CSS - PMS - CCE - PCS - General Science
Acid/Base
A buffer solution is one that:
A. Resists sudden changes in pH
B. Always has pH 7
C. Contains only a strong acid
D. Cannot contain water
Correct Answer: A
A: Correct because a buffer minimizes pH change when small amounts of acid or base are added. B: Incorrect because buffers may be acidic or basic, not always neutral. C: Incorrect because a strong acid alone does not make an effective buffer. D: Incorrect because buffers are usually aqueous solutions.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Which species can act as both a Brønsted acid and a Brønsted base?
A. HSO₄⁻
B. Na⁺
C. Cl⁻ only in water
D. CH₄
Correct Answer: A
A: Correct because HSO₄⁻ can donate H⁺ to form SO₄²⁻ or accept H⁺ to form H₂SO₄. B: Incorrect because Na⁺ has no proton to donate and is not a typical proton acceptor. C: Incorrect because Cl⁻ can accept a proton but cannot donate one. D: Incorrect because CH₄ is not normally amphiprotic in aqueous acid–base chemistry.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Water is described as amphiprotic because it can:
A. Only donate protons
B. Only accept protons
C. Both donate and accept protons
D. Neither donate nor accept protons
Correct Answer: C
A: Incorrect because water is not limited to proton donation. B: Incorrect because water is not limited to proton acceptance. C: Correct because water can donate H⁺ to form OH⁻ or accept H⁺ to form H₃O⁺. D: Incorrect because water clearly participates in proton-transfer reactions.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Which pair is a conjugate acid–base pair?
A. HCl and Cl⁻
B. HCl and NaOH
C. NaCl and KCl
D. H₂SO₄ and HNO₃
Correct Answer: A
A: Correct because HCl and Cl⁻ differ by exactly one proton. B: Incorrect because HCl and NaOH are an acid and base but not a conjugate pair. C: Incorrect because NaCl and KCl are different salts. D: Incorrect because H₂SO₄ and HNO₃ are two different acids and do not differ by one proton.
CSS - PMS - CCE - PCS - General Science
Acid/Base
The conjugate acid of NH₃ is:
A. NH₂⁻
B. NH₄⁺
C. N₂H₄
D. NO₃⁻
Correct Answer: B
A: Incorrect because NH₂⁻ forms by proton loss. B: Correct because NH₃ accepts one proton to form NH₄⁺. C: Incorrect because N₂H₄ is hydrazine, not the conjugate acid. D: Incorrect because NO₃⁻ is nitrate and is unrelated.
CSS - PMS - CCE - PCS - General Science
Acid/Base
The conjugate base of H₂CO₃ is:
A. H₃CO₃⁺
B. HCO₃⁻
C. CO₃²⁻ directly after one proton loss
D. OH⁻
Correct Answer: B
A: Incorrect because H₃CO₃⁺ would result from proton gain. B: Correct because loss of one proton from H₂CO₃ produces HCO₃⁻. C: Incorrect because CO₃²⁻ forms after loss of two protons overall, not one. D: Incorrect because OH⁻ is not formed by simply removing one proton from H₂CO₃.
CSS - PMS - CCE - PCS - General Science
Acid/Base
In pure water at 25°C, the concentration of H⁺ is approximately:
A. 1 × 10⁻¹ M
B. 1 × 10⁻⁷ M
C. 1 × 10⁻¹⁴ M
D. 7 M
Correct Answer: B
A: Incorrect because 10⁻¹ M would be strongly acidic. B: Correct because in neutral pure water, [H⁺] = [OH⁻] ≈ 1 × 10⁻⁷ M. C: Incorrect because 10⁻¹⁴ M is Kw, not the individual ion concentration. D: Incorrect because 7 is a pH value, not a molar concentration.
CSS - PMS - CCE - PCS - General Science
Acid/Base
The ionic product of water, Kw, at 25°C is approximately:
A. 1 × 10⁻⁷
B. 1 × 10⁻¹⁴
C. 14
D. 7
Correct Answer: B
A: Incorrect because 10⁻⁷ is the concentration of each ion in neutral water. B: Correct because Kw = [H⁺][OH⁻] is approximately 1.0 × 10⁻¹⁴ at 25°C. C: Incorrect because 14 is pKw, not Kw. D: Incorrect because 7 is the neutral pH at 25°C, not Kw.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Compared with a solution of pH 5, a solution of pH 3 has how many times greater hydrogen-ion concentration?
A. 2 times
B. 10 times
C. 100 times
D. 1000 times
Correct Answer: C
A: Incorrect because pH is logarithmic, so the factor is not simply 2. B: Incorrect because 10 times corresponds to one pH unit. C: Correct because a difference of two pH units corresponds to 10², or 100 times, difference in [H⁺]. D: Incorrect because 1000 times corresponds to three pH units.
CSS - PMS - CCE - PCS - General Science
Acid/Base
If the hydrogen-ion concentration increases tenfold, the pH generally:
A. Increases by 10
B. Decreases by 1
C. Remains unchanged
D. Becomes exactly 7
Correct Answer: B
A: Incorrect because pH does not increase linearly with concentration. B: Correct because because pH is logarithmic, a tenfold increase in [H⁺] lowers pH by one unit. C: Incorrect because a concentration change alters pH. D: Incorrect because the solution does not necessarily become neutral.
