pH of water is 7.0 at 25°C. If water is heated to 70°C, the — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

The auto-ionization of water ($H_2O$ ⇌ H+ + OH-) is an endothermic process. According to Le Chatelier's principle, increasing the temperature shifts the equilibrium to the right, which increases Kw. This increases both [H+] and [OH-] simultaneously. Since pH = -log[H+], the pH decreases below 7.0. However, since [H+] still equals [OH-], the water remains chemically neutral.