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

💡 Solution & Explanation

# Salt Hydrolysis and Alkalinity of $Na_2CO_3$ **Step 1: Identify the salt components** $Na_2CO_3$ is composed of: - $Na^+$ (from strong base NaOH) - $CO_3^{2-}$ (from weak acid $H_2CO_3$) **Step 2: Analyze cation behavior** $Na^+$ is the conjugate acid of a strong base (NaOH), so it **does not hydrolyze** and doesn't affect pH. **Step 3: Analyze anion behavior** $CO_3^{2-}$ is the conjugate base of a weak acid ($HCO_3^-$), so it **undergoes hydrolysis**: $$CO_3^{2-} + H_2O \rightleftharpoons HCO_3^- + OH^-$$ **Step 4: Determine pH effect** Hydrolysis of $CO_3^{2-}$ produces $OH^-$ ions, making the solution **basic/alkaline**. **Answer: C — A salt of a weak acid and a strong base** $Na_2CO_3$ is alkaline because it's a salt formed from a **weak acid** ($H_2CO_3$) and a **strong base** (NaOH). The anion hydrolyzes to produce hydroxide ions, increasing the solution's pH above 7.