CSS - PMS - CCE - PCS - General Science
Acid/Base
What is the pH of 1.0 × 10⁻² M NaOH at 25°C, assuming complete dissociation?
A. 2
B. 7
C. 10
D. 12
Correct Answer: D
A: Incorrect because 2 is the pOH, not the pH. B: Incorrect because 7 is neutral. C: Incorrect because 10 would correspond to pOH 4. D: Correct because [OH⁻] = 10⁻² M gives pOH 2, and pH = 14 − 2 = 12.
CSS - PMS - CCE - PCS - General Science
Acid/Base
What is the pH of 1.0 × 10⁻³ M HCl, assuming complete ionization?
A. 1
B. 2
C. 3
D. 11
Correct Answer: C
A: Incorrect because pH 1 corresponds to 10⁻¹ M H⁺. B: Incorrect because pH 2 corresponds to 10⁻² M H⁺. C: Correct because for strong monoprotic HCl, [H⁺] = 10⁻³ M, so pH = 3. D: Incorrect because pH 11 is basic and cannot describe this HCl solution.
CSS - PMS - CCE - PCS - General Science
Acid/Base
At 25°C, the relationship between pH and pOH is:
A. pH × pOH = 14
B. pH + pOH = 14
C. pH − pOH = 7 always
D. pH = pOH for every solution
Correct Answer: B
A: Incorrect because the relationship is additive, not multiplicative. B: Correct because at 25°C, pH + pOH equals pKw, approximately 14. C: Incorrect because the difference is not always 7. D: Incorrect because pH equals pOH only for a neutral solution at that temperature.
CSS - PMS - CCE - PCS - General Science
Acid/Base
The mathematical definition of pOH is:
A. pOH = −log[OH⁻]
B. pOH = log[H⁺]
C. pOH = [OH⁻] + 7
D. pOH = 14 × [OH⁻]
Correct Answer: A
A: Correct because pOH is the negative base-10 logarithm of hydroxide-ion concentration or activity. B: Incorrect because log[H⁺] relates incorrectly to pH and lacks the negative sign. C: Incorrect because adding 7 is not the definition. D: Incorrect because multiplication by 14 is not the pOH equation.
CSS - PMS - CCE - PCS - General Science
Acid/Base
The mathematical definition of pH is:
A. pH = log[H⁺]
B. pH = −log[H⁺]
C. pH = [H⁺] × 10
D. pH = 14 + [H⁺]
Correct Answer: B
A: Incorrect because the negative sign is required. B: Correct because pH is defined as the negative base-10 logarithm of hydrogen-ion activity, commonly approximated by concentration. C: Incorrect because multiplying concentration by 10 does not define pH. D: Incorrect because adding hydrogen concentration to 14 is not the pH equation.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Which instrument or material is commonly used for a quick approximate pH test?
A. pH paper
B. Thermometer
C. Ammeter
D. Barometer
Correct Answer: A
A: Correct because pH paper changes color according to the acidity or basicity of a solution. B: Incorrect because a thermometer measures temperature. C: Incorrect because an ammeter measures electric current. D: Incorrect because a barometer measures atmospheric pressure.
CSS - PMS - CCE - PCS - General Science
Acid/Base
The electrolyte commonly used in a lead–acid car battery is:
A. Dilute sulfuric acid
B. Concentrated acetic acid
C. Sodium hydroxide
D. Pure water only
Correct Answer: A
A: Correct because lead–acid batteries use dilute sulfuric acid as the electrolyte. B: Incorrect because acetic acid is not the standard electrolyte. C: Incorrect because sodium hydroxide is used in some alkaline battery systems, not lead–acid batteries. D: Incorrect because pure water alone cannot provide the required ionic medium.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Tamarind is commonly associated with which acid?
A. Tartaric acid
B. Hydrochloric acid
C. Sulfurous acid
D. Perchloric acid
Correct Answer: A
A: Correct because tamarind contains tartaric acid, which contributes to its sour taste. B: Incorrect because hydrochloric acid is not a food acid in tamarind. C: Incorrect because sulfurous acid is not its characteristic acid. D: Incorrect because perchloric acid is a strong laboratory acid, not a tamarind acid.
CSS - PMS - CCE - PCS - General Science
Acid/Base
The acid commonly associated with sour milk or curd is:
A. Lactic acid
B. Nitric acid
C. Carbonic acid
D. Hydrofluoric acid
Correct Answer: A
A: Correct because lactic acid is produced during fermentation of lactose by bacteria. B: Incorrect because nitric acid is a strong mineral acid. C: Incorrect because carbonic acid forms from dissolved carbon dioxide. D: Incorrect because hydrofluoric acid is not produced in curd formation.
CSS - PMS - CCE - PCS - General Science
Acid/Base
The characteristic acid in lemons and many citrus fruits is:
A. Citric acid
B. Hydrochloric acid
C. Sulfuric acid
D. Boric acid
Correct Answer: A
A: Correct because citric acid gives many citrus fruits their sour taste. B: Incorrect because hydrochloric acid is found in gastric juice. C: Incorrect because sulfuric acid is a mineral acid. D: Incorrect because boric acid is not the main acid in citrus fruit.