* Hydrolysis: When sodium carbonate dissolves in water, it undergoes hydrolysis. This means the carbonate ions (CO₃²⁻) react with water molecules to form bicarbonate ions (HCO₃⁻) and hydroxide ions (OH⁻). The presence of hydroxide ions makes the solution basic.

* Weak acid, strong base: Sodium carbonate is formed from the reaction of a strong base (sodium hydroxide, NaOH) and a weak acid (carbonic acid, H₂CO₃). Salts derived from strong bases and weak acids are typically basic.

The reaction in water:

Na₂CO₃(s) + H₂O(l) ⇌ 2Na⁺(aq) + HCO₃⁻(aq) + OH⁻(aq)

The presence of hydroxide ions (OH⁻) is what makes the solution basic.