GACE Chemistry 3 — Questions and Answers
Question 1: Which quantum number describes the shape of an electron's orbital?
- Principal quantum number (n)
- Angular momentum quantum number (l) (Correct answer)
- Magnetic quantum number (mₗ)
- Spin quantum number (mₛ)
Correct answer: Angular momentum quantum number (l)
The angular momentum quantum number (l) defines orbital shape: l=0 is s, l=1 is p, l=2 is d.
Question 2: A buffer solution resists changes in pH when small amounts of acid or base are added. Which combination would create an effective buffer near pH 7?
- HCl and NaCl
- NaOH and NaCl
- H₂PO₄⁻ and HPO₄²⁻ (Correct answer)
- Na₂SO₄ and H₂O
Correct answer: H₂PO₄⁻ and HPO₄²⁻
A buffer requires a weak acid and its conjugate base; H₂PO₄⁻/HPO₄²⁻ is a conjugate pair with pKa near 7.2.
Question 3: During electrolysis of molten NaCl, what forms at the cathode?
- Cl₂ gas
- Na metal (Correct answer)
- NaOH solution
- O₂ gas
Correct answer: Na metal
The cathode is the site of reduction; Na⁺ ions gain electrons to form Na metal.
Question 4: Which of the following correctly identifies a characteristic of transition metals?
- They have completely filled d subshells
- They form only +2 ions
- They often exhibit multiple oxidation states (Correct answer)
- They are all nonmagnetic
Correct answer: They often exhibit multiple oxidation states
Transition metals can lose varying numbers of d electrons, allowing them to exist in multiple oxidation states.
Question 5: What does the rate law for a reaction reveal about the reaction mechanism?
- The overall stoichiometry of the reaction
- Which step is the slowest (rate-determining) step (Correct answer)
- The total enthalpy change of the reaction
- The equilibrium constant K
Correct answer: Which step is the slowest (rate-determining) step
The rate law reflects the concentrations involved in the slowest elementary step, revealing the rate-determining step.
Question 6: Which law states that the total pressure of a gas mixture equals the sum of the partial pressures of each component gas?
- Boyle's Law
- Charles's Law
- Dalton's Law of Partial Pressures (Correct answer)
- Avogadro's Law
Correct answer: Dalton's Law of Partial Pressures
Dalton's Law states that each gas in a mixture exerts pressure independently, and total pressure is their sum.
Question 7: A substance that accepts a proton (H⁺) in a chemical reaction is classified as which of the following according to the Brønsted-Lowry theory?
- Arrhenius acid
- Brønsted-Lowry acid
- Lewis acid
- Brønsted-Lowry base (Correct answer)
Correct answer: Brønsted-Lowry base
According to Brønsted-Lowry theory, a base is any species that accepts a proton (H⁺) from another substance.
GACE Chemistry 3
Which quantum number describes the shape of an electron's orbital?