1. pH is defined as:
A) log [H⁺]
B) –log [H⁺]
C) log [OH⁻]
D) –log [OH⁻]
Answer: B
Explanation: pH = –log₁₀[H⁺], where [H⁺] is the hydrogen ion concentration in mol/L.
2. The pH of a neutral solution at 25 °C is:
A) 0
B) 7
C) 14
D) 1
Answer: B
Explanation: At 25 °C, pure water has [H⁺] = 1 × 10⁻⁷ → pH = 7.
3. The pH of 0.001 M HCl solution is:
A) 1
B) 2
C) 3
D) 4
Answer: C
Explanation: pH = –log [H⁺] = –log (10⁻³) = 3.
4. Which solution has the lowest pH?
A) 0.01 M HCl
B) 0.001 M HCl
C) Pure water
D) 0.01 M NaOH
Answer: A
Explanation: Higher [H⁺] → lower pH. 0.01 M HCl has pH = 2, the lowest here.
5. The pH of 0.01 M NaOH solution is:
A) 12
B) 10
C) 2
D) 4
Answer: A
Explanation: [OH⁻] = 0.01 = 10⁻² → pOH = 2 → pH = 14 – 2 = 12.
6. What is the pOH of a neutral solution at 25 °C?
A) 0
B) 7
C) 14
D) 1
Answer: B
Explanation: For neutral water, [OH⁻] = 10⁻⁷ → pOH = 7.
7. Which formula relates pH and pOH?
A) pH + pOH = 0
B) pH + pOH = 7
C) pH + pOH = 10
D) pH + pOH = 14
Answer: D
Explanation: At 25 °C, pH + pOH = 14 (since Kw = 10⁻¹⁴).
8. The solution with pH = 1 is:
A) Strongly acidic
B) Weakly acidic
C) Neutral
D) Basic
Answer: A
Explanation: pH < 7 → acidic. Very low pH (1) → strongly acidic.
9. The solution with pH = 9 is:
1A) Strongly acidic
B) Weakly acidic
C) Weakly basic
D) Strongly basic
Answer: C
Explanation: pH > 7 → basic. Since it’s near 7, it’s weakly basic.
10. The pH of a strong acid increases when:
A) Diluted with water
B) Heated
C) Mixed with strong base
D) Both A and C
Answer: D
Explanation: Dilution reduces [H⁺], neutralization with base consumes H⁺ → pH increases.
11. Which indicator is used to measure pH around 7?
A) Phenolphthalein
B) Methyl orange
C) Bromothymol blue
D) Litmus
Answer: C
Explanation: Bromothymol blue has transition range 6.0–7.6 → suitable near neutral pH.
12. Which indicator is suitable for strong acid vs strong base titration?
A) Phenolphthalein
B) Methyl orange
C) Either A or B
D) None
Answer: C
Explanation: Strong acid–strong base equivalence point at pH ≈ 7 → either phenolphthalein or methyl orange can work.
13. pH paper turns red in:
A) Acidic solution
B) Basic solution
C) Neutral solution
D) Salt solution
Answer: A
Explanation: Acids turn pH paper red.
14. The pH of gastric juice is about:
A) 7
B) 1–2
C) 4–5
D) 9
Answer: B
Explanation: Gastric juice contains HCl, pH ≈ 1–2.
15. The pH of human blood is about:
A) 4.5
B) 6.0
C) 7.4
D) 9.0
Answer: C
Explanation: Normal blood pH ≈ 7.35–7.45.
16. The pH of saliva after meals is usually:
A) 2
B) 4
C) 6.5–7.5
D) 9
Answer: C
Explanation: Saliva is slightly acidic to neutral (6.5–7.5).
17. If [H⁺] = 1 × 10⁻⁵ M, the pH is:
A) 3
B) 5
C) 7
D) 9
Answer: B
Explanation: pH = –log (10⁻⁵) = 5.
