Difficulty: Medium

Average Score: 61%

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 logarithmic, meaning each whole number change on the scale represents a tenfold change in acidity or alkalinity. Therefore, a pH of 3 indicates a concentration of hydrogen ions that is ten times greater than that of a pH of 4, making it 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 true, it does not accurately reflect the quantitative relationship between the two pH values. The correct answer specifies the degree of acidity difference, stating that a pH of 3 is ten times more acidic than a pH of 4, which is crucial for understanding the pH scale.

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

This statement is incorrect because the pH scale does not operate on a linear scale. A pH of 3 is not merely two times more alkaline than a pH of 4; rather, it is more acidic. The logarithmic nature of the pH scale means that the relationship between values is exponential, not additive.

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

This statement is also false. A pH of 3 is more acidic, not alkaline. The term "alkaline" refers to pH values above 7, while pH 3 and pH 4 are both acidic. Thus, this statement misinterprets the nature of pH values.

D (A substance with a pH of 3 is 10 times more acidic than a substance with a pH of 4.) CORRECT

This statement correctly reflects the logarithmic scale of pH, where each unit change represents a tenfold difference in acidity. Hence, a solution at pH 3 possesses a hydrogen ion concentration that is ten times greater than that of a solution at pH 4.

Conclusion

Understanding the pH scale is essential for assessing the acidity or alkalinity of substances. The logarithmic nature of the scale indicates that each unit change equates to a tenfold difference in hydrogen ion concentration. Thus, a substance with a pH of 3 is indeed ten times more acidic than one with a pH of 4, while the other options either misrepresent this relationship or incorrectly frame the concepts of acidity and alkalinity.

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