PORTAGE LEARNING CHEM 210 MODULE 2 PROBLEM
SET QUESTIONS WITH ANSWERS AND EXPLANATIONS
Question 1.
A buffer has pKa = 7.2, [A-] = 1.0 mM, and [HA] = 4.0 mM. What pH is predicted by
Henderson-Hasselbalch?
A. 7.40
B. 6.60
C. 7.20
D. 7.80
Correct Answer: B. 6.60
Explanation: Use pH = pKa + log([A-]/[HA]). The ratio is 0.25, giving pH = 6.60. When
base exceeds acid, pH lies above pKa; when acid exceeds base, it lies below pKa.
Question 2.
A laboratory observation shows that after donation, the acid becomes its conjugate base.
Which concept best explains this finding?
A. Carbonic anhydrase
B. Ice less dense than liquid water
C. Bronsted-Lowry acid
D. Autoionization of water
Correct Answer: C. Bronsted-Lowry acid
Explanation: Bronsted-Lowry acid best explains the observation because a
Bronsted-Lowry acid donates a proton to another species. The clue in the stem points
directly to this mechanism or structural feature. The other options involve different
biochemical properties and therefore do not account for the observation as well.
Question 3.
Which statement about Gibbs free energy, Delta G is most accurate?
A. Cohesion is attraction between molecules of the same substance, as in water-water
attraction.
B. A Bronsted-Lowry acid donates a proton to another species.
C. Ion-dipole attractions occur between a charged ion and the partial charges of a polar
molecule.
D. Delta G predicts whether a process is thermodynamically favorable under specified
conditions.
Correct Answer: D. Delta G predicts whether a process is thermodynamically
favorable under specified conditions.
Explanation: Delta G predicts whether a process is thermodynamically favorable under
specified conditions. This is the defining chemistry of Gibbs free energy, Delta G. The
alternative statements describe other concepts and would misclassify the structure, force,
,or process under discussion.
Question 4.
A laboratory observation shows that hydrocarbon groups tend to aggregate away from
water. Which concept best explains this finding?
A. Hydrophobic effect
B. Buffer
C. Henderson-Hasselbalch equation
D. Hydrogen bond acceptor
Correct Answer: A. Hydrophobic effect
Explanation: Hydrophobic effect best explains the observation because nonpolar groups
cluster in water because doing so reduces ordered water cages and increases overall
solvent entropy. The clue in the stem points directly to this mechanism or structural
feature. The other options involve different biochemical properties and therefore do not
account for the observation as well.
Question 5.
Which statement about Autoionization of water is most accurate?
A. A molecule donates a hydrogen bond when an electronegative atom bearing H provides
that hydrogen to an acceptor.
B. Cohesion is attraction between molecules of the same substance, as in water-water
attraction.
C. Water can reversibly transfer a proton between molecules to form H3O+ and OH-.
D. Water requires substantial energy to move from liquid to gas because many
intermolecular hydrogen bonds must be disrupted.
Correct Answer: C. Water can reversibly transfer a proton between molecules to
form H3O+ and OH-.
Explanation: Water can reversibly transfer a proton between molecules to form H3O+
and OH-. This is the defining chemistry of Autoionization of water. The alternative
statements describe other concepts and would misclassify the structure, force, or process
under discussion.
Question 6.
A laboratory observation shows that nonpolar molecules can still attract weakly at close
range. Which concept best explains this finding?
A. Surface tension
B. Bicarbonate buffer system
C. Acid dissociation constant, Ka
D. London dispersion force
Correct Answer: D. London dispersion force
,Explanation: London dispersion force best explains the observation because london
dispersion forces arise from temporary fluctuations in electron distribution and occur in all
atoms and molecules. The clue in the stem points directly to this mechanism or structural
feature. The other options involve different biochemical properties and therefore do not
account for the observation as well.
Question 7.
Which statement about Ion product of water, Kw is most accurate?
A. At 25 C, Kw equals [H+][OH-] and is approximately 1.0 x 10^-14.
B. A buffer is most effective when pH is within roughly one pH unit of the buffer pKa.
C. Delta H describes the heat-content change of a process at constant pressure.
D. pH is the negative base-10 logarithm of the hydrogen ion concentration.
Correct Answer: A. At 25 C, Kw equals [H+][OH-] and is approximately 1.0 x
10^-14.
Explanation: At 25 C, Kw equals [H+][OH-] and is approximately 1.0 x 10^-14. This is the
defining chemistry of Ion product of water, Kw. The alternative statements describe other
concepts and would misclassify the structure, force, or process under discussion.
Question 8.
A laboratory observation shows that after proton acceptance, the base becomes its
conjugate acid. Which concept best explains this finding?
A. Optimal buffer range
B. Bronsted-Lowry base
C. Dipole-dipole interaction
D. Phosphate buffer system
Correct Answer: B. Bronsted-Lowry base
Explanation: Bronsted-Lowry base best explains the observation because a
Bronsted-Lowry base accepts a proton from another species. The clue in the stem points
directly to this mechanism or structural feature. The other options involve different
biochemical properties and therefore do not account for the observation as well.
