Why does pH increase when hydroxide ions are added to an acidic solution?
Answer and explanation
Correct answer: They combine with hydrogen ions to form water
The governing concept is neutralisation and the definition of pH. An acidic solution contains an excess of hydrogen or hydronium ions. Added hydroxide ions react with them to form water: H₃O⁺ + OH⁻ → 2H₂O, or equivalently H⁺ + OH⁻ → H₂O. This lowers hydrogen-ion concentration, and because pH = −log[H⁺], the pH rises. The other options do not describe neutralisation, so A is correct.
Frequently asked questions
What is the correct answer to this question?
They combine with hydrogen ions to form water
Why is this the correct answer?
The governing concept is neutralisation and the definition of pH. An acidic solution contains an excess of hydrogen or hydronium ions. Added hydroxide ions react with them to form water: H₃O⁺ + OH⁻ → 2H₂O, or equivalently H⁺ + OH⁻ → H₂O. This lowers hydrogen-ion concentration, and because pH = −log[H⁺], the pH rises. The other options do not describe neutralisation, so A is correct.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
