Ionic equations: kick out the spectators

5 minAS Level2.3.2

AI-drafted, independently checked · not yet teacher-reviewed

By the end of this lesson

By the end you can write an ionic equation with state symbols, leaving out the spectator ions, and check that it balances in atoms and in charge.

Most of the ions are just watching

Mix silver nitrate solution with sodium chloride solution and a white solid appears instantly. But look at what actually changed: $\text{Ag}^+$ and $\text{Cl}^-$ grabbed each other. The $\text{Na}^+$ and $\text{NO}_3^-$ ions just floated about before and after, like the crowd at a football match.

An ionic equation shows only the ions that react. The bystanders are left out.

Definition

Spectator ions

Ions that are present in the reaction mixture but take no part in the reaction. They are unchanged, appearing identically on both sides of the full ionic equation, so they are left out of the ionic equation.

The four steps

Write the balanced full equation with state symbols.
Split every ionic substance that is (aq) into its ions. Strong acids count too: $\text{HCl(aq)}$ is $\text{H}^+\text{(aq)} + \text{Cl}^-\text{(aq)}$ .
Cancel ions that appear identically on both sides.
Check that atoms balance and total charge is the same on both sides.

Don't split solids (s), liquids (l) such as water, gases (g), or covalent molecules. They're not free ions.

Worked example: Silver chloride precipitate

Write the ionic equation for silver nitrate solution reacting with sodium chloride solution.

Have a go first?

Worked example: Any acid + any alkali

Write the ionic equation for hydrochloric acid neutralising sodium hydroxide solution.

Have a go first?

Quick check

Multiple choiceQuestion 1 · Recall

Barium chloride solution reacts with sodium sulfate solution:

$\text{BaCl}_2\text{(aq)} + \text{Na}_2\text{SO}_4\text{(aq)} \rightarrow \text{BaSO}_4\text{(s)} + 2\text{NaCl(aq)}$

Which is the ionic equation?

\text{Ba}^{2+}\text{(aq)} + \text{SO}_4^{2-}\text{(aq)} \rightarrow \text{BaSO}_4\text{(s)}

\text{Na}^+\text{(aq)} + \text{Cl}^-\text{(aq)} \rightarrow \text{NaCl(aq)}

\text{BaCl}_2\text{(aq)} + \text{SO}_4^{2-}\text{(aq)} \rightarrow \text{BaSO}_4\text{(s)} + 2\text{Cl}^-\text{(aq)}

\text{Ba}^{2+}\text{(aq)} + \text{SO}_4^{2-}\text{(aq)} \rightarrow \text{BaSO}_4\text{(aq)}

Answer the 3 questions above to continue.