Portage Learning CHEM 210 Biochemistry
Module 1 Exam | Actual Water pH Buffers
and Thermodynamics Assessment with
Answers
DOMAIN: WATER & HYDROGEN BONDING (20%)
Q1. Which of the following correctly describes hydrogen bonding in water?
A. A covalent bond between a hydrogen atom of one water molecule and the oxygen
atom of another
B. A weak electrostatic attraction between the partially positive hydrogen of one water
molecule and the partially negative oxygen of another
C. An ionic bond formed between water molecules
D. A van der Waals interaction between adjacent water molecules
Correct Answer: B
Rationale: B. [CORRECT] Hydrogen bonding is a weak electrostatic attraction (not a
covalent bond) between a hydrogen atom covalently bonded to an electronegative atom
(oxygen in water) and a lone pair on an adjacent electronegative atom. Each water
molecule can form up to four hydrogen bonds (two as donor via H atoms, two as
acceptor via lone pairs on oxygen). This network gives water its unique properties. A is
,incorrect; this describes a covalent O-H bond within a single water molecule, not
between molecules. C is incorrect; hydrogen bonds are not ionic bonds; ionic bonds
involve complete electron transfer and electrostatic attraction between ions. D is
incorrect; while van der Waals forces exist between all molecules, hydrogen bonds are
specific, stronger interactions (10-40 kJ/mol vs. ~1 kJ/mol for van der Waals).
Q2. The hydrophobic effect refers to:
A. The strong attraction between water molecules
B. The tendency of nonpolar molecules to aggregate in aqueous solution to minimize
contact with water
C. The ability of water to dissolve ionic compounds
D. The formation of hydrogen bonds between water and nonpolar molecules
Correct Answer: B
Rationale: B. [CORRECT] The hydrophobic effect is the tendency of nonpolar molecules
to associate with each other in aqueous solution, driven by the increase in entropy of
water molecules as they are released from ordered hydration shells ("cages") around
nonpolar solutes. This is primarily an entropic phenomenon, not an attractive force
between nonpolar molecules. A is incorrect; this describes water cohesion or hydrogen
bonding between water molecules. C is incorrect; this describes water's solvent
properties for ionic compounds due to its high dielectric constant. D is incorrect; water
cannot form favorable hydrogen bonds with nonpolar molecules; this is precisely why
nonpolar substances are excluded.
,Q3. Which of the following properties of water is most responsible for its high specific
heat capacity?
A. Its small molecular size
B. The extensive hydrogen bonding network that requires significant energy to disrupt
C. Its ability to form ionic bonds
D. Its low molecular weight
Correct Answer: B
Rationale: B. [CORRECT] Water's high specific heat capacity (4.186 J/g·°C) results from
the extensive hydrogen bonding network. Breaking these intermolecular hydrogen
bonds requires substantial energy input, allowing water to absorb large amounts of heat
with minimal temperature change. This property is crucial for temperature regulation in
biological systems. A is incorrect; small molecular size would actually correlate with
lower heat capacity. C is incorrect; water does not form ionic bonds; it forms hydrogen
bonds and can solvate ions. D is incorrect; low molecular weight does not determine
heat capacity; hydrogen bonding is the key factor.
Q4. [HYDROPHOBIC EFFECT] The hydrophobic effect is primarily driven by:
A. Enthalpic stabilization from favorable interactions between nonpolar molecules
B. Entropic increase as water molecules are released from ordered hydration shells
C. Covalent bond formation between nonpolar side chains
D. Electrostatic attraction between nonpolar molecules
Correct Answer: B
, Rationale: B. [CORRECT] The hydrophobic effect is entropically driven (ΔS>0 ). Water
molecules form ordered, low-entropy "cages" (clathrate structures) around nonpolar
solutes. When nonpolar molecules aggregate, these ordered water molecules are
released into bulk water with higher entropy. The positive entropy change drives the
process, despite the enthalpy change being small or slightly unfavorable. A is incorrect;
enthalpy changes (ΔH ) in hydrophobic interactions are typically small or slightly
positive; the driving force is entropy, not enthalpy. C is incorrect; hydrophobic
interactions are non-covalent; no covalent bonds form between nonpolar molecules. D
is incorrect; nonpolar molecules lack significant partial charges for electrostatic
attraction.
Q5. Which of the following best explains why ice is less dense than liquid water?
A. Ice has fewer hydrogen bonds than liquid water
B. Ice forms a crystalline lattice with hydrogen bonds holding molecules in fixed
positions, creating more space between molecules
C. Ice has a higher kinetic energy than liquid water
D. Ice molecules are smaller than liquid water molecules
Correct Answer: B
Rationale: B. [CORRECT] In ice, each water molecule forms four hydrogen bonds in a
tetrahedral arrangement, creating an open hexagonal crystalline lattice with empty
spaces. This structure is less dense than liquid water, where molecules are closer
together and hydrogen bonds constantly break and reform. This explains why ice floats.
