Which of the following is correct regarding the pH scale?
A.
A substance with a pH of 3 is two times more alkaline than a substance with a pH of 4.
B.
A substance with a pH of 3 is two times more acidic than a substance with a pH of 4.
C.
A substance with a pH of 3 is 10 times more acidic than a substance with a pH of 4.
D.
A substance with a pH of 3 is 10 times more alkaline than a substance with a pH of 4.
The correct answer and Explanation is :
The correct answer is:
C. A substance with a pH of 3 is 10 times more acidic than a substance with a pH of 4.
Explanation:
The pH scale measures the acidity or alkalinity of a substance, with a range from 0 to 14. A pH of 7 is considered neutral, with values below 7 indicating acidity and values above 7 indicating alkalinity.
The pH scale is logarithmic, meaning each whole number change on the scale represents a tenfold change in acidity or alkalinity. This means that a substance with a pH of 3 is ten times more acidic than a substance with a pH of 4.
Here’s a breakdown of why this is the case:
- Logarithmic Nature of the pH Scale: The pH scale is based on the concentration of hydrogen ions (H⁺) in a solution. The formula for pH is:
[
\text{pH} = -\log[\text{H}^+]
]
This means that each unit change in pH represents a tenfold change in the concentration of hydrogen ions. For example, a pH of 3 means that the hydrogen ion concentration is (10^{-3}) M, while a pH of 4 means it is (10^{-4}) M. - Comparing pH 3 and pH 4: To determine how much more acidic one solution is compared to another, you calculate the ratio of their hydrogen ion concentrations. For pH 3 and pH 4:
[
\text{Ratio} = \frac{[\text{H}^+]{\text{pH 3}}}{[\text{H}^+]{\text{pH 4}}} = \frac{10^{-3}}{10^{-4}} = 10
]
Therefore, a solution with a pH of 3 has ten times more hydrogen ions than a solution with a pH of 4, making it ten times more acidic. - Misconceptions: The other options are incorrect because they misinterpret the logarithmic nature of the pH scale. For instance, a pH of 3 is not two times more alkaline or two times more acidic than a pH of 4; the actual difference is tenfold.
In summary, the pH scale’s logarithmic nature means that a change of one unit corresponds to a tenfold difference in acidity or alkalinity. Thus, a substance with a pH of 3 is ten times more acidic than one with a pH of 4.