Carboxyl Group Detection ($$-\text{COOH}$$)

Formula / Core Reaction:

$$\text{R-COOH} + \text{NaHCO}_3 \rightarrow \text{R-COONa} + \text{H}_2\text{O} + \text{CO}_2 \uparrow$$

Concept: Carboxylic acids are sufficiently acidic ($$\text{p}K_a \approx 4-5$$) to decompose sodium bicarbonate ($$\text{NaHCO}_3$$), releasing carbon dioxide gas as brisk effervescence.

Notation / Key Observation:

• $$\text{NaHCO}_3$$: Sodium bicarbonate;
• $$\text{CO}_2 \uparrow$$: Brisk effervescence (turns lime water milky).