⁺ and SO₄²⁻ ions exchange and form insoluble barium sulphate.

Decomposition Reaction involves a single compound breaking down into two or more simpler substances upon supply of energy (heat, light, or electricity).

Example: CaCO₃(s) → CaO(s) + CO₂(g)
The insoluble solid (CaO) is produced from the breakdown of one reactant.

Key distinction: Precipitation requires two reactants and ion exchange; decomposition requires only one reactant and an energy input.

Source: Chapter 1, Section 1.2 / 1.2.4

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• The question specifically says not to distinguish by counting reactants/products — so you must mention ion exchange (for precipitation) and energy input / single reactant breaking down (for decomposition).
• Examiners look for: correct examples with equations, and a clear conceptual distinction about the nature of reactants and the process.
• Precipitation is a sub-type of double displacement; always mention ion exchange.
• For decomposition, mentioning energy supply (heat/light/electricity) strengthens the answer.