Question: Write the reaction involved in Kolbe's reaction.

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Step 1 (Reaction Conditions and Reactants): [0.5 Mark]

Kolbe's reaction involves the treatment of phenol with sodium hydroxide ($NaOH$) to form sodium phenoxide, which then undergoes electrophilic substitution with carbon dioxide ($CO_2$) under pressure ($4-7 \text{ atm}$) and temperature ($393 \text{ K}$), followed by acidification.

Step 2 (Chemical Equation): [0.5 Mark]

The balanced chemical equation for the formation of Salicylic acid (2-hydroxybenzoic acid) is:

$$ \text{C}_6\text{H}_5\text{OH} \xrightarrow[2. \text{ H}^+]{1. \text{ NaOH, CO}_2, 393\text{K}, 4-7\text{atm}} \text{C}_6\text{H}_4(\text{OH})(\text{COOH}) $$

Or, represented structurally:

$$ \text{Phenol} \xrightarrow[2. \text{ H}_3\text{O}^+]{1. \text{ NaOH, CO}_2} \text{Salicylic acid} $$

Step 3 (Final Concluded Answer): [Full Marks]

The reaction converts phenol into 2-hydroxybenzoic acid (salicylic acid) via the carboxylation of the phenoxide ion.

💡 EL10 Concept Insight: Think of this reaction as "tagging" a phenol molecule with a carbon dioxide molecule to turn it into a medicinal acid; the base makes the phenol reactive enough to grab the $CO_2$ gas, which then sticks to the ring to form salicylic acid.