When solid calcium carbonate reacts with hydrochloric acid, keep CaCO₃(s) together on the reactant side of the ionic equation. Write the acid as hydrogen and chloride ions. Chloride is unchanged and cancels, while calcium appears as an aqueous ion on the product side.
SEC 2027 G3 Chemistry (K324) covers ionic equations and reactions of acids with carbonates. The worked comparison below shows why a solid carbonate and a dissolved carbonate give different net ionic equations even though both release carbon dioxide.
- Write and balance the full equation with state symbols.
- Use the physical state to decide what to write as separate ions.
- Check atoms and total charge after cancelling spectators.
Worked example | Calcium carbonate and hydrochloric acid
The balanced equation is CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + CO₂(g) + H₂O(l). The calcium carbonate begins as a solid. The calcium chloride is in solution in this example.
In the full ionic equation, write CaCO₃(s) + 2H⁺(aq) + 2Cl⁻(aq) → Ca²⁺(aq) + 2Cl⁻(aq) + CO₂(g) + H₂O(l). The chloride ions are present in the same form and amount on both sides.
After cancelling chloride, the net equation is CaCO₃(s) + 2H⁺(aq) → Ca²⁺(aq) + CO₂(g) + H₂O(l). Count one calcium, one carbon, three oxygen and two hydrogen atoms on each side. The total charge is +2 on each side.
Compare it with dissolved sodium carbonate
When sodium carbonate is dissolved in water, Na⁺(aq) and CO₃²⁻(aq) can be written separately. With hydrochloric acid, sodium and chloride are spectators in this example. The net equation is CO₃²⁻(aq) + 2H⁺(aq) → CO₂(g) + H₂O(l).
Compare the left sides. The first equation records the consumption of solid calcium carbonate and the release of calcium ions. The second starts with carbonate ions already in solution. Both produce the same gas.
Repair the equation before checking charge
A pupil writes CO₃²⁻(aq) + H⁺(aq) → CO₂(g) + H₂O(l) for solid calcium carbonate. There are two repairs. First restore CaCO₃(s) on the left and Ca²⁺(aq) on the right. Then use 2H⁺ to supply the two hydrogen atoms in water and balance charge.
Try the soluble sodium carbonate case next. The aqueous carbonate ion belongs on the left in that case. Ask a study partner to explain the difference using the state symbols before either of you checks the coefficients.
Frequently asked questions
Do all ionic compounds split into ions in an ionic equation?
Use the state and the species present in the question. Keep a solid such as CaCO₃(s) intact in the equation for this reaction.
Why does calcium stay in the net equation?
It begins in the solid and ends as an aqueous ion. It has not stayed in the same form.
Official information
SEAB’s 2027 SEC G3 Chemistry syllabus (K324), Chemical Calculations and Acids, Bases and Salts. Checked 9 November 2026.