- Take two test tubes, label them as A and B.
- Take about 0.5 g of sodium carbonate (Na2CO3) in test tube A and about 0.5 g of sodium hydrogen carbonate (NaHCO3) in test tube B.
- Add about 2 mL of dilute HCl to both test tubes.
- What do you observe?
✅ Answer: CO2 gas is produced in both test tubes.
Test tube A:
Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g)
Test tube B:
NaHCO3(s) + HCl(aq) → NaCl(aq) + H2O(l) + CO2(g)
- Pass the gas produced in each case through lime water (calcium hydroxide solution) as shown in Fig. 2.2 and record your observations.
✅ Answer: On passing CO2 through lime water (calcium hydroxide), lime water becomes milky.
Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
(Lime water) (White precipitate)
On passing excess CO2, lime water becomes clear due to the formation of soluble calcium bicarbonate.
CaCO3(s)+ H2O(l)+ CO2(g) →Ca(HCO3)2(aq)
(Soluble in water)