Question 9.
A buffer has pKa = 9.2, [A-] = 3.0 mM, and [HA] = 1.0 mM. What pH is predicted by
Henderson-Hasselbalch?
A. 4.32
B. 9.20
C. 9.68
D. 8.72
Correct Answer: C. 9.68
Explanation: Use pH = pKa + log([A-]/[HA]). The ratio is 3.00, giving pH = 9.68. When
base exceeds acid, pH lies above pKa; when acid exceeds base, it lies below pKa.
, Question 10.
A laboratory observation shows that phosphate can accept or donate protons near
physiologic conditions. Which concept best explains this finding?
A. Phosphate buffer system
B. Acid dissociation constant, Ka
C. pOH
D. Weak acid
Correct Answer: A. Phosphate buffer system
Explanation: Phosphate buffer system best explains the observation because the
H2PO4-/HPO4^2- pair is an important intracellular and renal buffer system. The clue in the
stem points directly to this mechanism or structural feature. The other options involve
different biochemical properties and therefore do not account for the observation as well.
Question 11.
Which statement about Water polarity is most accurate?
A. A molecule donates a hydrogen bond when an electronegative atom bearing H provides
that hydrogen to an acceptor.
B. Unequal sharing of electrons in O-H bonds makes oxygen partially negative and
hydrogen partially positive.
C. Ka quantifies the extent to which an acid dissociates in water; larger Ka values indicate
stronger acids.
D. An exergonic process has negative Delta G and can proceed spontaneously in the
thermodynamic sense.
Correct Answer: B. Unequal sharing of electrons in O-H bonds makes oxygen
partially negative and hydrogen partially positive.
Explanation: Unequal sharing of electrons in O-H bonds makes oxygen partially negative
and hydrogen partially positive. This is the defining chemistry of Water polarity. The
alternative statements describe other concepts and would misclassify the structure, force,
or process under discussion.
Question 12.
A laboratory observation shows that ionic and polar solutes interact strongly with water.
Which concept best explains this finding?
A. Hydrogen bond donor
B. Acid dissociation constant, Ka
C. Exergonic process
D. Water polarity
Correct Answer: D. Water polarity
Explanation: Water polarity best explains the observation because unequal sharing of
electrons in O-H bonds makes oxygen partially negative and hydrogen partially positive.
SET QUESTIONS WITH ANSWERS AND EXPLANATIONS
Question 1.
A buffer has pKa = 7.2, [A-] = 1.0 mM, and [HA] = 4.0 mM. What pH is predicted by
Henderson-Hasselbalch?
A. 7.40
B. 6.60
C. 7.20
D. 7.80
Correct Answer: B. 6.60
Explanation: Use pH = pKa + log([A-]/[HA]). The ratio is 0.25, giving pH = 6.60. When
base exceeds acid, pH lies above pKa; when acid exceeds base, it lies below pKa.
Question 2.
A laboratory observation shows that after donation, the acid becomes its conjugate base.
Which concept best explains this finding?
A. Carbonic anhydrase
B. Ice less dense than liquid water
C. Bronsted-Lowry acid
D. Autoionization of water
Correct Answer: C. Bronsted-Lowry acid
Explanation: Bronsted-Lowry acid best explains the observation because a
Bronsted-Lowry acid donates a proton to another species. The clue in the stem points
directly to this mechanism or structural feature. The other options involve different
biochemical properties and therefore do not account for the observation as well.
Question 3.
Which statement about Gibbs free energy, Delta G is most accurate?
A. Cohesion is attraction between molecules of the same substance, as in water-water
attraction.
B. A Bronsted-Lowry acid donates a proton to another species.
C. Ion-dipole attractions occur between a charged ion and the partial charges of a polar
molecule.
D. Delta G predicts whether a process is thermodynamically favorable under specified
conditions.
Correct Answer: D. Delta G predicts whether a process is thermodynamically
favorable under specified conditions.
Explanation: Delta G predicts whether a process is thermodynamically favorable under
specified conditions. This is the defining chemistry of Gibbs free energy, Delta G. The
alternative statements describe other concepts and would misclassify the structure, force,
,or process under discussion.
Question 4.
A laboratory observation shows that hydrocarbon groups tend to aggregate away from
water. Which concept best explains this finding?
A. Hydrophobic effect
B. Buffer
C. Henderson-Hasselbalch equation
D. Hydrogen bond acceptor
Correct Answer: A. Hydrophobic effect
Explanation: Hydrophobic effect best explains the observation because nonpolar groups
cluster in water because doing so reduces ordered water cages and increases overall
solvent entropy. The clue in the stem points directly to this mechanism or structural
feature. The other options involve different biochemical properties and therefore do not
account for the observation as well.
