CSS - PMS - CCE - PCS - General Science
Acid/Base
What is the safest general rule when diluting a concentrated acid?
A. Add acid slowly to water
B. Add water rapidly to acid
C. Mix with bare hands
D. Heat the acid first
Correct Answer: A
A: Correct because adding acid slowly to a larger amount of water allows heat to dissipate and reduces dangerous splashing. B: Incorrect because water added to concentrated acid can heat suddenly, boil, and splash. C: Incorrect because direct skin contact is dangerous. D: Incorrect because heating concentrated acid increases the hazard.
CSS - PMS - CCE - PCS - General Science
Acid/Base
Neutralization of a strong acid by a strong base is usually:
A. Exothermic
B. Endothermic in every case
C. A nuclear reaction
D. Without any energy change
Correct Answer: A
A: Correct because formation of water from H⁺ and OH⁻ releases heat, making strong acid–strong base neutralization exothermic. B: Incorrect because the standard reaction releases rather than absorbs heat. C: Incorrect because it involves electrons and ions, not nuclear changes. D: Incorrect because a measurable enthalpy change occurs.
CSS - PMS - CCE - PCS - General Science
Acid/Base
In Brønsted–Lowry terms, an acid–base reaction involves:
A. Transfer of a proton
B. Transfer of a neutron
C. Creation of mass
D. Only transfer of oxygen
Correct Answer: A
A: Correct because Brønsted–Lowry acid–base reactions are proton-transfer reactions. B: Incorrect because neutron transfer is a nuclear process. C: Incorrect because mass is conserved rather than created. D: Incorrect because oxygen transfer defines some redox ideas, not all acid–base reactions.
CSS - PMS - CCE - PCS - General Science
Acid/Base
A metal oxide that forms a base with water may be called:
A. Acid anhydride
B. Base anhydride
C. Conjugate acid
D. Buffer salt
Correct Answer: B
A: Incorrect because acid anhydrides form acids. B: Correct because a basic metal oxide can be considered the anhydride of the corresponding hydroxide base. C: Incorrect because a conjugate acid differs from a base by one proton. D: Incorrect because a single metal oxide is not automatically a buffer salt.
CSS - PMS - CCE - PCS - General Science
Acid/Base
A nonmetal oxide that forms an acid with water may be called:
A. Acid anhydride
B. Base anhydride
C. Neutral salt
D. Metal hydride
Correct Answer: A
A: Correct because an acidic nonmetal oxide can be viewed as the anhydride of the corresponding oxyacid. B: Incorrect because a base anhydride forms a base with water. C: Incorrect because an oxide is not a neutral salt. D: Incorrect because a hydride contains hydrogen bonded to another element.
CSS - PMS - CCE - PCS - General Science
Acid/Base
In water, a free H⁺ ion is commonly represented more realistically as:
A. H₃O⁺
B. H₂
C. OH⁻
D. O²⁻
Correct Answer: A
A: Correct because a proton associates strongly with water molecules, commonly represented as hydronium, H₃O⁺. B: Incorrect because H₂ is molecular hydrogen. C: Incorrect because OH⁻ is hydroxide. D: Incorrect because O²⁻ does not exist freely in ordinary water.
CSS - PMS - CCE - PCS - General Science
Acid/Base
At 25°C, an acidic aqueous solution normally has [OH⁻]:
A. Greater than 1 × 10⁻⁷ M
B. Equal to 1 × 10⁻⁷ M
C. Less than 1 × 10⁻⁷ M
D. Always zero
Correct Answer: C
A: Incorrect because values above 10⁻⁷ M indicate basicity. B: Incorrect because equality occurs in neutral water. C: Correct because in an acidic solution [H⁺] exceeds 10⁻⁷ M, so [OH⁻] is below 10⁻⁷ M while their product remains Kw. D: Incorrect because OH⁻ is not exactly zero because water equilibrium persists.
CSS - PMS - CCE - PCS - General Science
Acid/Base
For a weak base, the base-dissociation constant is represented by:
A. Ka
B. Kb
C. Kw
D. Kc only
Correct Answer: B
A: Incorrect because Ka is used for acids. B: Correct because Kb quantifies the equilibrium ionization or proton-accepting behavior of a weak base in water. C: Incorrect because Kw refers to water autoionization. D: Incorrect because Kc is a general equilibrium constant, but Kb is the specific base constant.
CSS - PMS - CCE - PCS - General Science
Acid/Base
A lower pKa value generally indicates:
A. A stronger acid
B. A weaker acid
C. A stronger conjugate base
D. No relationship to acid strength
Correct Answer: A
A: Correct because pKa = −log Ka, so a lower pKa corresponds to a larger Ka and stronger acid. B: Incorrect because weaker acids have higher pKa values. C: Incorrect because the conjugate base of a stronger acid is generally weaker. D: Incorrect because pKa is directly related to acid strength.
CSS - PMS - CCE - PCS - General Science
Acid/Base
A larger Ka value generally indicates:
A. A stronger acid
B. A weaker acid
C. A stronger base only
D. A neutral salt only
Correct Answer: A
A: Correct because a larger Ka means the acid equilibrium lies further toward ionized products. B: Incorrect because a weaker acid has a smaller Ka. C: Incorrect because Ka describes acid strength, not base strength alone. D: Incorrect because neutral salts are not classified by acid Ka in this way.
CSS - PMS - CCE - PCS - General Science
Acid/Base
For a weak acid, the acid-dissociation constant is represented by:
A. Ka
B. Kb
C. Kw
D. Ksp
Correct Answer: A
A: Correct because Ka quantifies the ionization equilibrium of an acid. B: Incorrect because Kb is the base-dissociation constant. C: Incorrect because Kw is the ionic product of water. D: Incorrect because Ksp is the solubility-product constant.
CSS - PMS - CCE - PCS - General Science
Acid/Base
The common-ion effect generally causes the ionization of a weak electrolyte to:
A. Increase greatly
B. Decrease
C. Remain exactly unchanged
D. Become nuclear
Correct Answer: B
A: Incorrect because Le Châtelier's principle predicts suppression, not a large increase. B: Correct because adding an ion already present shifts the equilibrium toward the unionized weak electrolyte. C: Incorrect because equilibrium composition changes. D: Incorrect because nuclear change is unrelated.
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.