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Take two test tubes. Mark them as ‘A’ and ‘B’. Take about 0.5 gm of sodium carbonate in the test tube ‘A’ and 0.5 gm of sodium hydrogen carbonate in test tube ‘B’. Add about 2 ml of dilute HCl acid to both test tubes. Pass the gas produced in each case through lime water as shown in the figure. Lime water in each case will turn milky due to the production of CO₂ gas in each of the test tubes.

Reactions occurring in the above activity:

Tet tube ‘A’ Na₂CO₃ (s) + 2HCl (aq) → 2Na2NaCl (aq) + CO₂ (g) + H₂O(l)

Test tube ‘B’ NaHCO₃(s) + HCl (aq) → NaCl (aq) + CO₂(g) + H₂O (l)

On passing the gas evolved through the lime water:

But on passing excess CO₂ gas through the lime waster, milkiness disappears due to the formation of soluble CaHCO₃

This activity shows that metal carbonates and metal hydrogen carbonates react with acids to form salt, CO₂ and water.