Difficulty: Easy

Average Score: 92%

Which of the following is correct regarding the pH scale?

Rationale

A substance with a pH of 3 is 10 × more acidic than a substance with a pH of 4.

The pH scale is logarithmic, meaning that each whole number change on the scale represents a tenfold increase or decrease in acidity or alkalinity. Therefore, a pH of 3 is ten times more acidic than a pH of 4.

A (A substance with a pH of 3 is 10 × more alkaline than a substance with a pH of 4.) YOUR ANSWER

This statement is incorrect because it incorrectly describes the relationship between pH values. A lower pH indicates higher acidity, not alkalinity, so a substance with a pH of 3 cannot be more alkaline than one with a pH of 4.

B (A substance with a pH of 3 is two × more alkaline than a substance with a pH of 4.) YOUR ANSWER

This choice is also incorrect as it misrepresents the concept of acidity and alkalinity. Since pH 3 indicates higher acidity than pH 4, it cannot be described as more alkaline in any measure.

C (A substance with a pH of 3 is two × more acidic than a substance with a pH of 4.) YOUR ANSWER

This option is misleading because while a pH of 3 is indeed more acidic than a pH of 4, the change in acidity is not a factor of two; it is a tenfold increase in acidity, according to the logarithmic nature of the pH scale.

Conclusion

The pH scale operates on a logarithmic basis, where each unit change reflects a tenfold difference in acidity or alkalinity. Thus, a pH of 3 is ten times more acidic than a pH of 4, making option D the only accurate statement regarding the pH scale. Understanding this relationship is crucial for accurately interpreting and applying pH measurements in various scientific contexts.

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