18. If pH = 11, then [OH⁻] is:
A) 10⁻³ M
B) 10⁻² M
C) 10⁻¹¹ M
D) 10⁻¹ M
Answer: A
Explanation: pOH = 14 – 11 = 3 → [OH⁻] = 10⁻³ M.
19. The ionic product of water (Kw) at 25 °C is:
A) 1 × 10⁻⁷
B) 1 × 10⁻¹⁰
C) 1 × 10⁻¹⁴
D) 1 × 10⁻¹⁶
Answer: C
Explanation: Kw = [H⁺][OH⁻] = 1 × 10⁻¹⁴ at 25 °C.
20. When pH = 7 at 25 °C, then:
A) Solution is neutral
B) [H⁺] = [OH⁻]
C) [H⁺] = 10⁻⁷
D) All of the above
Answer: D
Explanation: Neutral solution has pH = 7, [H⁺] = [OH⁻] = 10⁻⁷.
21. Which solution will have pH > 7?
A) 0.1 M HCl
B) Pure water
C) 0.1 M NaOH
D) H₂SO₄
Answer: C
Explanation: NaOH is a strong base → pH > 7.
22. If pH of solution decreases from 5 to 3, then [H⁺]:
A) Doubles
B) Increases by 100 times
C) Decreases by 10 times
D) Remains constant
Answer: B
Explanation: pH drop by 2 units → [H⁺] increases by 10² = 100 times.
23. Which of the following is a weak acid?
A) HCl
B) HNO₃
C) CH₃COOH
D) H₂SO₄
Answer: C
Explanation: Acetic acid (CH₃COOH) is weak, partially ionized.
24. The pH scale usually ranges from:
A) 0 to 7
B) –1 to 1
C) 0 to 14
D) 1 to 14
Answer: C
Explanation: Normal pH scale = 0–14, but can go below 0 or above 14 in extreme cases.
25. Which device is used to measure pH accurately?
A) Voltmeter
B) pH meter
C) Ammeter
D) Galvanometer
Answer: B
Explanation: A pH meter (glass electrode) measures pH accurately.
26. The pH of 0.1 M HCl solution is:
A) 0
B) 1
C) 2
D) 3
Answer: B
Explanation: pH = –log [H⁺] = –log (0.1) = 1.
27. The pH of 0.001 M NaOH solution is:
A) 11
B) 12
C) 13
D) 3
Answer: A
Explanation: [OH⁻] = 10⁻³ → pOH = 3 → pH = 14 – 3 = 11.
28. A solution has [H⁺] = 1 × 10⁻⁹ M. Its pH is:
A) 9
B) 7
C) 5
D) 11
Answer: A
Explanation: pH = –log [H⁺] = –log (10⁻⁹) = 9.
29. The pH of 1 × 10⁻⁴ M HCl solution is:
A) 2
B) 3
C) 4
D) 5
Answer: C
Explanation: pH = –log (10⁻⁴) = 4.
30. A solution with pH = 13 has [OH⁻] = ?
A) 10⁻¹
B) 10⁻²
C) 10⁻¹³
D) 10⁻⁷
Answer: A
Explanation: pOH = 14 – 13 = 1 → [OH⁻] = 10⁻¹ M.
31. Which salt solution has pH = 7?
A) NaCl
B) NH₄Cl
C) CH₃COONa
D) Na₂CO₃
Answer: A
Explanation: NaCl is formed from strong acid (HCl) and strong base (NaOH) → neutral solution.
32. Which salt solution is acidic?
A) NaCl
B) NH₄Cl
C) Na₂CO₃
D) CH₃COONa
Answer: B
Explanation: NH₄Cl (from strong acid + weak base) hydrolyzes to give acidic solution.
33. Which salt solution is basic?
A) KCl
B) CH₃COONa
C) NH₄Cl
D) NaNO₃
Answer: B
Explanation: Sodium acetate (from strong base + weak acid) gives basic solution.
