Describe an activity to show that acids react with metal carbonates and hydrogen carbonates to give carbon dioxide. Write the equations, including the test for the gas and what happens with excess gas.

1. 1 · State the reaction. Metal carbonate (or hydrogen carbonate) + acid → salt + water + carbon dioxide.
2. 2 · Set up. Put sodium carbonate in a boiling tube with a thistle funnel and a delivery tube dipping into lime water. Pour dilute HCl down the funnel.
3. 3 · Draw the set-up. Draw the boiling tube, thistle funnel, cork, delivery tube and a test tube of lime water, and label each part.
4. 4 · Observe and write equations.
   • Brisk fizzing: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂
   • With NaHCO₃: NaHCO₃ + HCl → NaCl + H₂O + CO₂
   • Lime water turns milky: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
5. 5 · Excess gas. The milkiness disappears: CaCO₃ + H₂O + CO₂ → Ca(HCO₃)₂, which dissolves.
6. 6 · Real life. Egg shells and marble are calcium carbonate, so they fizz with acids.
7. 7 · Close in one line. So all carbonates and hydrogen carbonates give carbon dioxide with acids.

Scoring tip: Draw the delivery tube dipping below the surface of the lime water. Balance every equation: a missing 2 before HCl loses the mark.