A student takes equal amounts of two acids. The first ionises completely and the second ionises partially. Which is more likely to have a lower pH?
Answer and explanation
Correct answer: The first acid
For equal amounts and comparable concentrations, pH depends on the hydrogen-ion concentration, according to pH = −log[H⁺]. Complete ionisation releases a greater proportion of hydrogen ions than partial ionisation, so the first acid is more likely to have the larger [H⁺] and therefore the lower pH. Option A is correct. The second acid would generally have a higher pH, while neither acid is necessarily neutral.
Frequently asked questions
What is the correct answer to this question?
The first acid
Why is this the correct answer?
For equal amounts and comparable concentrations, pH depends on the hydrogen-ion concentration, according to pH = −log[H⁺]. Complete ionisation releases a greater proportion of hydrogen ions than partial ionisation, so the first acid is more likely to have the larger [H⁺] and therefore the lower pH. Option A is correct. The second acid would generally have a higher pH, while neither acid is necessarily neutral.
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.
