CHM2046L Final Exam UF Spring Study Guide
| University of Florida Chemistry 2 Lab
Review & Practice
Section 1: Kinetics (Iodine Clock Reaction)
1. In the iodine clock reaction, the rate law is determined to be Rate = k[I⁻][H₂O₂]. If
doubling [I⁻] doubles the rate, and doubling [H₂O₂] doubles the rate, what is the overall
order?
A) 0
B) 1
C) 2
D) 3
Answer: C
Rationale: Overall order = 1 + 1 = 2.
2. Which reagent is used as the "clock" indicator in the iodine clock reaction?
A) Phenolphthalein
B) Thiosulfate (S₂O₃²⁻)
C) Starch
D) Potassium iodate
Answer: C
Rationale: Starch forms a blue-black complex with I₂, but thiosulfate delays the color change
until all thiosulfate is consumed.
3. If the activation energy of a reaction is 50 kJ/mol and the temperature increases from
25°C to 35°C, what happens to the rate constant (approximately)?
A) Doubles
B) Triples
C) Increases by ~50%
D) Remains the same
Answer: A
Rationale: Using the Arrhenius equation, a 10°C increase near room temperature roughly
doubles k.
,4. In the iodine clock lab, why do we measure the time for the blue color to appear?
A) To measure equilibrium constant
B) To measure initial rate indirectly
C) To find the pH
D) To identify the catalyst
Answer: B
Rationale: Time to color change is inversely proportional to initial rate.
5. Which of the following would increase the rate of the iodine clock reaction?
A) Adding more water
B) Decreasing temperature
C) Adding a catalyst
D) Removing some KI
Answer: C
Rationale: Catalysts lower activation energy, increasing rate.
Section 2: Chemical Equilibrium (FeSCN²⁺)
6. In the Fe³⁺ + SCN⁻ ⇌ FeSCN²⁺ equilibrium lab, the equilibrium constant is determined
using:
A) pH meter
B) Spectrophotometry
C) Conductivity
D) Titration
Answer: B
Rationale: FeSCN²⁺ is red; absorbance at ~470 nm measures concentration.
7. If you add more Fe³⁺ to the equilibrium mixture, the FeSCN²⁺ concentration will:
A) Increase
B) Decrease
C) Stay the same
D) Become zero
Answer: A
Rationale: Le Châtelier’s principle: adding reactant shifts right.
8. A student measures absorbance of a standard solution of FeSCN²⁺ as 0.450. If the Beer’s
Law slope is 5000 M⁻¹, what is the concentration?
A) 9.0 × 10⁻⁵ M
B) 1.11 × 10⁻⁴ M
, C) 4.5 × 10⁻⁴ M
D) 0.450 M
Answer: A
Rationale: A = εbc, so c = A/(εb) = 0. = 9.0×10⁻⁵ M.
9. In preparing the calibration curve, what is held constant?
A) Wavelength
B) Temperature
C) Path length
D) All of the above
Answer: D
Rationale: Calibration requires fixed λ, T, and cuvette path length.
10. If the equilibrium constant Kc is very small (<0.001), the reaction favors:
A) Products
B) Reactants
C) No change
D) Completion
Answer: B
Rationale: Small K means equilibrium lies far left.
Section 3: Acid-Base Titrations & pH
11. In the titration of a weak acid with a strong base, the equivalence point pH is:
A) 7
B) <7
C) >7
D) Depends on concentration
Answer: C
Rationale: Conjugate base of weak acid hydrolyzes to produce OH⁻.
12. Which indicator would be best for a weak acid (Ka=1×10⁻⁵) titrated with NaOH?
A) Methyl orange (pKa=3.4)
B) Bromothymol blue (pKa=7.1)
C) Phenolphthalein (pKa=9.4)
D) Thymol blue (pKa=1.7)
Answer: C
Rationale: Equivalence point pH ≈ 8-10; phenolphthalein changes in that range.
| University of Florida Chemistry 2 Lab
Review & Practice
Section 1: Kinetics (Iodine Clock Reaction)
1. In the iodine clock reaction, the rate law is determined to be Rate = k[I⁻][H₂O₂]. If
doubling [I⁻] doubles the rate, and doubling [H₂O₂] doubles the rate, what is the overall
order?