34. A buffer solution is one which:
A) Changes pH sharply with acid addition
B) Maintains nearly constant pH
C) Is neutral always
D) Has pH = 14
Answer: B
Explanation: Buffers resist change in pH upon addition of small amounts of acid/base.
35. Which is an example of acidic buffer?
A) NH₄Cl + NH₄OH
B) CH₃COOH + CH₃COONa
C) H₂SO₄ + Na₂SO₄
D) NaOH + NaCl
Answer: B
Explanation: Acidic buffer = weak acid + its salt (e.g., CH₃COOH + CH₃COONa).
36. Which is an example of basic buffer?
A) HCl + NaCl
B) CH₃COOH + CH₃COONa
C) NH₄OH + NH₄Cl
D) H₂SO₄ + Na₂SO₄
Answer: C
Explanation: Basic buffer = weak base + its salt (e.g., NH₄OH + NH₄Cl).
37. The Henderson–Hasselbalch equation is used for:
A) Determining Kw
B) Calculating pH of buffer
C) Measuring solubility
D) Determining ΔG
Answer: B
Explanation: Henderson–Hasselbalch equation:
pH = pKa + log([salt]/[acid]).
38. The pH of buffer solution made of 0.1 M CH₃COOH and 0.1 M CH₃COONa (Ka = 1.8 × 10⁻⁵) is:
A) 4.74
B) 7
C) 3
D) 5.5
Answer: A
Explanation: pH = pKa + log([salt]/[acid]) = 4.74 + log(1) = 4.74.
39. In buffer solutions, maximum buffer capacity is when:
A) [salt] > [acid]
B) [acid] > [salt]
C) [salt] = [acid]
D) pKa = 0
Answer: C
Explanation: Buffer is most effective when [acid] = [salt] → pH = pKa.
40. The pH of blood is maintained by:
A) HCl buffer
B) CH₃COOH buffer
C) H₂CO₃/HCO₃⁻ buffer
D) NH₄Cl buffer
Answer: C
Explanation: Blood pH ≈ 7.4 is regulated by carbonic acid/bicarbonate buffer.
41. Which of the following can act as a buffer system?
A) HNO₃ + NaNO₃
B) HCl + NaCl
C) CH₃COOH + CH₃COONa
D) NaOH + KOH
Answer: C
Explanation: Buffer = weak acid + its salt.
42. When a small amount of acid is added to a buffer:
A) pH decreases sharply
B) pH increases sharply
C) pH remains nearly constant
D) pH becomes neutral
Answer: C
Explanation: Buffer resists pH change.
43. Which salt solution is alkaline due to hydrolysis?
A) KNO₃
B) Na₂CO₃
C) NaCl
D) NH₄Cl
Answer: B
Explanation: Na₂CO₃ undergoes hydrolysis → basic solution.
44. Which salt solution is acidic due to hydrolysis?
A) NaCl
B) KNO₃
C) NH₄Cl
D) Na₂CO₃
Answer: C
Explanation: NH₄Cl hydrolyzes → acidic solution.
45. Which of the following has pH > 7?
A) HCl
B) NH₄Cl
C) Na₂CO₃
D) CH₃COOH
Answer: C
Explanation: Sodium carbonate solution is basic.
46. The pH of 0.01 M NaOH solution at 25 °C is:
A) 12
B) 2
C) 7
D) 10
Answer: A
Explanation: [OH⁻] = 10⁻² → pOH = 2 → pH = 12.
47. Which solution has highest [H⁺]?
A) pH = 1
B) pH = 3
C) pH = 5
D) pH = 7
Answer: A
Explanation: Lower pH → higher [H⁺].
48. The pH of a solution is 6. The solution is:
A) Strongly acidic
B) Weakly acidic
C) Neutral
D) Weakly basic
Answer: B
Explanation: pH slightly below 7 → weak acid.
