An aqueous solution of sodium carbonate is alkaline because sodium carbonate is a salt of — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

# Analysis of Sodium Carbonate's Alkalinity **Step 1: Identify the salt composition** $Na_2CO_3$ is formed from: - Strong base: $NaOH$ (sodium hydroxide) - Weak acid: $H_2CO_3$ (carbonic acid) **Step 2: Apply salt hydrolysis concept** When a salt of a strong base and weak acid dissolves in water, the anion undergoes hydrolysis: $$CO_3^{2-} + H_2O \rightleftharpoons HCO_3^- + OH^-$$ **Step 3: Explain alkalinity** The carbonate ion ($CO_3^{2-}$) accepts protons from water molecules, producing hydroxide ions ($OH^-$), which makes the solution alkaline (pH > 7). **Step 4: Why other options are wrong** - If it were a salt of strong acid + strong base → neutral solution (no hydrolysis) - If it were a salt of weak base + strong acid → acidic solution - If it were a salt of weak acid + weak base → depends on relative strengths **Answer: C — A salt of a strong base and weak acid** The weak carbonate ion hydrolyzes to produce $OH^-$ ions, causing the alkaline nature of the solution.