Question 5.
Which statement about Autoionization of water is most accurate?
A. A molecule donates a hydrogen bond when an electronegative atom bearing H provides
that hydrogen to an acceptor.
B. Cohesion is attraction between molecules of the same substance, as in water-water
attraction.
C. Water can reversibly transfer a proton between molecules to form H3O+ and OH-.
D. Water requires substantial energy to move from liquid to gas because many
intermolecular hydrogen bonds must be disrupted.
Correct Answer: C. Water can reversibly transfer a proton between molecules to
form H3O+ and OH-.
Explanation: Water can reversibly transfer a proton between molecules to form H3O+
and OH-. This is the defining chemistry of Autoionization of water. The alternative
statements describe other concepts and would misclassify the structure, force, or process
under discussion.
Question 6.
A laboratory observation shows that nonpolar molecules can still attract weakly at close
range. Which concept best explains this finding?
A. Surface tension
B. Bicarbonate buffer system
C. Acid dissociation constant, Ka
D. London dispersion force
Correct Answer: D. London dispersion force
,Explanation: London dispersion force best explains the observation because london
dispersion forces arise from temporary fluctuations in electron distribution and occur in all
atoms and molecules. The clue in the stem points directly to this mechanism or structural
feature. The other options involve different biochemical properties and therefore do not
account for the observation as well.
Question 7.
Which statement about Ion product of water, Kw is most accurate?
A. At 25 C, Kw equals [H+][OH-] and is approximately 1.0 x 10^-14.
B. A buffer is most effective when pH is within roughly one pH unit of the buffer pKa.
C. Delta H describes the heat-content change of a process at constant pressure.
D. pH is the negative base-10 logarithm of the hydrogen ion concentration.
Correct Answer: A. At 25 C, Kw equals [H+][OH-] and is approximately 1.0 x
10^-14.
Explanation: At 25 C, Kw equals [H+][OH-] and is approximately 1.0 x 10^-14. This is the
defining chemistry of Ion product of water, Kw. The alternative statements describe other
concepts and would misclassify the structure, force, or process under discussion.
Question 8.
A laboratory observation shows that after proton acceptance, the base becomes its
conjugate acid. Which concept best explains this finding?
A. Optimal buffer range
B. Bronsted-Lowry base
C. Dipole-dipole interaction
D. Phosphate buffer system
Correct Answer: B. Bronsted-Lowry base
Explanation: Bronsted-Lowry base best explains the observation because a
Bronsted-Lowry base accepts a proton from another species. The clue in the stem points
directly to this mechanism or structural feature. The other options involve different
biochemical properties and therefore do not account for the observation as well.
Question 9.
A buffer has pKa = 9.2, [A-] = 3.0 mM, and [HA] = 1.0 mM. What pH is predicted by
Henderson-Hasselbalch?
A. 4.32
B. 9.20
C. 9.68
D. 8.72
Correct Answer: C. 9.68
Explanation: Use pH = pKa + log([A-]/[HA]). The ratio is 3.00, giving pH = 9.68. When
base exceeds acid, pH lies above pKa; when acid exceeds base, it lies below pKa.
, Question 10.
A laboratory observation shows that phosphate can accept or donate protons near
physiologic conditions. Which concept best explains this finding?
A. Phosphate buffer system
B. Acid dissociation constant, Ka
C. pOH
D. Weak acid
Correct Answer: A. Phosphate buffer system
Explanation: Phosphate buffer system best explains the observation because the
H2PO4-/HPO4^2- pair is an important intracellular and renal buffer system. The clue in the
stem points directly to this mechanism or structural feature. The other options involve
different biochemical properties and therefore do not account for the observation as well.
Question 11.
Which statement about Water polarity is most accurate?
A. A molecule donates a hydrogen bond when an electronegative atom bearing H provides
that hydrogen to an acceptor.
B. Unequal sharing of electrons in O-H bonds makes oxygen partially negative and
hydrogen partially positive.
C. Ka quantifies the extent to which an acid dissociates in water; larger Ka values indicate
stronger acids.
D. An exergonic process has negative Delta G and can proceed spontaneously in the
thermodynamic sense.
Correct Answer: B. Unequal sharing of electrons in O-H bonds makes oxygen
partially negative and hydrogen partially positive.
Explanation: Unequal sharing of electrons in O-H bonds makes oxygen partially negative
and hydrogen partially positive. This is the defining chemistry of Water polarity. The
alternative statements describe other concepts and would misclassify the structure, force,
or process under discussion.
Question 12.
A laboratory observation shows that ionic and polar solutes interact strongly with water.
Which concept best explains this finding?
A. Hydrogen bond donor
B. Acid dissociation constant, Ka
C. Exergonic process
D. Water polarity
Correct Answer: D. Water polarity
Explanation: Water polarity best explains the observation because unequal sharing of
electrons in O-H bonds makes oxygen partially negative and hydrogen partially positive.
