Difficulty: Easy

Average Score: 100%

Which of the following statements is correct regarding the pH scale?

Rationale

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

The pH scale is a logarithmic scale, which means each unit represents a tenfold change. A pH of 3 is therefore ten times more acidic than a pH of 4, not merely one unit or one time more acidic.

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

While this statement is technically true, it does not fully capture the quantitative relationship between these two pH values. Because the pH scale is logarithmic, a substance with a pH of 3 is not just more acidic than a substance with a pH of 4—it is ten times more acidic.

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

This statement is incorrect. A lower pH value means a substance is more acidic, not more alkaline. Therefore, a substance with a pH of 3 is more acidic, not more alkaline, than a substance with a pH of 4.

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

This statement is also incorrect. As previously mentioned, a lower pH value indicates a higher acidity. Therefore, a substance with a pH of 3 is ten times more acidic, not more alkaline, than a substance with a pH of 4.

Conclusion

The pH scale is a logarithmic scale, where each unit represents a tenfold difference. Therefore, a substance with a pH of 3 is ten times more acidic than a substance with a pH of 4. The other options are incorrect because they either improperly quantify the relationship between the two pH values or inaccurately characterize a lower pH value as indicating greater alkalinity rather than greater acidity. Understanding the nature of the pH scale is crucial for accurately interpreting and comparing acidity and alkalinity levels of different substances.

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