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.
CSS - PMS - CCE - PCS - General Science
Acid/Base
The main acid in vinegar is:
A. Acetic acid
B. Citric acid
C. Lactic acid
D. Sulfuric acid
Correct Answer: A
A: Correct because vinegar is a dilute aqueous solution containing acetic acid. B: Incorrect because citric acid is common in citrus fruits. C: Incorrect because lactic acid is associated with sour milk and muscles. D: Incorrect because sulfuric acid is a strong mineral acid not used as the main acid in vinegar.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Baking soda has the chemical formula:
A. Na₂CO₃
B. NaHCO₃
C. NaOH
D. K₂CO₃
Correct Answer: B
A: Incorrect because Na₂CO₃ is sodium carbonate or soda ash. B: Correct because baking soda is sodium hydrogen carbonate, NaHCO₃. C: Incorrect because NaOH is caustic soda. D: Incorrect because K₂CO₃ is potassium carbonate.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Tooth enamel begins to dissolve significantly when mouth pH falls below about:
A. 9.5
B. 7.5
C. 5.5
D. 13
Correct Answer: C
A: Incorrect because 9.5 is basic. B: Incorrect because 7.5 is slightly basic. C: Correct because tooth enamel demineralization increases when plaque pH falls below roughly 5.5. D: Incorrect because 13.0 is strongly basic.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Antacids relieve acidity mainly by:
A. Neutralizing excess stomach acid
B. Producing more HCl
C. Stopping all digestion permanently
D. Increasing carbon dioxide in blood
Correct Answer: A
A: Correct because antacids contain mild bases that neutralize excess gastric acid. B: Incorrect because producing more HCl would worsen acidity. C: Incorrect because they do not permanently stop all digestion. D: Incorrect because raising blood carbon dioxide is not their intended action.
CSS - PMS - CCE - PCS - General Science
Acid/Base
The main acid present in the human stomach is:
A. Hydrochloric acid
B. Sulfuric acid
C. Acetic acid
D. Nitric acid
Correct Answer: A
A: Correct because gastric juice contains hydrochloric acid, which aids digestion and helps kill microbes. B: Incorrect because sulfuric acid is not a normal stomach acid. C: Incorrect because acetic acid is the main acid in vinegar. D: Incorrect because nitric acid is not normally secreted in the stomach.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Acid rain is mainly associated with atmospheric oxides of:
A. Sulfur and nitrogen
B. Sodium and potassium
C. Calcium and magnesium
D. Helium and neon
Correct Answer: A
A: Correct because sulfur oxides and nitrogen oxides form acids in the atmosphere and contribute to acid rain. B: Incorrect because sodium and potassium oxides are not the main atmospheric cause. C: Incorrect because calcium and magnesium compounds can help neutralize acidity. D: Incorrect because helium and neon are noble gases and do not form acid-rain oxides under normal conditions.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Which hydroxide is amphoteric?
A. NaOH
B. KOH
C. Al(OH)₃
D. Ba(OH)₂
Correct Answer: C
A: Incorrect because NaOH is a strong base. B: Incorrect because KOH is a strong base. C: Correct because Al(OH)₃ can react with both acids and strong bases. D: Incorrect because Ba(OH)₂ is a strong base when dissolved.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Which oxide is amphoteric?
A. Al₂O₃
B. SO₃
C. K₂O
D. CO₂
Correct Answer: A
A: Correct because Al₂O₃ reacts with both acids and strong bases, so it is amphoteric. B: Incorrect because SO₃ is acidic. C: Incorrect because K₂O is basic. D: Incorrect because CO₂ is acidic.