CHEM210 Biochemistry
Final Assessment Review
Module 2 (Questions & Solutions)
2025
©2025
, 1. Case Study – Molecular Geometry of Water
An X‑ray diffraction study in a research lab measures the bond angle
between the hydrogen atoms in a water molecule. The measured angle is
found to be approximately 104.5°.
Question: Which of the following best explains this bond angle?
A. The linear arrangement of oxygen and hydrogen atoms
B. Sp³ hybridization of oxygen with two lone pairs causing repulsion
C. Planar trigonal geometry of the water molecule
D. Ionic bonding between hydrogen and oxygen
ANS: B. Sp³ hybridization of oxygen with two lone pairs causing
repulsion
Rationale: Oxygen in H₂O is sp³ hybridized; the two lone pairs occupy
more space than bonding pairs, forcing the H–O–H angle to decrease
from the ideal tetrahedral angle (109.5°) to about 104.5°.
---
2. Case Study – Boiling Point and Hydrogen Bonding
A researcher compares boiling points of H₂O and H₂S. Despite similar
molecular weights, water boils much higher than hydrogen sulfide.
Question: What is the primary reason for water’s high boiling point?
A. Strong ionic bonds in water
B. Extensive hydrogen bonding between water molecules
C. Greater van der Waals forces in water
D. Covalent cross-linking between water molecules
ANS: B. Extensive hydrogen bonding between water molecules
Rationale: Water molecules engage in strong hydrogen bonding, which
requires significantly more energy to break than the weaker van der
Waals interactions present in H₂S.
©2025
,---
3. Case Study – Specific Heat Capacity
In a calorimetry experiment, a student heats a sample of water and
observes that it requires a large amount of energy to raise its
temperature by 1°C.
Question: What property of water does this observation demonstrate?
A. Low heat capacity
B. High specific heat capacity
C. High thermal conductivity
D. Low thermal inertia
ANS: B. High specific heat capacity
Rationale: Water has a high specific heat capacity, meaning it can
absorb a lot of heat with only a small change in temperature—a critical
factor in stabilizing the temperature of living systems.
---
4. Case Study – Density Anomaly of Water
A limnologist studies a freshwater lake and observes that ice forms on
the surface while the liquid water below remains denser until reaching
4°C.
Question: Which characteristic of water is primarily responsible for this
anomaly?
A. Its linear structure
B. Strong ionic interactions
C. The hydrogen bond network forming an open hexagonal lattice in ice
D. Its negligible polarity
ANS: C. The hydrogen bond network forming an open hexagonal
lattice in ice
Rationale: In ice, hydrogen bonds create an open, less dense hexagonal
lattice structure. As a result, water reaches maximum density at 4°C;
below this temperature, expansion occurs upon freezing.
©2025
, ---
5. Case Study – Solvent Properties of Water
A biochemist dissolves an ionic salt in water and notes that the salt
dissociates rapidly.
Question: What property of water facilitates the dissolution of ionic
compounds?
A. High viscosity
B. Low dielectric constant
C. High polarity and dielectric constant
D. Amphipathic nature
ANS: C. High polarity and dielectric constant
Rationale: Water’s polarity and remarkably high dielectric constant
(≈80 at 25°C) reduce the electrostatic attraction between ions, allowing
them to separate and be solvated.
---
6. Case Study – Autodissociation of Water
In a controlled experiment, pure water at 25°C is analyzed, and the
hydronium ion concentration is measured.
Question: What is the expected pH of pure water under these
conditions?
A. 0
B. 7
C. 14
D. 5.5
ANS: B. 7
Rationale: At 25°C, the autoionization of water yields [H⁺] = [OH⁻] ≈ 1.0
× 10⁻⁷ M, resulting in a neutral pH of approximately 7.
---
©2025
Final Assessment Review
Module 2 (Questions & Solutions)
2025
©2025
, 1. Case Study – Molecular Geometry of Water
An X‑ray diffraction study in a research lab measures the bond angle
between the hydrogen atoms in a water molecule. The measured angle is
found to be approximately 104.5°.
Question: Which of the following best explains this bond angle?
A. The linear arrangement of oxygen and hydrogen atoms
B. Sp³ hybridization of oxygen with two lone pairs causing repulsion
C. Planar trigonal geometry of the water molecule
D. Ionic bonding between hydrogen and oxygen
ANS: B. Sp³ hybridization of oxygen with two lone pairs causing
repulsion
Rationale: Oxygen in H₂O is sp³ hybridized; the two lone pairs occupy
more space than bonding pairs, forcing the H–O–H angle to decrease
from the ideal tetrahedral angle (109.5°) to about 104.5°.
---
2. Case Study – Boiling Point and Hydrogen Bonding
A researcher compares boiling points of H₂O and H₂S. Despite similar
molecular weights, water boils much higher than hydrogen sulfide.
Question: What is the primary reason for water’s high boiling point?
A. Strong ionic bonds in water
B. Extensive hydrogen bonding between water molecules
C. Greater van der Waals forces in water
D. Covalent cross-linking between water molecules
ANS: B. Extensive hydrogen bonding between water molecules
Rationale: Water molecules engage in strong hydrogen bonding, which
requires significantly more energy to break than the weaker van der
Waals interactions present in H₂S.
©2025
,---
3. Case Study – Specific Heat Capacity
In a calorimetry experiment, a student heats a sample of water and
observes that it requires a large amount of energy to raise its
temperature by 1°C.
Question: What property of water does this observation demonstrate?
A. Low heat capacity
B. High specific heat capacity
C. High thermal conductivity
D. Low thermal inertia
ANS: B. High specific heat capacity
Rationale: Water has a high specific heat capacity, meaning it can
absorb a lot of heat with only a small change in temperature—a critical
factor in stabilizing the temperature of living systems.
---
4. Case Study – Density Anomaly of Water
A limnologist studies a freshwater lake and observes that ice forms on
the surface while the liquid water below remains denser until reaching
4°C.
Question: Which characteristic of water is primarily responsible for this
anomaly?
A. Its linear structure
B. Strong ionic interactions
C. The hydrogen bond network forming an open hexagonal lattice in ice
D. Its negligible polarity
ANS: C. The hydrogen bond network forming an open hexagonal
lattice in ice
Rationale: In ice, hydrogen bonds create an open, less dense hexagonal
lattice structure. As a result, water reaches maximum density at 4°C;
below this temperature, expansion occurs upon freezing.
©2025
, ---
5. Case Study – Solvent Properties of Water
A biochemist dissolves an ionic salt in water and notes that the salt
dissociates rapidly.
Question: What property of water facilitates the dissolution of ionic
compounds?
A. High viscosity
B. Low dielectric constant
C. High polarity and dielectric constant
D. Amphipathic nature
ANS: C. High polarity and dielectric constant
Rationale: Water’s polarity and remarkably high dielectric constant
(≈80 at 25°C) reduce the electrostatic attraction between ions, allowing
them to separate and be solvated.
---
6. Case Study – Autodissociation of Water
In a controlled experiment, pure water at 25°C is analyzed, and the
hydronium ion concentration is measured.
Question: What is the expected pH of pure water under these
conditions?
A. 0
B. 7
C. 14
D. 5.5
ANS: B. 7
Rationale: At 25°C, the autoionization of water yields [H⁺] = [OH⁻] ≈ 1.0
× 10⁻⁷ M, resulting in a neutral pH of approximately 7.
---
©2025