49. A solution with pH = 8 has [H⁺] = ?
A) 10⁻⁶
B) 10⁻⁸
C) 10⁻¹⁴
D) 10⁻²
Answer: B
Explanation: pH = –log [H⁺] → [H⁺] = 10⁻⁸.
50. The pH of a buffer is equal to pKa of the acid when:
A) [salt] = [acid]
B) [salt] > [acid]
C) [acid] > [salt]
D) Acid is strong
Answer: A
Explanation: From Henderson–Hasselbalch equation:
pH = pKa + log(1) = pKa.
51. The pH of lemon juice is about:
A) 2
B) 5
C) 7
D) 9
Answer: A
Explanation: Lemon juice is strongly acidic (citric acid), pH ≈ 2.
52. The pH of milk is about:
A) 3.5
B) 6.5
C) 7.0
D) 8.5
Answer: B
Explanation: Fresh milk has slightly acidic pH ≈ 6.5.
53. The pH of soap solution is usually:
A) <7
B) =7
C) >7
D) Exactly 14
Answer: C
Explanation: Soap solution is basic, hence pH > 7.
54. Tooth decay occurs when mouth pH falls below:
A) 7.0
B) 6.0
C) 5.5
D) 9.0
Answer: C
Explanation: Below pH 5.5, enamel dissolves due to acid produced by bacteria.
55. The pH of seawater is about:
A) 5
B) 7
C) 8.2
D) 10
Answer: C
Explanation: Seawater is slightly alkaline, pH ≈ 8.2.
56. Rainwater is naturally acidic due to:
A) HNO₃
B) H₂SO₄
C) CO₂
D) NH₃
Answer: C
Explanation: CO₂ dissolves in rainwater forming carbonic acid → natural pH ≈ 5.6.
57. Acid rain has pH value:
A) >7
B) <5.6
C) Exactly 7
D) >10
Answer: B
Explanation: Acid rain occurs when pH < 5.6 (due to SO₂, NOx).
58. The pH of human urine typically ranges between:
A) 1–2
B) 3–4
C) 6–7
D) 10–11
Answer: C
Explanation: Urine is slightly acidic to neutral (≈ 6.0–7.0).
59. The optimum pH of pepsin enzyme is:
A) 1–2
B) 4–5
C) 7
D) 9
Answer: A
Explanation: Pepsin works best in acidic gastric juice (pH 1–2).
60. The optimum pH of trypsin enzyme is:
A) 2
B) 5
C) 7–8
D) 10
Answer: C
Explanation: Trypsin acts in the intestine at alkaline pH (≈ 7–8).
61. The pH of blood is maintained close to 7.4 by:
A) HCl buffer
B) CH₃COOH buffer
C) H₂CO₃/HCO₃⁻ buffer
D) NaOH buffer
Answer: C
Explanation: The carbonic acid–bicarbonate buffer controls blood pH.
62. A drop in blood pH below 7.35 is called:
A) Alkalosis
B) Acidosis
C) Neutralization
D) Buffering
Answer: B
Explanation: Blood pH <7.35 → acidosis (too acidic).
63. A rise in blood pH above 7.45 is called:
A) Alkalosis
B) Acidosis
C) Neutralization
D) Hydrolysis
Answer: A
Explanation: Blood pH >7.45 → alkalosis (too basic).
64. Which organ regulates blood pH along with buffers?
A) Heart
B) Kidney
C) Stomach
D) Liver
Answer: B
Explanation: Kidneys regulate pH by excreting H⁺ and reabsorbing HCO₃⁻.
65. Which environmental problem is directly related to low pH of rain?
A) Greenhouse effect
B) Ozone hole
C) Acid rain
D) Eutrophication
Answer: C
Explanation: Acid rain is precipitation with low pH (<5.6).
66. The pH of strong black coffee is about:
A) 2.0
B) 4.5–5.0
C) 7.0
D) 9.0
Answer: B
Explanation: Coffee is mildly acidic, pH ≈ 4.5–5.0.
