If the hydrogen ion concentration in a solution increases ten times, what happens to the pH?
Answer and explanation
Correct answer: pH decreases by one unit
The governing concept is the logarithmic definition of pH: pH = −log₁₀[H⁺]. If the hydrogen-ion concentration changes from [H⁺] to 10[H⁺], the new value is −log₁₀(10[H⁺]) = −1 − log₁₀[H⁺], so the pH falls by exactly one unit. Acidity therefore increases. Option A is correct; a tenfold concentration change does not produce a ten-unit or positive pH change.
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What is the correct answer to this question?
pH decreases by one unit
Why is this the correct answer?
The governing concept is the logarithmic definition of pH: pH = −log₁₀[H⁺]. If the hydrogen-ion concentration changes from [H⁺] to 10[H⁺], the new value is −log₁₀(10[H⁺]) = −1 − log₁₀[H⁺], so the pH falls by exactly one unit. Acidity therefore increases. Option A is correct; a tenfold concentration change does not produce a ten-unit or positive pH 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.
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