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Chemistry · Glossary

What is Spectator ion?

Definition 19.2 School Chemistry — Grades 1 to 12 · Chapter 19 — Metals: Reactions with Acids and Corrosion

An ion that is present in a solution during a reaction but takes no part in it, and is found unchanged at the end, is a spectator ion. It is left out of the equation.

Examples

Example 19.3 (Iron and zinc in hydrochloric acid)

Hydrochloric acid contains HX+(aq)\ce{H+(aq)} and ClX−(aq)\ce{Cl-(aq)} ions. The chloride ions are found unchanged at the end: they are spectators. The equations are

Fe(s)+2 HX+(aq)→FeX2+(aq)+HX2(g),Zn(s)+2 HX+(aq)→ZnX2+(aq)+HX2(g).\ce{Fe(s) + 2H+(aq) -> Fe^{2+}(aq) + H2(g)}, \qquad \ce{Zn(s) + 2H+(aq) -> Zn^{2+}(aq) + H2(g)}.

They balance both the atoms and the charges: +2+2 on each side.

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