PCAT Chemistry 4 — Questions and Answers
Question 1: Which functional group is present in a carboxylic acid?
- -OH only
- -C=O only
- -COOH (Correct answer)
- -COO-
Correct answer: -COOH
Carboxylic acids contain the -COOH functional group, which consists of both a carbonyl (C=O) and a hydroxyl (-OH) group bonded to the same carbon.
Question 2: In an SN2 reaction, which of the following substrates reacts fastest?
- Tertiary alkyl halide
- Secondary alkyl halide
- Primary alkyl halide (Correct answer)
- Neopentyl halide
Correct answer: Primary alkyl halide
Primary alkyl halides react fastest in SN2 reactions because they have the least steric hindrance, allowing the nucleophile easy backside attack access.
Question 3: Which of the following best describes the relationship between entropy and spontaneity in the Gibbs free energy equation?
- Reactions with negative ΔS are always spontaneous
- A positive ΔS always makes ΔG negative
- High entropy change favors spontaneity by making ΔG more negative (Correct answer)
- Entropy change has no effect on ΔG
Correct answer: High entropy change favors spontaneity by making ΔG more negative
In ΔG = ΔH - TΔS, a large positive ΔS makes the -TΔS term more negative, thereby lowering ΔG and favoring spontaneity.
Question 4: Which of the following is an example of a nucleophile?
- BF3
- AlCl3
- H+
- NH3 (Correct answer)
Correct answer: NH3
NH3 is a nucleophile because it has a lone pair of electrons that it can donate to electrophilic centers during a reaction.
Question 5: The pH of a 0.01 M solution of HCl is:
- 1
- 2 (Correct answer)
- 12
- 13
Correct answer: 2
HCl is a strong acid that fully dissociates, giving [H+] = 0.01 M = 10^-2 M, so pH = -log(10^-2) = 2.
Question 6: The Aufbau principle states that electrons:
- Cannot share quantum numbers
- Fill higher energy orbitals before lower ones
- Fill lower energy orbitals before higher ones (Correct answer)
- Always occupy orbitals with parallel spins
Correct answer: Fill lower energy orbitals before higher ones
The Aufbau principle states that electrons fill available orbitals starting with those of lowest energy, building up the electron configuration from the ground state.
Question 7: Which of the following reactions represents saponification?
- Hydrolysis of an ester in acidic conditions
- Hydrolysis of an ester in basic conditions to form a carboxylate salt and alcohol (Correct answer)
- Esterification of a carboxylic acid with an alcohol
- Oxidation of a primary alcohol to a carboxylic acid
Correct answer: Hydrolysis of an ester in basic conditions to form a carboxylate salt and alcohol
Saponification is the base-catalyzed hydrolysis of an ester, producing a carboxylate salt and alcohol, commonly used in soap-making.
PCAT Chemistry 4
Which functional group is present in a carboxylic acid?