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
An acidic solution contains a relatively high concentration of hydrogen or hydronium ions. Added hydroxide ions react with them in the neutralisation step: H⁺ + OH⁻ → H₂O. This lowers the hydrogen-ion concentration. Since pH = −log[H⁺], a decrease in [H⁺] produces an increase in pH. The ions do not increase acidity or form carbon dioxide, so option 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?
An acidic solution contains a relatively high concentration of hydrogen or hydronium ions. Added hydroxide ions react with them in the neutralisation step: H⁺ + OH⁻ → H₂O. This lowers the hydrogen-ion concentration. Since pH = −log[H⁺], a decrease in [H⁺] produces an increase in pH. The ions do not increase acidity or form carbon dioxide, so option 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.
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