Questions on pH and Calculating pH
20 Multiple-Choice Questions on pH and Calculating pH
1. What is the definition of pH?
A) The concentration of hydroxide ions
B) The negative logarithm of hydroxide ion concentration
C) The negative logarithm of hydrogen ion concentration
D) The sum of hydrogen and hydroxide ion concentrations
E) The measure of solution density
2. What is the pH of a solution with [H⁺] = 1.0 × 10⁻³ M?
A) 3
B) 11
C) 7
D) 0.003
E) 10
3. If the pH of a solution is 8, what is the concentration of H⁺ ions?
A) 1.0 × 10⁻⁸ M
B) 8 M
C) 1.0 × 10⁻⁶ M
D) 8 × 10⁻¹⁴ M
E) 1.0 × 10⁻⁷ M
4. Which equation correctly relates pH and [H⁺]?
A) pH = log[H⁺]
B) pH = –log[H⁺]
C) pH = [H⁺] × 10
D) pH = –ln[H⁺]
E) pH = 1 / [H⁺]
5. What is the pH of pure water at 25°C?
A) 0
B) 7
C) 14
D) 1
E) 10
6. A solution has a pH of 4. What is the [H⁺]?
A) 4 M
B) 1.0 × 10⁻⁴ M
C) 4 × 10⁻⁴ M
D) 1.0 × 10⁴ M
E) 1.0 × 10⁻¹⁰ M
7. How would you calculate the pH of a solution with [OH⁻] = 1.0 × 10⁻⁵ M at 25°C?
A) pH = 5
B) pH = 9
C) pH = 14 – 5 = 9
D) pH = –log(1.0 × 10⁻⁵)
E) Both B and C are correct
8. What is the pH of a solution where [H⁺] = 1.0 × 10⁻¹² M?
A) 12
B) 2
C) 1.2
D) 10⁻¹²
E) 0.12
9. If the pH of a solution decreases from 6 to 3, the concentration of H⁺:
A) Decreases by 3 times
B) Increases by 3 times
C) Decreases by 1000 times
D) Increases by 1000 times
E) Remains the same
10. What is the pH of a solution with [OH⁻] = 1.0 × 10⁻⁹ M at 25°C?
A) 5
B) 9
C) 14
D) 6
E) 4
11. Which pH value corresponds to a neutral solution at 25°C?
A) 1
B) 7
C) 14
D) 0
E) 10
12. What is the relationship between pH and pOH?
A) pH + pOH = 7
B) pH × pOH = 14
C) pH + pOH = 14
D) pH = pOH
E) pH – pOH = 14
13. The pOH of a solution is 3. What is the pH?
A) 3
B) 7
C) 11
D) 14
E) 17
14. What is the pH of a 0.01 M HCl solution?
A) 2
B) 12
C) 0.01
D) 10
E) 4
15. For a solution with pH = 9, which is true?
A) It is acidic
B) It is neutral
C) It is basic
D) [H⁺] = 10⁻⁹ M
E) Both C and D
16. How do you find the [H⁺] concentration if pH = 5?
A) 5 M
B) 1 × 10⁵ M
C) 1 × 10⁻⁵ M
D) 5 × 10⁻¹ M
E) –5 M
17. If [H⁺] = 3.2 × 10⁻⁴ M, the pH is approximately:
A) 3.49
B) 4
C) 2.5
D) 3.0
E) 0.00032
18. A solution’s pH is 11. What is the [OH⁻]?
A) 1 × 10⁻³ M
B) 1 × 10⁻¹¹ M
C) 1 × 10⁻⁴ M
D) 1 × 10⁻¹ M
E) 11 M
19. Which of the following has the highest pH?
A) Vinegar (pH ~3)
B) Lemon juice (pH ~2)
C) Milk (pH ~6.5)
D) Ammonia solution (pH ~11)
E) Distilled water (pH 7)
20. What is the pH of a solution with [H⁺] = 5.0 × 10⁻⁵ M?
A) 4.3
B) 5.0
C) 3.7
D) 9.3
E) 7.0
- Questions on Brønsted-Lowry Acids and Bases
- Questions on Lewis Acids and Bases
- Questions on Self-Ionization of Water (Kw)
Answer Key with Explanations
1. C – pH = –log[H⁺].
2. A – pH = –log(1.0 × 10⁻³) = 3.
3. A – pH = 8 → [H⁺] = 10⁻⁸ M.
4. B – pH = –log[H⁺].
5. B – Pure water at 25°C is neutral, pH = 7.
6. B – pH = –log(1.0 × 10⁻⁴) = 4.
7. E – pOH = –log[OH⁻] = 5, so pH = 14 – 5 = 9.
8. A – pH = –log(1.0 × 10⁻¹²) = 12.
9. D – pH change of 3 means 10³ = 1000 times change in [H⁺].
10. A – pOH = 9 → pH = 14 – 9 = 5.
11. B – Neutral solution pH = 7 at 25°C.
12. C – pH + pOH = 14 at 25°C.
13. C – pOH = 3 → pH = 14 – 3 = 11.
14. A – 0.01 M HCl fully dissociates → pH = 2.
15. E – pH 9 is basic; [H⁺] = 10⁻⁹ M.
16. C – pH = 5 → [H⁺] = 10⁻⁵ M.
17. A – pH = –log(3.2 × 10⁻⁴) ≈ 3.49.
18. C – pH = 11 → pOH = 3 → [OH⁻] = 10⁻³ M.
19. D – Ammonia is basic with pH ~11, highest among options.
20. C – pH = –log(5.0 × 10⁻⁵) ≈ 4.3.
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