Chemistry 0.4 - Ionic equations

Chemistry 0.4 - Ionic equations

Higher tier: use a complete equation to identify unchanged spectator ions, then write an ionic equation that conserves both atoms and electrical charge.

Balanced ionic equations

A full symbol equation shows every reactant and product. A net ionic equation removes ions that remain unchanged and shows only the species involved in the chemical change.

When an ionic substance is aqueous, its ions can be written separately. Do not split a solid, a liquid or a gas into ions. An unchanged ion that appears in the same amount, with the same formula, charge and state on both sides is a spectator ion. It remains in the solution even though it cancels from the net equation.

Use this sequence:

  1. Write a balanced full symbol equation with state symbols.
  2. Separate the appropriate aqueous ionic substances into their ions, keeping all coefficients and charges.
  3. Cancel only spectator ions that are identical on both sides.
  4. Check that every element and the total electrical charge are conserved.

Worked example: forming silver chloride

At the macroscopic level, mixing the two colourless solutions produces a solid precipitate of silver chloride:

AgNOX3(aq)+NaCl(aq)→AgCl(s)+NaNOX3(aq)\ce{AgNO3(aq) + NaCl(aq) -> AgCl(s) + NaNO3(aq)}

Write the aqueous ionic substances as ions, but keep solid silver chloride together:

AgX+(aq)+NOX3X−(aq)+NaX+(aq)+ClX−(aq)→AgCl(s)+NaX+(aq)+NOX3X−(aq)\begin{aligned}\ce{Ag^+(aq) + NO3^-(aq) + Na^+(aq) + Cl^-(aq)}\\\ce{-> AgCl(s) + Na^+(aq) + NO3^-(aq)}\end{aligned}

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