CSS - PMS - CCE - PCS - General Science
Acid/Base
A standard solution is a solution whose:
A. Concentration is accurately known
B. Color is always blue
C. pH is always 7
D. Volume is always one litre
Correct Answer: A
A: Correct because a standard solution has a precisely known concentration. B: Incorrect because standard solutions can have many colors. C: Incorrect because they may be acidic, basic, or neutral. D: Incorrect because their prepared volume need not always be one litre.
CSS - PMS - CCE - PCS - General Science
Acid/Base
During a typical titration, the analyte is commonly placed in a:
A. Conical flask
B. Burette tip cap
C. Watch glass
D. Gas jar
Correct Answer: A
A: Correct because a conical flask allows swirling without excessive splashing. B: Incorrect because the burette holds titrant, not normally the analyte. C: Incorrect because a watch glass is unsuitable for titration mixing. D: Incorrect because a gas jar is intended for gases.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Which apparatus is commonly used to transfer a fixed accurate volume of analyte?
A. Volumetric pipette
B. Measuring cylinder only
C. Evaporating dish
D. Funnel
Correct Answer: A
A: Correct because a volumetric pipette is calibrated to deliver one fixed volume accurately. B: Incorrect because a measuring cylinder is less precise. C: Incorrect because an evaporating dish is used for heating and evaporation. D: Incorrect because a funnel assists transfer or filtration but does not measure a fixed accurate volume.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Which apparatus is used to deliver a measured, variable volume during titration?
A. Burette
B. Beaker
C. Test tube
D. Watch glass
Correct Answer: A
A: Correct because a burette has fine graduations and a stopcock for controlled delivery of variable volume. B: Incorrect because a beaker is not sufficiently accurate for titration delivery. C: Incorrect because a test tube is not calibrated for precise volume delivery. D: Incorrect because a watch glass is not a volumetric instrument.
CSS - PMS - CCE - PCS - General Science
Acid/Base
The equivalence point in a titration is reached when:
A. Acid and base have reacted in stoichiometric proportions
B. The solution first begins to boil
C. The indicator is added
D. The burette is completely empty
Correct Answer: A
A: Correct because the reacting acid and base are present in chemically equivalent stoichiometric amounts. B: Incorrect because boiling is unrelated to equivalence. C: Incorrect because adding indicator does not itself establish equivalence. D: Incorrect because a burette need not be emptied.
CSS - PMS - CCE - PCS - General Science
Acid/Base
In an acid–base titration, the endpoint is usually detected by:
A. A color change of a suitable indicator
B. Boiling the solution dry
C. Measuring mass only
D. Adding a metal strip
Correct Answer: A
A: Correct because a suitable indicator changes color near the equivalence region and signals the endpoint. B: Incorrect because boiling dry destroys the titration setup. C: Incorrect because mass alone does not identify the endpoint. D: Incorrect because a metal strip is not the standard endpoint detector.
CSS - PMS - CCE - PCS - General Science
Acid/Base
When [A⁻] equals [HA] in an acidic buffer, the pH is:
A. Equal to pKa
B. Always 7
C. Equal to 14
D. Equal to zero
Correct Answer: A
A: Correct because the concentration ratio is 1, log 1 is zero, so pH = pKa. B: Incorrect because a buffer is not necessarily neutral. C: Incorrect because 14 is not generally related to pKa equality. D: Incorrect because pH becomes zero only in very acidic conditions, not because the ratio is one.
CSS - PMS - CCE - PCS - General Science
Acid/Base
The Henderson–Hasselbalch equation for an acidic buffer is:
A. pH = pKa + log([A⁻]/[HA])
B. pH = pKa − log([A⁻]/[HA])
C. pH = 14 + pKa
D. pH = [HA] × [A⁻]
Correct Answer: A
A: Correct because the standard buffer relation is pH = pKa + log of conjugate-base concentration divided by weak-acid concentration. B: Incorrect because the logarithmic term has a plus sign in the standard form. C: Incorrect because adding 14 to pKa is not the buffer equation. D: Incorrect because multiplying concentrations does not directly give pH.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Which pair forms a basic buffer?
A. NH₃ and NH₄Cl
B. NaOH and NaCl
C. HCl and KCl
D. H₂SO₄ and Na₂SO₄
Correct Answer: A
A: Correct because NH₃ is a weak base and NH₄Cl supplies its conjugate acid, NH₄⁺. B: Incorrect because NaOH is strong and NaCl is not its conjugate-acid salt. C: Incorrect because HCl and KCl do not form a weak base/conjugate-acid pair. D: Incorrect because H₂SO₄ is a strong acid system, not the standard basic buffer pair.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Which pair forms an acidic buffer?
A. CH₃COOH and CH₃COONa
B. HCl and NaCl
C. NaOH and NaCl
D. HNO₃ and KNO₃
Correct Answer: A
A: Correct because acetic acid is weak and sodium acetate supplies its conjugate base. B: Incorrect because HCl is strong and Cl⁻ is too weak a base for useful buffering. C: Incorrect because NaOH with NaCl is not a weak conjugate pair. D: Incorrect because HNO₃ is strong and nitrate does not make an effective buffer pair.
CSS - PMS - CCE - PCS - General Science
Acid/Base
A basic buffer is commonly made from:
A. A weak base and its conjugate-acid salt
B. A strong acid alone
C. A weak acid alone
D. Sodium chloride and water only
Correct Answer: A
A: Correct because a weak base and a salt containing its conjugate acid form a basic buffer. B: Incorrect because a strong acid alone is not a buffer. C: Incorrect because a weak acid alone lacks enough conjugate base for effective buffering. D: Incorrect because NaCl and water do not form a weak conjugate pair.
CSS - PMS - CCE - PCS - General Science
Acid/Base
An acidic buffer is commonly made from:
A. A weak acid and its conjugate-base salt
B. A strong acid and a strong base in equal amounts only
C. A strong base and its salt
D. Pure water and sugar
Correct Answer: A
A: Correct because a weak acid together with a soluble salt containing its conjugate base forms an acidic buffer. B: Incorrect because complete neutralization of strong acid and strong base usually gives a neutral salt solution, not a buffer. C: Incorrect because a weak base and its conjugate-acid salt form a basic buffer. D: Incorrect because water and sugar do not provide a conjugate acid–base system.
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.