Precipitation reaction and net ionic equation
In a precipitation reaction, two soluble salts react and an insoluble solid, the precipitate, forms. A net ionic equation shows only the ions that change, leaving out the spectator ions that stay dissolved.
Last updated
Analogy
At a party, only two guests who were strangers end up pairing off. Everyone else just watches.
Example
Full: Ag⁺ + NO₃⁻ + Na⁺ + Cl⁻ → AgCl(s) + Na⁺ + NO₃⁻Spectators: Na⁺, NO₃⁻Net: Ag⁺(aq) + Cl⁻(aq) → AgCl(s)
In practice
Water treatment plants add chemicals that make unwanted metal ions form solids, which can then be filtered out.
Practice
Flashcards
- What is a spectator ion?An ion that is in solution but unchanged by the reaction.
Questions people ask
How do I know if a precipitate will form?
Use the solubility rules. Almost all nitrates and group 1 salts are soluble. Most chlorides are soluble except AgCl, PbCl₂ and Hg₂Cl₂. Most carbonates, phosphates and hydroxides are insoluble. If swapping partners gives an insoluble compound, a precipitate forms. Always check this against a solubility table in your course notes.
What is a spectator ion?
A spectator ion is present in the solution but does not take part in the reaction. It appears unchanged on both sides of the full ionic equation, so it is removed to write the net ionic equation. In the silver chloride example, sodium and nitrate ions are the spectators.