OAT General Chemistry 3 — Questions and Answers
Question 1: The Henderson-Hasselbalch equation is used to calculate:
- Solubility product constants
- pH of a buffer solution (Correct answer)
- Standard cell potential
- Activation energy of a reaction
Correct answer: pH of a buffer solution
The Henderson-Hasselbalch equation (pH = pKa + log([A⁻]/[HA])) calculates the pH of buffer solutions.
Question 2: Which of the following represents an endothermic process?
- Combustion of methane
- Freezing of water
- Condensation of steam
- Dissolution of ammonium nitrate in water (Correct answer)
Correct answer: Dissolution of ammonium nitrate in water
Dissolution of NH4NO3 in water absorbs heat (feels cold), making it an endothermic process.
Question 3: What is the molarity of a solution made by dissolving 4.0 g of NaOH (MW = 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 = 4.0/40 = 0.1 mol; Molarity = 0.1 mol / 0.5 L = 0.2 M.
Question 4: Which of the following is a Lewis acid?
- NH3
- H2O
- OH⁻
- BF3 (Correct answer)
Correct answer: BF3
BF3 is a Lewis acid because it is an electron pair acceptor (boron has an empty p orbital).
Question 5: In an electrochemical cell, oxidation occurs at the:
- Cathode
- Anode (Correct answer)
- Salt bridge
- Electrolyte
Correct answer: Anode
Oxidation (loss of electrons) always occurs at the anode in any electrochemical cell.
Question 6: Which gas law states that the pressure of a gas is directly proportional to its absolute temperature at constant volume?
- Boyle's Law
- Charles's Law
- Gay-Lussac's Law (Correct answer)
- Avogadro's Law
Correct answer: Gay-Lussac's Law
Gay-Lussac's Law states P ∝ T (at constant volume and moles of gas).
Question 7: The rate law for a reaction is rate = k[A]²[B]. If [A] is doubled while [B] is held constant, the rate will:
- Double
- Triple
- Quadruple (Correct answer)
- Increase by a factor of 8
Correct answer: Quadruple
Since the reaction is second order in A, doubling [A] increases the rate by 2² = 4 (quadruples).
OAT General Chemistry 3
The Henderson-Hasselbalch equation is used to calculate: