OAT General Chemistry Principles 3 — Questions and Answers
Question 1: Which of the following solutions has the lowest freezing point? (Assume complete dissociation for electrolytes.)
- 1 m glucose
- 1 m NaCl
- 1 m CaCl2 (Correct answer)
- 1 m sucrose
Correct answer: 1 m CaCl2
CaCl2 dissociates into 3 ions (1 Ca²⁺ + 2 Cl⁻), giving the highest van't Hoff factor and the greatest freezing point depression.
Question 2: According to Le Chatelier's principle, increasing pressure on the equilibrium N2(g) + 3H2(g) ⇌ 2NH3(g) will:
- Shift equilibrium to the left
- Shift equilibrium to the right (Correct answer)
- Have no effect
- Decrease the value of K
Correct answer: Shift equilibrium to the right
Increasing pressure favors the side with fewer moles of gas; the product side has 2 moles versus 4 moles on the reactant side.
Question 3: The electron configuration of Fe²⁺ is:
- [Ar] 3d6 4s2
- [Ar] 3d6 (Correct answer)
- [Ar] 3d4
- [Ar] 3d5 4s1
Correct answer: [Ar] 3d6
Iron (Fe) is [Ar] 3d6 4s2; losing 2 electrons first removes the 4s electrons, giving Fe²⁺ = [Ar] 3d6.
Question 4: A reaction has ΔH = +50 kJ/mol and ΔS = +100 J/(mol·K). At what temperature does the reaction become spontaneous?
- Below 500 K
- Above 500 K (Correct answer)
- At all temperatures
- Never spontaneous
Correct answer: Above 500 K
Setting ΔG = ΔH − TΔS = 0, T = ΔH/ΔS = 50,000 J / 100 J/K = 500 K; spontaneous above 500 K.
Question 5: Which type of isomers are non-superimposable mirror images of each other?
- Constitutional isomers
- Diastereomers
- Enantiomers (Correct answer)
- Conformational isomers
Correct answer: Enantiomers
Enantiomers are non-superimposable mirror images that differ only in the arrangement of groups around a chiral center.
Question 6: In the reaction 2H2O2 → 2H2O + O2, hydrogen peroxide acts as:
- Only a reducing agent
- Only an oxidizing agent
- Both oxidizing and reducing agent (Correct answer)
- Neither oxidizing nor reducing agent
Correct answer: Both oxidizing and reducing agent
H2O2 undergoes disproportionation: one molecule is oxidized (O: −1→0 in O2) and another is reduced (O: −1→−2 in H2O).
Question 7: What is the pH of a 0.01 M HCl solution?
- 1
- 2 (Correct answer)
- 7
- 12
Correct answer: 2
HCl is a strong acid that fully dissociates; [H⁺] = 0.01 M = 10⁻² M, so pH = −log(10⁻²) = 2.
OAT General Chemistry Principles 3
Which of the following solutions has the lowest freezing point? (Assume complete dissociation for electrolytes.)