,CHEM 210 Exam 2 | Biochemistry Exam Q&A
| Portage Learning
1. What is the molecular shape of a water molecule?
A) Linear
B) Trigonal planar
C) Bent
D) Tetrahedral
Correct Answer: Bent
Rationale: Water has a bent molecular geometry because the oxygen atom has two
lone pairs of electrons that repel the bonding pairs, pushing the hydrogen atoms closer
together. The bond angle is approximately 104.5 degrees, distinguishing it from linear or
tetrahedral arrangements.
2. The bond angle in a water molecule is approximately:
A) 109.5 degrees
B) 120 degrees
C) 90 degrees
D) 104.5 degrees
Correct Answer: 104.5 degrees
,Rationale: The bond angle in water is 104.5 degrees, which results from the bent
shape caused by the two lone pairs of electrons on the oxygen atom. This angle is less
than the tetrahedral angle of 109.5 degrees because lone pair-bonding pair repulsion is
stronger than bonding pair-bonding pair repulsion.
3. Which property of water is primarily responsible for its ability to dissolve many ionic
and polar substances?
A) High molecular mass
B) Low density
C) Polarity
D) Nonpolar covalent bonding
Correct Answer: Polarity
Rationale: Water has an uneven distribution of electron density because oxygen is
more electronegative than hydrogen. This polarity allows water molecules to interact
favorably with ions and other polar molecules, effectively dissolving them.
4. Which of the following best defines autoionization of water?
A) The process of a substance dissolving in water
B) The formation of a hydrogen bond
C) The ability of water to react with itself to form ions
D) The separation of a compound into its constituent elements
Correct Answer: The ability of water to react with itself to form ions
, Rationale: Autoionization is the ability of water to react with itself to form hydronium
(H₃O⁺) and hydroxide (OH⁻) ions. This process is essential for understanding pH and
acid-base chemistry in aqueous solutions.
5. What is the value of the autoionization constant of water (Kw) at 25°C?
A) 1.0 × 10⁻⁷
B) 1.0 × 10⁻¹⁴
C) 1.0 × 10⁷
D) 1.0 × 10¹⁴
Correct Answer: 1.0 × 10⁻¹⁴
Rationale: The autoionization constant for water, Kw, is 1.0 × 10⁻¹⁴ at 25°C. This
constant is the product of the concentrations of H⁺ and OH⁻ ions: Kw = [H⁺][OH⁻].
6. What is the hydrogen ion concentration [H⁺] of a solution with a pH of 5.0?
A) 1.0 × 10⁵ M
B) 1.0 × 10⁻⁵ M
C) 1.0 × 10⁻⁹ M
D) 1.0 × 10⁹ M
Correct Answer: 1.0 × 10⁻⁵ M
| Portage Learning
1. What is the molecular shape of a water molecule?
A) Linear
B) Trigonal planar
C) Bent
D) Tetrahedral
Correct Answer: Bent
Rationale: Water has a bent molecular geometry because the oxygen atom has two
lone pairs of electrons that repel the bonding pairs, pushing the hydrogen atoms closer
together. The bond angle is approximately 104.5 degrees, distinguishing it from linear or
tetrahedral arrangements.
2. The bond angle in a water molecule is approximately:
A) 109.5 degrees
B) 120 degrees
C) 90 degrees
D) 104.5 degrees
Correct Answer: 104.5 degrees
,Rationale: The bond angle in water is 104.5 degrees, which results from the bent
shape caused by the two lone pairs of electrons on the oxygen atom. This angle is less
than the tetrahedral angle of 109.5 degrees because lone pair-bonding pair repulsion is
stronger than bonding pair-bonding pair repulsion.
3. Which property of water is primarily responsible for its ability to dissolve many ionic
and polar substances?
A) High molecular mass
B) Low density
C) Polarity
D) Nonpolar covalent bonding
Correct Answer: Polarity
Rationale: Water has an uneven distribution of electron density because oxygen is
more electronegative than hydrogen. This polarity allows water molecules to interact
favorably with ions and other polar molecules, effectively dissolving them.
4. Which of the following best defines autoionization of water?
A) The process of a substance dissolving in water
B) The formation of a hydrogen bond
C) The ability of water to react with itself to form ions
D) The separation of a compound into its constituent elements
Correct Answer: The ability of water to react with itself to form ions
, Rationale: Autoionization is the ability of water to react with itself to form hydronium
(H₃O⁺) and hydroxide (OH⁻) ions. This process is essential for understanding pH and
acid-base chemistry in aqueous solutions.
5. What is the value of the autoionization constant of water (Kw) at 25°C?
A) 1.0 × 10⁻⁷
B) 1.0 × 10⁻¹⁴
C) 1.0 × 10⁷
D) 1.0 × 10¹⁴
Correct Answer: 1.0 × 10⁻¹⁴
Rationale: The autoionization constant for water, Kw, is 1.0 × 10⁻¹⁴ at 25°C. This
constant is the product of the concentrations of H⁺ and OH⁻ ions: Kw = [H⁺][OH⁻].
6. What is the hydrogen ion concentration [H⁺] of a solution with a pH of 5.0?
A) 1.0 × 10⁵ M
B) 1.0 × 10⁻⁵ M
C) 1.0 × 10⁻⁹ M
D) 1.0 × 10⁹ M
Correct Answer: 1.0 × 10⁻⁵ M