67. The pH of bleach (NaOCl solution) is usually:
A) 2
B) 5
C) 7
D) 12–13
Answer: D
Explanation: Bleach is strongly alkaline, pH 12–13.
68. The logarithmic nature of pH scale means that a pH change of 1 unit corresponds to:
A) 2-fold change in [H⁺]
B) 5-fold change in [H⁺]
C) 10-fold change in [H⁺]
D) 100-fold change in [H⁺]
Answer: C
Explanation: One pH unit change = 10× change in hydrogen ion concentration.
69. The pH of tomato juice is about:
A) 2.0
B) 4.2
C) 6.0
D) 7.5
Answer: B
Explanation: Tomato juice is moderately acidic, pH ≈ 4.2.
70. The pH of baking soda solution is around:
A) 3
B) 7
C) 8–9
D) 12
Answer: C
Explanation: Baking soda (NaHCO₃) is weakly basic, pH ≈ 8–9.
71. If a solution has [H⁺] = 2 × 10⁻³ M, its pH is:
A) 2.7
B) 3.0
C) 5.0
D) 11.3
Answer: A
Explanation: pH = –log (2 × 10⁻³) ≈ 2.7.
72. If a solution has pOH = 5, then its pH = ?
A) 5
B) 7
C) 9
D) 14
Answer: C
Explanation: pH + pOH = 14 → pH = 14 – 5 = 9.
73. A solution has [OH⁻] = 1 × 10⁻⁵ M. Its pH is:
A) 5
B) 7
C) 9
D) 11
Answer: C
Explanation: pOH = 5 → pH = 14 – 5 = 9.
74. The pH of vinegar is about:
A) 2–3
B) 5–6
C) 7
D) 9–10
Answer: A
Explanation: Vinegar contains acetic acid, pH ≈ 2–3.
75. The pH of orange juice is approximately:
A) 2.0
B) 3.5–4.0
C) 7.0
D) 9.0
Answer: B
Explanation: Orange juice is acidic (citric acid), pH ≈ 3.5–4.0.
76. If pH of a solution is 2, the [H⁺] concentration is:
A) 1 × 10⁻² M
B) 1 × 10⁻³ M
C) 1 × 10⁻⁴ M
D) 1 × 10⁻⁶ M
Answer: A
Explanation: pH = –log[H⁺] → [H⁺] = 10⁻² M.
77. The pH of a solution increases by 1 unit. This means the [H⁺] concentration:
A) Doubled
B) Increased 10×
C) Decreased 10×
D) Remained constant
Answer: C
Explanation: 1 pH unit rise = 10-fold decrease in [H⁺].
78. If pH of a solution is 10, then [OH⁻] = ?
A) 10⁻¹⁰ M
B) 10⁻⁴ M
C) 10⁻⁵ M
D) 10⁻³ M
Answer: B
Explanation: pH = 10 → pOH = 4 → [OH⁻] = 10⁻⁴ M.
79. The pH of 0.01 M H₂SO₄ solution is approximately:
A) 1
B) 2
C) 12
D) 14
Answer: A
Explanation: Strong diprotic acid: [H⁺] ≈ 2 × 0.01 = 0.02 → pH ≈ 1.7 (approximate to 1).
80. Which of the following is used in industries to control pH?
A) Buffers
B) Litmus paper
C) Distilled water
D) Phenolphthalein
Answer: A
Explanation: Buffer solutions are used in fermentation, pharmaceuticals, etc., to control pH.
81. In soil chemistry, crop yield depends strongly on:
A) Soil temperature
B) Soil pH
C) Soil pressure
D) Soil density
Answer: B
Explanation: Soil pH affects availability of nutrients to plants.
82. The ideal pH range for most crops is:
A) 2–3
B) 5.5–7.5
C) 8–9
D) 10–12
Answer: B
Explanation: Most crops grow best in slightly acidic to neutral soils.