A is incorrect; ice has more stable hydrogen bonds, not fewer. C is incorrect; ice has
Module 1 Exam | Actual Water pH Buffers
and Thermodynamics Assessment with
Answers
DOMAIN: WATER & HYDROGEN BONDING (20%)
Q1. Which of the following correctly describes hydrogen bonding in water?
A. A covalent bond between a hydrogen atom of one water molecule and the oxygen
atom of another
B. A weak electrostatic attraction between the partially positive hydrogen of one water
molecule and the partially negative oxygen of another
C. An ionic bond formed between water molecules
D. A van der Waals interaction between adjacent water molecules
Correct Answer: B
Rationale: B. [CORRECT] Hydrogen bonding is a weak electrostatic attraction (not a
covalent bond) between a hydrogen atom covalently bonded to an electronegative atom
(oxygen in water) and a lone pair on an adjacent electronegative atom. Each water
molecule can form up to four hydrogen bonds (two as donor via H atoms, two as
acceptor via lone pairs on oxygen). This network gives water its unique properties. A is
,incorrect; this describes a covalent O-H bond within a single water molecule, not
between molecules. C is incorrect; hydrogen bonds are not ionic bonds; ionic bonds
involve complete electron transfer and electrostatic attraction between ions. D is
incorrect; while van der Waals forces exist between all molecules, hydrogen bonds are
specific, stronger interactions (10-40 kJ/mol vs. ~1 kJ/mol for van der Waals).
Q2. The hydrophobic effect refers to:
A. The strong attraction between water molecules
B. The tendency of nonpolar molecules to aggregate in aqueous solution to minimize
contact with water
C. The ability of water to dissolve ionic compounds
D. The formation of hydrogen bonds between water and nonpolar molecules
Correct Answer: B
Rationale: B. [CORRECT] The hydrophobic effect is the tendency of nonpolar molecules
to associate with each other in aqueous solution, driven by the increase in entropy of
water molecules as they are released from ordered hydration shells ("cages") around
nonpolar solutes. This is primarily an entropic phenomenon, not an attractive force
between nonpolar molecules. A is incorrect; this describes water cohesion or hydrogen
bonding between water molecules. C is incorrect; this describes water's solvent
properties for ionic compounds due to its high dielectric constant. D is incorrect; water
cannot form favorable hydrogen bonds with nonpolar molecules; this is precisely why
nonpolar substances are excluded.
,Q3. Which of the following properties of water is most responsible for its high specific
heat capacity?
A. Its small molecular size
B. The extensive hydrogen bonding network that requires significant energy to disrupt
C. Its ability to form ionic bonds
D. Its low molecular weight
Correct Answer: B
Rationale: B. [CORRECT] Water's high specific heat capacity (4.186 J/g·°C) results from
the extensive hydrogen bonding network. Breaking these intermolecular hydrogen
bonds requires substantial energy input, allowing water to absorb large amounts of heat
with minimal temperature change. This property is crucial for temperature regulation in
biological systems. A is incorrect; small molecular size would actually correlate with
lower heat capacity. C is incorrect; water does not form ionic bonds; it forms hydrogen
bonds and can solvate ions. D is incorrect; low molecular weight does not determine
heat capacity; hydrogen bonding is the key factor.
Q4. [HYDROPHOBIC EFFECT] The hydrophobic effect is primarily driven by:
A. Enthalpic stabilization from favorable interactions between nonpolar molecules
B. Entropic increase as water molecules are released from ordered hydration shells
C. Covalent bond formation between nonpolar side chains
D. Electrostatic attraction between nonpolar molecules
Correct Answer: B
, Rationale: B. [CORRECT] The hydrophobic effect is entropically driven (ΔS>0 ). Water
molecules form ordered, low-entropy "cages" (clathrate structures) around nonpolar
solutes. When nonpolar molecules aggregate, these ordered water molecules are
released into bulk water with higher entropy. The positive entropy change drives the
process, despite the enthalpy change being small or slightly unfavorable. A is incorrect;
enthalpy changes (ΔH ) in hydrophobic interactions are typically small or slightly
positive; the driving force is entropy, not enthalpy. C is incorrect; hydrophobic
interactions are non-covalent; no covalent bonds form between nonpolar molecules. D
is incorrect; nonpolar molecules lack significant partial charges for electrostatic
attraction.
Q5. Which of the following best explains why ice is less dense than liquid water?
A. Ice has fewer hydrogen bonds than liquid water
B. Ice forms a crystalline lattice with hydrogen bonds holding molecules in fixed
positions, creating more space between molecules
C. Ice has a higher kinetic energy than liquid water
D. Ice molecules are smaller than liquid water molecules
Correct Answer: B
Rationale: B. [CORRECT] In ice, each water molecule forms four hydrogen bonds in a
tetrahedral arrangement, creating an open hexagonal crystalline lattice with empty
spaces. This structure is less dense than liquid water, where molecules are closer
together and hydrogen bonds constantly break and reform. This explains why ice floats.
A is incorrect; ice has more stable hydrogen bonds, not fewer. C is incorrect; ice has
