How does the pH change when hydrochloric acid is gradually added to sodium hydroxide solution?
Answer and explanation
Correct answer: It decreases from high value to near 7 and then below 7
Sodium hydroxide is a base, so its initial pH is above 7. Adding hydrochloric acid supplies hydrogen ions that neutralise hydroxide ions: H⁺ + OH⁻ → H₂O. The pH therefore falls toward 7 near the equivalence point. If more acid is added after neutralisation, excess hydrogen ions make the solution acidic and the pH drops below 7. Hence A is correct.
Frequently asked questions
What is the correct answer to this question?
It decreases from high value to near 7 and then below 7
Why is this the correct answer?
Sodium hydroxide is a base, so its initial pH is above 7. Adding hydrochloric acid supplies hydrogen ions that neutralise hydroxide ions: H⁺ + OH⁻ → H₂O. The pH therefore falls toward 7 near the equivalence point. If more acid is added after neutralisation, excess hydrogen ions make the solution acidic and the pH drops below 7. Hence 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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