Describe an activity to show that acids react with metal carbonates to give carbon dioxide. How will you test the gas?

1. 1 · State the rule in one line. Metal carbonate + acid → salt + carbon dioxide + water.
2. 2 · Describe the activity.
   • Take about 0.5 g of sodium carbonate in a test tube and add about 2 mL of dilute HCl.
   • Pass the gas through a delivery tube into lime water.
3. 3 · Draw the set-up. Draw a test tube with sodium carbonate and HCl, closed by a cork with a bent delivery tube. The tube dips into lime water in a second test tube. Label: dilute HCl, sodium carbonate, delivery tube, lime water, bubbles of CO₂.
4. 4 · Write the observations and equations.
   • Brisk effervescence; the lime water turns milky.
   • Na₂CO₃(s) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) + CO₂(g)
   • Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)
5. 5 · Add the result with excess gas. With excess CO₂ the milkiness goes: CaCO₃ + H₂O + CO₂ → Ca(HCO₃)₂, which dissolves.
6. 6 · Link to real life. Baking soda in dhokla batter reacts with sour curd or lemon to give CO₂, which makes it soft and spongy.
7. 7 · Close in one line. So all metal carbonates and hydrogencarbonates give CO₂ with acids.

Scoring tip: In the diagram, the delivery tube must dip below the surface of the lime water. Examiners check this.