If one solution has one hundred times more hydrogen ions than another solution, by how much will its pH be lower approximately?
Answer and explanation
Correct answer: Two units
The governing concept is the logarithmic definition of pH: pH = −log₁₀[H⁺]. If the hydrogen-ion concentration becomes 10 times larger, pH decreases by 1 unit. A hundredfold increase is 10², so the decrease is log₁₀(100) = 2 units. The change is therefore not 100 units and cannot be zero. Assuming comparable conditions and activities, option A gives the correct approximate difference.
Frequently asked questions
What is the correct answer to this question?
Two units
Why is this the correct answer?
The governing concept is the logarithmic definition of pH: pH = −log₁₀[H⁺]. If the hydrogen-ion concentration becomes 10 times larger, pH decreases by 1 unit. A hundredfold increase is 10², so the decrease is log₁₀(100) = 2 units. The change is therefore not 100 units and cannot be zero. Assuming comparable conditions and activities, option A gives the correct approximate difference.
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.
