PCAT Chemistry 2 — Questions and Answers
Question 1: Which type of intermolecular force is responsible for the unusually high boiling point of water compared to other small molecules?
- London dispersion forces
- Dipole-dipole interactions
- Hydrogen bonding (Correct answer)
- Ion-dipole forces
Correct answer: Hydrogen bonding
Water's high boiling point results from hydrogen bonding, which occurs between the partially positive hydrogen atoms and the lone pairs on oxygen atoms of neighboring molecules.
Question 2: What is the hybridization of the carbon atom in CO2?
- sp3
- sp2
- sp (Correct answer)
- sp3d
Correct answer: sp
Carbon in CO2 forms two double bonds with no lone pairs, resulting in sp hybridization and a linear molecular geometry.
Question 3: A buffer solution is most effective when the pH of the solution is:
- Equal to the pKb of the conjugate base
- Equal to the pKa of the weak acid (Correct answer)
- 2 units above the pKa
- Equal to 7.0
Correct answer: Equal to the pKa of the weak acid
A buffer works best when pH = pKa, because at this point the concentrations of the weak acid and its conjugate base are equal, providing maximum buffering capacity.
Question 4: Which quantum number describes the orientation of an orbital in space?
- Principal quantum number (n)
- Angular momentum quantum number (l)
- Magnetic quantum number (ml) (Correct answer)
- Spin quantum number (ms)
Correct answer: Magnetic quantum number (ml)
The magnetic quantum number (ml) specifies the orientation of an orbital in three-dimensional space relative to the other orbitals in the same subshell.
Question 5: In a galvanic cell, oxidation occurs at the:
- Cathode
- Anode (Correct answer)
- Salt bridge
- Electrolyte solution
Correct answer: Anode
Oxidation (loss of electrons) always occurs at the anode; in a galvanic cell, electrons flow from the anode through the external circuit to the cathode.
Question 6: Which of the following best describes an endothermic reaction?
- Products have lower energy than reactants and ΔH is negative
- Products have higher energy than reactants and ΔH is positive (Correct answer)
- The reaction releases heat to the surroundings
- The activation energy is always zero
Correct answer: Products have higher energy than reactants and ΔH is positive
In an endothermic reaction, energy is absorbed from the surroundings, so products have higher energy than reactants and ΔH > 0.
Question 7: What is the molarity of a solution made by dissolving 4.0 g of NaOH (molar mass = 40 g/mol) in enough water to make 500 mL of solution?
- 0.1 M
- 0.2 M (Correct answer)
- 0.4 M
- 0.8 M
Correct answer: 0.2 M
Moles of NaOH = 4.0 g ÷ 40 g/mol = 0.10 mol; Molarity = 0.10 mol ÷ 0.500 L = 0.20 M.
PCAT Chemistry 2
Which type of intermolecular force is responsible for the unusually high boiling point of water compared to other small molecules?