83. In swimming pools, the pH of water is maintained around:
A) 4–5
B) 6–7
C) 7.2–7.8
D) 9–10
Answer: C
Explanation: Pool water is kept slightly basic to prevent irritation and control bacteria.
84. The pH of shampoo is usually kept around:
A) 2
B) 4–6
C) 7
D) 10
Answer: B
Explanation: Shampoos are mildly acidic (pH 4–6) to match scalp and maintain hair health.
85. The pH of detergents is usually:
A) Neutral
B) Slightly acidic
C) Basic
D) Zero
Answer: C
Explanation: Most detergents are alkaline to remove grease.
86. The pH of lime water (Ca(OH)₂ solution) is about:
A) 2
B) 7
C) 12
D) 14
Answer: C
Explanation: Lime water is a strong base, pH ≈ 12.
87. A buffer solution is best when:
A) [Salt] >> [Acid]
B) [Acid] >> [Salt]
C) [Salt] = [Acid]
D) Neither acid nor salt is present
Answer: C
Explanation: Buffer capacity is maximum when [acid] = [salt].
88. Which food preservative works best in acidic medium (low pH)?
A) Sodium chloride
B) Benzoic acid
C) Sugar
D) Baking soda
Answer: B
Explanation: Benzoic acid acts effectively as preservative at low pH.
89. Which disease in humans is related to very low gastric pH?
A) Acidity/Ulcer
B) Diabetes
C) Hypertension
D) Tuberculosis
Answer: A
Explanation: Excess gastric acid (pH ~1) leads to acidity and ulcers.
90. The pH of soap solution is generally:
A) 4
B) 6
C) 8–9
D) 12
Answer: C
Explanation: Soap solution is weakly basic, pH 8–9.
91. The pH of lime juice is:
A) 2
B) 4
C) 7
D) 10
Answer: A
Explanation: Lime juice is strongly acidic, pH ≈ 2.
92. Which instrument measures pH accurately?
A) Ammeter
B) pH meter
C) Thermometer
D) Hygrometer
Answer: B
Explanation: A pH meter with glass electrode measures pH precisely.
93. The pH of strong NaOH solution is close to:
A) 0
B) 7
C) 14
D) 1
Answer: C
Explanation: Concentrated NaOH solution is highly basic, pH ≈ 14.
94. The pH of saliva in the morning (before eating) is generally:
A) 4–5
B) 6.5–7.5
C) 8–9
D) 10
Answer: B
Explanation: Saliva is near neutral in the morning, pH ≈ 6.5–7.5.
95. If a solution has [H⁺] = 1 × 10⁻¹² M, its pH is:
A) 2
B) 7
C) 10
D) 12
Answer: D
Explanation: pH = –log (10⁻¹²) = 12.
96. The pH of cola drinks is about:
A) 1
B) 2.5
C) 7
D) 10
Answer: B
Explanation: Cola drinks are acidic due to carbonic and phosphoric acid, pH ≈ 2.5.
97. Which chemical is used to neutralize acidic soils?
A) NaCl
B) NaOH
C) CaCO₃
D) H₂SO₄
Answer: C
Explanation: Lime (CaCO₃) is used to raise soil pH (neutralize acidity).
98. Which chemical is added to swimming pools to maintain pH?
A) HCl
B) Na₂CO₃
C) H₂SO₄
D) CH₃COOH
Answer: B
Explanation: Sodium carbonate (soda ash) is added to keep pool water alkaline.
99. At 25 °C, if pH = 6, then pOH = ?
A) 6
B) 7
C) 8
D) 14
Answer: C
Explanation: pOH = 14 – pH = 14 – 6 = 8.
100. Which of the following statements about pH is correct?
A) pH changes linearly with [H⁺]
B) pH is logarithmic measure of [H⁺]
C) Neutral solutions always have pH = 7 at any temperature
D) pH cannot be less than 0
Answer: B
Explanation: pH is logarithmic scale of [H⁺]. At higher temperatures, neutral pH < 7, and very concentrated acids can have pH < 0.