When hydrochloric acid is slowly added to sodium hydroxide solution, how will the pH of the solution change?
Answer and explanation
Correct answer: pH will decrease and become about 7 near neutralisation
The governing concept is neutralisation and the logarithmic pH scale. Sodium hydroxide initially makes the solution basic, so its pH is above 7. As hydrochloric acid is added, hydrogen ions reduce the hydroxide concentration and the pH falls. At the equivalence point, equal reacting amounts of strong acid and strong base produce nearly neutral sodium chloride solution, with pH about 7. Therefore C is correct; A and D show the wrong trend.
Frequently asked questions
What is the correct answer to this question?
pH will decrease and become about 7 near neutralisation
Why is this the correct answer?
The governing concept is neutralisation and the logarithmic pH scale. Sodium hydroxide initially makes the solution basic, so its pH is above 7. As hydrochloric acid is added, hydrogen ions reduce the hydroxide concentration and the pH falls. At the equivalence point, equal reacting amounts of strong acid and strong base produce nearly neutral sodium chloride solution, with pH about 7. Therefore C is correct; A and D show the wrong trend.
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.
