Answer
🧪 pH and Hydrogen Ion Concentration
Question
A decrease in the H⁺ concentration by a factor of 100 implies which of the following?
✅ A. The pH increases by 2.
Step-by-Step Explanation
The pH is defined as:
pH = -log[H⁺]If the hydrogen ion concentration decreases by a factor of 100:
[H⁺]new = [H⁺]original / 100 = [H⁺] × 10⁻²This results in an increase in pH by:
pH increases by log(100) = 2So the pH becomes:
pHnew = pHoriginal + 2Why the Other Options Are Incorrect
| Option | Explanation |
|---|---|
| B. The pH decreases by 2. | Incorrect — this would imply [H⁺] increased 100x |
| C. The pH increases by a factor of 100. | Incorrect — pH is logarithmic, not linear |
| D. The pH decreases by a factor of 100. | Incorrect — this misinterprets the relationship between [H⁺] and pH |
Key Concept Recap
- pH is the negative log of the hydrogen ion concentration.
- A 10-fold change in [H⁺] changes pH by 1 unit.
- A 100-fold decrease in [H⁺] increases pH by 2 units.