, CHEM 121 | Module 7 | Original Acid-Base Chemistry Practice
CHEM 121 Module Exam 7 Portage General
Chemistry w/Lab 100% Correct
1. A student applies the concept of acidic buffer pair during an acid-base equilibrium or titration
problem.Which interpretation is most appropriate?
A) A weak acid and its conjugate base form an acidic buffer pair.
B) A weak acid alone is always an optimal buffer
C) A strong acid and its neutral salt always form a buffer
D) Two strong bases form an acidic buffer
Correct Answer: A weak acid and its conjugate base form an acidic buffer pair.
Rationale: A weak acid and its conjugate base form an acidic buffer pair. Applying this correctly helps determine
species, equilibrium direction, pH, buffer behavior, or titration stoichiometry.
2. Which statement best describes strong acid-strong base equivalence in CHEM 121 Module 7?
A) Its equivalence pH is always above 12
B) Its equivalence pH is always below 2
C) Its equivalence pH equals pKa
D) A strong acid-strong base titration has an equivalence pH near 7 at 25 C.
Correct Answer: A strong acid-strong base titration has an equivalence pH near 7 at 25 C.
Rationale: A strong acid-strong base titration has an equivalence pH near 7 at 25 C. This is a core acid-base
equilibrium principle in the official Module 7 scope.
3. Which statement best describes dilution of weak acid in CHEM 121 Module 7?
A) Dilution changes Ka
B) Dilution generally increases percent ionization of a weak acid.
C) Dilution converts weak acid to strong acid
D) Dilution decreases percent ionization to zero
Correct Answer: Dilution generally increases percent ionization of a weak acid.
Rationale: Dilution generally increases percent ionization of a weak acid. This is a core acid-base equilibrium
principle in the official Module 7 scope.
4. A student applies the concept of Arrhenius acid during an acid-base equilibrium or titration
problem.Which interpretation is most appropriate?
A) It must accept an electron pair
B) It cannot ionize in water
C) An Arrhenius acid increases H3O+ concentration in water.
D) It increases OH- concentration in water
Correct Answer: An Arrhenius acid increases H3O+ concentration in water.
Rationale: An Arrhenius acid increases H3O+ concentration in water. Applying this correctly helps determine
species, equilibrium direction, pH, buffer behavior, or titration stoichiometry.
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, CHEM 121 | Module 7 | Original Acid-Base Chemistry Practice
5. What is the approximate pH of 0.0010 M NaOH at 25 C?
A) 13.00
B) 3.00
C) 11.00
D) 0.0010
Correct Answer: 11.00
Rationale: pOH = 3.00, so pH = 14.00 - 3.00 = 11.00.
6. Which statement best describes 5 percent rule in CHEM 121 Module 7?
A) The cutoff is always 50%
B) The small-x approximation is commonly considered reasonable when x is less than about 5% of the
initialconcentration.
C) The approximation is always valid
D) The rule applies only to strong acids
Correct Answer: The small-x approximation is commonly considered reasonable when x is less than about 5%
of the initial concentration.
Rationale: The small-x approximation is commonly considered reasonable when x is less than about 5% of the initial
concentration. This is a core acid-base equilibrium principle in the official Module 7 scope.
7. Which statement best describes buret technique in CHEM 121 Module 7?
A) Burets should be read to whole milliliters only
B) Only the final reading matters
C) Read from above to prevent parallax
D) A buret should be read at eye level and initial and final readings should both be recorded.
Correct Answer: A buret should be read at eye level and initial and final readings should both be recorded.
Rationale: A buret should be read at eye level and initial and final readings should both be recorded. This is a core
acid-base equilibrium principle in the official Module 7 scope.
8. 25.0 mL of a monoprotic acid requires 30.0 mL of 0.200 M NaOH at equivalence. What is the
acidmolarity?
A) 0.167 M
B) 0.200 M
C) 0.300 M
D) 0.240 M
Correct Answer: 0.240 M
Rationale: Moles NaOH = 0.0300 L x 0.200 M = 0.00600 mol. For 1:1 stoichiometry, acid molarity = 0.00600/0.0250 =
0.240 M.
9. Which statement best describes pH-pOH relation in CHEM 121 Module 7?
A) At 25 C, pH + pOH = 14.00.
