The strength of an alkali is determined by its ability to donate hydroxide ions (OH-) in water. The more hydroxide ions an alkali can donate, the stronger it is.
Caustic soda is a highly soluble base that dissociates completely in water to form sodium ions (Na+) and hydroxide ions (OH-). It has a pH of around 13, which indicates a high concentration of hydroxide ions.
On the other hand, soda ash is a moderately soluble salt that undergoes partial dissociation in water. It forms sodium ions (Na+) and carbonate ions (CO32-). The carbonate ions can react with water to form bicarbonate ions (HCO3-) and hydroxide ions (OH-), but the concentration of hydroxide ions is lower compared to caustic soda. The pH of a saturated soda ash solution is around 11.
Therefore, caustic soda is considered a stronger alkali than soda ash due to its higher hydroxide ion concentration and greater ability to raise the pH of a solution.
