Qualitative Salt Analysis: Carbonate ($$\text{CO}_3^{2-}$$)

Formula / Core Reaction:

$$\text{CO}_3^{2-} + 2\text{H}^+ \rightarrow \text{H}_2\text{O} + \text{CO}_2 \uparrow$$

$$\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 \downarrow \text{(Milky)} + \text{H}_2\text{O}$$

$$\text{CaCO}_3 + \text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{Ca(HCO}_3)_2 \text{ (Clear Solution)}$$

Concept: Reaction of carbonate salt with dilute $$\text{HCl}$$ evolves $$\text{CO}_2$$ gas, which turns lime water milky due to $$\text{CaCO}_3$$ formation. Excess $$\text{CO}_2$$ converts it into soluble calcium bicarbonate.

Notation / Key Observation:

• Effervescence: Colorless, odorless gas ($$\text{CO}_2$$);
• Milkiness disappears: Excess $$\text{CO}_2$$ forms soluble $$\text{Ca(HCO}_3)_2$$.