Chemistry / Unit 3 Chem 0468 worked example, 60 to 90 seconds
Classifying a Reaction as Precipitation, Acid-Base, or Redox
The idea
Classifying a reaction means checking, in order, whether ions combine to form an insoluble solid, whether a hydrogen ion transfers between species, or whether any oxidation number changes.
In practice
A reaction between silver nitrate and sodium chloride forms solid AgCl with no charge changes on any element — a precipitation reaction. A reaction between HCl and NaOH transfers H+ from acid to base with no oxidation-number changes — an acid-base reaction. A reaction between zinc metal and copper sulfate changes zinc's oxidation number from 0 to +2 and copper's from +2 to 0 — a redox reaction, specifically single-displacement.
Where people slip
A reaction can show more than one surface feature at once; oxidation-number change is the deciding test whenever a reaction looks like it could fit two categories.
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