Question 22

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 in pH represents a tenfold change in acidity or alkalinity. Therefore, a substance with a pH of 3 is indeed 10 times more acidic than one with a pH of 4.

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

While this statement is true, it does not quantify the difference in acidity. It simply states that pH 3 is more acidic than pH 4 without explaining the relationship in terms of tenfold change, which is critical in 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.

This statement is incorrect. The pH scale does not operate on a linear scale, and a lower pH value indicates a higher acidity, not alkalinity. Therefore, pH 3 cannot be described as more alkaline compared to pH 4.

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

This statement is also incorrect. Similar to option B, it misrepresents the relationship between pH values. A lower pH value indicates higher acidity, not alkalinity, making this statement fundamentally flawed.

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

This statement is correct. The pH scale indicates that each unit change represents a tenfold increase or decrease in hydrogen ion concentration, thus making a pH of 3 ten times more acidic than a pH of 4.

Conclusion

The correct answer is option D because it accurately reflects the logarithmic nature of the pH scale, where each unit represents a tenfold difference in acidity. Options A, B, and C fail to provide this crucial information or misrepresent the relationship, emphasizing the importance of understanding the pH scale's logarithmic characteristics.