B) pH x pOH = 14
C) pH - pOH = 14
D) pH + pOH = 7
Page 3
CHEM 121 Module Exam 7 Portage General
Chemistry w/Lab 100% Correct
1. A student applies the concept of acidic buffer pair during an acid-base equilibrium or titration
problem.Which interpretation is most appropriate?
A) A weak acid and its conjugate base form an acidic buffer pair.
B) A weak acid alone is always an optimal buffer
C) A strong acid and its neutral salt always form a buffer
D) Two strong bases form an acidic buffer
Correct Answer: A weak acid and its conjugate base form an acidic buffer pair.
Rationale: A weak acid and its conjugate base form an acidic buffer pair. Applying this correctly helps determine
species, equilibrium direction, pH, buffer behavior, or titration stoichiometry.
2. Which statement best describes strong acid-strong base equivalence in CHEM 121 Module 7?
A) Its equivalence pH is always above 12
B) Its equivalence pH is always below 2
C) Its equivalence pH equals pKa
D) A strong acid-strong base titration has an equivalence pH near 7 at 25 C.
Correct Answer: A strong acid-strong base titration has an equivalence pH near 7 at 25 C.
Rationale: A strong acid-strong base titration has an equivalence pH near 7 at 25 C. This is a core acid-base
equilibrium principle in the official Module 7 scope.
3. Which statement best describes dilution of weak acid in CHEM 121 Module 7?
A) Dilution changes Ka
B) Dilution generally increases percent ionization of a weak acid.
C) Dilution converts weak acid to strong acid
D) Dilution decreases percent ionization to zero
Correct Answer: Dilution generally increases percent ionization of a weak acid.
Rationale: Dilution generally increases percent ionization of a weak acid. This is a core acid-base equilibrium
principle in the official Module 7 scope.
4. A student applies the concept of Arrhenius acid during an acid-base equilibrium or titration
problem.Which interpretation is most appropriate?
A) It must accept an electron pair
B) It cannot ionize in water
C) An Arrhenius acid increases H3O+ concentration in water.
D) It increases OH- concentration in water
Correct Answer: An Arrhenius acid increases H3O+ concentration in water.
Rationale: An Arrhenius acid increases H3O+ concentration in water. Applying this correctly helps determine
species, equilibrium direction, pH, buffer behavior, or titration stoichiometry.
Page 2
, CHEM 121 | Module 7 | Original Acid-Base Chemistry Practice
5. What is the approximate pH of 0.0010 M NaOH at 25 C?
A) 13.00
B) 3.00
C) 11.00
D) 0.0010
Correct Answer: 11.00
Rationale: pOH = 3.00, so pH = 14.00 - 3.00 = 11.00.
6. Which statement best describes 5 percent rule in CHEM 121 Module 7?
A) The cutoff is always 50%
B) The small-x approximation is commonly considered reasonable when x is less than about 5% of the
initialconcentration.
C) The approximation is always valid
D) The rule applies only to strong acids
Correct Answer: The small-x approximation is commonly considered reasonable when x is less than about 5%
of the initial concentration.
Rationale: The small-x approximation is commonly considered reasonable when x is less than about 5% of the initial
concentration. This is a core acid-base equilibrium principle in the official Module 7 scope.
7. Which statement best describes buret technique in CHEM 121 Module 7?
A) Burets should be read to whole milliliters only
B) Only the final reading matters
C) Read from above to prevent parallax
D) A buret should be read at eye level and initial and final readings should both be recorded.
Correct Answer: A buret should be read at eye level and initial and final readings should both be recorded.
Rationale: A buret should be read at eye level and initial and final readings should both be recorded. This is a core
acid-base equilibrium principle in the official Module 7 scope.
8. 25.0 mL of a monoprotic acid requires 30.0 mL of 0.200 M NaOH at equivalence. What is the
acidmolarity?
A) 0.167 M
B) 0.200 M
C) 0.300 M
D) 0.240 M
Correct Answer: 0.240 M
Rationale: Moles NaOH = 0.0300 L x 0.200 M = 0.00600 mol. For 1:1 stoichiometry, acid molarity = 0.00600/0.0250 =
0.240 M.
9. Which statement best describes pH-pOH relation in CHEM 121 Module 7?
A) At 25 C, pH + pOH = 14.00.
B) pH x pOH = 14
C) pH - pOH = 14
D) pH + pOH = 7
Page 3
