CSS - PMS - CCE - PCS - General Science
Acid/Base
An aqueous solution of Na₂CO₃ is generally:
A. Acidic
B. Basic
C. Neutral
D. Always pH 1
Correct Answer: B
A: Incorrect because carbonate does not make the solution acidic. B: Correct because CO₃²⁻ is the conjugate base of a weak acid and hydrolyzes water to produce OH⁻. C: Incorrect because hydrolysis prevents exact neutrality. D: Incorrect because pH 1 is strongly acidic and impossible for ordinary sodium carbonate solution.
CSS - PMS - CCE - PCS - General Science
Acid/Base
An aqueous solution of NH₄Cl is generally:
A. Acidic
B. Basic
C. Neutral in all conditions
D. Non-aqueous only
Correct Answer: A
A: Correct because NH₄⁺ is the conjugate acid of the weak base NH₃ and donates protons to water. B: Incorrect because NH₄⁺ hydrolysis does not make the solution basic. C: Incorrect because the solution is not neutral because NH₄⁺ is acidic. D: Incorrect because NH₄Cl readily forms aqueous solutions.
CSS - PMS - CCE - PCS - General Science
Acid/Base
An aqueous solution of NaCl is approximately neutral because NaCl is formed from:
A. A strong acid and a strong base
B. A weak acid and a weak base only
C. A strong acid and a weak base
D. A weak acid and a strong base
Correct Answer: A
A: Correct because NaCl comes from HCl and NaOH; Na⁺ and Cl⁻ undergo negligible hydrolysis. B: Incorrect because weak acid–weak base salts have pH depending on Ka and Kb. C: Incorrect because a strong acid–weak base salt is usually acidic. D: Incorrect because a weak acid–strong base salt is usually basic.
CSS - PMS - CCE - PCS - General Science
Acid/Base
At equivalence, a strong acid titrated with a weak base generally has pH:
A. Less than 7
B. Exactly 7
C. Greater than 7
D. Exactly 14
Correct Answer: A
A: Correct because the conjugate acid of the weak base hydrolyzes water and makes the solution acidic. B: Incorrect because neutral pH is typical of strong acid–strong base equivalence. C: Incorrect because pH above 7 would indicate a basic equivalence solution. D: Incorrect because pH 14 is strongly basic and inappropriate here.
CSS - PMS - CCE - PCS - General Science
Acid/Base
At equivalence, a weak acid titrated with a strong base generally has pH:
A. Less than 7
B. Exactly 7 in every case
C. Greater than 7
D. Exactly 0
Correct Answer: C
A: Incorrect because pH below 7 is typical of strong acid–weak base equivalence. B: Incorrect because the equivalence solution is not neutral because the salt hydrolyzes. C: Correct because the conjugate base of the weak acid hydrolyzes water and makes the solution basic. D: Incorrect because pH zero is far too acidic.
CSS - PMS - CCE - PCS - General Science
Acid/Base
At 25°C, the equivalence-point pH for a strong acid–strong base titration is approximately:
A. 3
B. 5
C. 7
D. 11
Correct Answer: C
A: Incorrect because 3 is acidic. B: Incorrect because 5 is acidic. C: Correct because the resulting salt of a strong acid and strong base is essentially neutral in water, giving pH near 7 at 25°C. D: Incorrect because 11 is basic.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Most acid–base indicators are:
A. Weak organic acids or bases
B. Strong mineral acids only
C. Pure metals
D. Noble gases
Correct Answer: A
A: Correct because indicators are usually weak organic acids or bases whose protonated and deprotonated forms have different colors. B: Incorrect because strong mineral acids do not normally serve as color indicators. C: Incorrect because metals are not ordinary acid–base indicators. D: Incorrect because noble gases are chemically inert and colorless in solution.
CSS - PMS - CCE - PCS - General Science
Acid/Base
A good primary standard should be:
A. Pure, stable, and of known composition
B. Highly volatile and impure
C. Always a gas
D. Rapidly decomposing
Correct Answer: A
A: Correct because high purity, stability, and definite composition allow accurate preparation by direct weighing. B: Incorrect because volatility and impurity cause mass and composition errors. C: Incorrect because primary standards are commonly stable solids, not necessarily gases. D: Incorrect because rapid decomposition prevents accurate use.
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.