A) 0
B) 1
C) 2
D) 3
Answer: C
Rationale: Overall order = 1 + 1 = 2.
2. Which reagent is used as the "clock" indicator in the iodine clock reaction?
A) Phenolphthalein
B) Thiosulfate (S₂O₃²⁻)
C) Starch
D) Potassium iodate
Answer: C
Rationale: Starch forms a blue-black complex with I₂, but thiosulfate delays the color change
until all thiosulfate is consumed.
3. If the activation energy of a reaction is 50 kJ/mol and the temperature increases from
25°C to 35°C, what happens to the rate constant (approximately)?
A) Doubles
B) Triples
C) Increases by ~50%
D) Remains the same
Answer: A
Rationale: Using the Arrhenius equation, a 10°C increase near room temperature roughly
doubles k.
,4. In the iodine clock lab, why do we measure the time for the blue color to appear?
A) To measure equilibrium constant
B) To measure initial rate indirectly
C) To find the pH
D) To identify the catalyst
Answer: B
Rationale: Time to color change is inversely proportional to initial rate.
5. Which of the following would increase the rate of the iodine clock reaction?
A) Adding more water
B) Decreasing temperature
C) Adding a catalyst
D) Removing some KI
Answer: C
Rationale: Catalysts lower activation energy, increasing rate.
Section 2: Chemical Equilibrium (FeSCN²⁺)
6. In the Fe³⁺ + SCN⁻ ⇌ FeSCN²⁺ equilibrium lab, the equilibrium constant is determined
using:
A) pH meter
B) Spectrophotometry
C) Conductivity
D) Titration
Answer: B
Rationale: FeSCN²⁺ is red; absorbance at ~470 nm measures concentration.
7. If you add more Fe³⁺ to the equilibrium mixture, the FeSCN²⁺ concentration will:
A) Increase
B) Decrease
C) Stay the same
D) Become zero
Answer: A
Rationale: Le Châtelier’s principle: adding reactant shifts right.
8. A student measures absorbance of a standard solution of FeSCN²⁺ as 0.450. If the Beer’s
Law slope is 5000 M⁻¹, what is the concentration?
A) 9.0 × 10⁻⁵ M
B) 1.11 × 10⁻⁴ M
, C) 4.5 × 10⁻⁴ M
D) 0.450 M
Answer: A
Rationale: A = εbc, so c = A/(εb) = 0. = 9.0×10⁻⁵ M.
9. In preparing the calibration curve, what is held constant?
A) Wavelength
B) Temperature
C) Path length
D) All of the above
Answer: D
Rationale: Calibration requires fixed λ, T, and cuvette path length.
10. If the equilibrium constant Kc is very small (<0.001), the reaction favors:
A) Products
B) Reactants
C) No change
D) Completion
Answer: B
Rationale: Small K means equilibrium lies far left.
Section 3: Acid-Base Titrations & pH
11. In the titration of a weak acid with a strong base, the equivalence point pH is:
A) 7
B) <7
C) >7
D) Depends on concentration
Answer: C
Rationale: Conjugate base of weak acid hydrolyzes to produce OH⁻.
12. Which indicator would be best for a weak acid (Ka=1×10⁻⁵) titrated with NaOH?
A) Methyl orange (pKa=3.4)
B) Bromothymol blue (pKa=7.1)
C) Phenolphthalein (pKa=9.4)
D) Thymol blue (pKa=1.7)
Answer: C
Rationale: Equivalence point pH ≈ 8-10; phenolphthalein changes in that range.
