By Jack Brubaker
Updated Mar 24, 2022

Water

Water (H₂O) undergoes autodissociation, a self‑ionization process that splits it into hydrogen ions (H⁺) and hydroxide ions (OH^-):

H₂O → H⁺ + OH^-

pH

The pH scale quantifies the concentration of H⁺ in a solution, ranging from 0 to 14. A pH >7 denotes an alkaline (basic) solution, <7 indicates acidity, and 7 represents neutrality.

Sodium Carbonate

Sodium carbonate (Na₂CO₃), commonly known as washing soda, dissociates in water to release sodium ions (Na⁺) and carbonate ions (CO₃^2‑):

Na₂CO₃ → 2 Na⁺ + CO₃^2‑

The Na⁺ ions are spectator ions and do not affect pH. In contrast, CO₃^2‑ reacts with water, generating hydroxide ions and thereby raising the solution’s pH:

CO₃^2‑ + H₂O → HCO₃^- + OH^-

Concentration and pH

pH is directly proportional to the concentration of dissolved sodium carbonate. For example, adding two tablespoons of Na₂CO₃ to a glass of water produces a higher pH than adding one tablespoon, because the greater ionic strength increases OH^- concentration.

Mixing Instructions

Scientific measurements confirm the following pH values for standardized solutions:

• 1 g (0.035 oz) of Na₂CO₃ dissolved and diluted to 1 L (≈1 quart) → pH = 11.37
• 5 g (0.18 oz) of Na₂CO₃ dissolved and diluted to 1 L (≈1 quart) → pH = 11.58
• 10 g (0.35 oz) of Na₂CO₃ dissolved and diluted to 1 L (≈1 quart) → pH = 11.70