If the pH of a solution changes from 2 to 5, what happens to the hydrogen ion concentration?
Answer and explanation
Correct answer: It will decrease one thousand times
The governing relation is pH = −log₁₀[H⁺]. A rise of one pH unit means a tenfold decrease in hydrogen-ion concentration. The change from pH 2 to pH 5 is three units, so [H⁺] changes by 10³ = 1000 in the decreasing direction. For example, 10⁻² mol L⁻¹ becomes 10⁻⁵ mol L⁻¹. Therefore option A is correct; it is not merely a threefold change.
Frequently asked questions
What is the correct answer to this question?
It will decrease one thousand times
Why is this the correct answer?
The governing relation is pH = −log₁₀[H⁺]. A rise of one pH unit means a tenfold decrease in hydrogen-ion concentration. The change from pH 2 to pH 5 is three units, so [H⁺] changes by 10³ = 1000 in the decreasing direction. For example, 10⁻² mol L⁻¹ becomes 10⁻⁵ mol L⁻¹. Therefore option A is correct; it is not merely a threefold change.
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.
