Regents Chemistry 3 — Questions and Answers
Question 1: What is the oxidation state of sulfur in H₂SO₄?
- +4
- +6 (Correct answer)
- +2
- -2
Correct answer: +6
In H₂SO₄, hydrogen is +1 (×2) and oxygen is -2 (×4), so sulfur must be +6 to balance the overall neutral charge.
Question 2: Which of the following best describes an exothermic reaction?
- Reactants absorb heat from surroundings
- Products have more energy than reactants
- Energy is released to the surroundings (Correct answer)
- Activation energy equals zero
Correct answer: Energy is released to the surroundings
Exothermic reactions release energy to the surroundings, causing the environment to feel warmer.
Question 3: Which statement correctly describes isotopes of the same element?
- Same mass number, different atomic number
- Same number of neutrons, different protons
- Same number of protons, different neutrons (Correct answer)
- Same electron configuration, different proton count
Correct answer: Same number of protons, different neutrons
Isotopes have the same number of protons (same element) but different numbers of neutrons, giving them different mass numbers.
Question 4: In a redox reaction, the substance that gains electrons is called the:
- Reducing agent
- Oxidizing agent (Correct answer)
- Catalyst
- Spectator ion
Correct answer: Oxidizing agent
The oxidizing agent gains electrons (is reduced) while causing the other substance to be oxidized.
Question 5: What is the molar mass of Ca(OH)₂?
- 57 g/mol
- 74 g/mol (Correct answer)
- 56 g/mol
- 90 g/mol
Correct answer: 74 g/mol
Ca = 40, O = 16×2 = 32, H = 1×2 = 2; total = 40 + 32 + 2 = 74 g/mol.
Question 6: Which intermolecular force is responsible for the unusually high boiling point of water?
- London dispersion forces
- Dipole-dipole interactions
- Hydrogen bonding (Correct answer)
- Ionic attractions
Correct answer: Hydrogen bonding
Hydrogen bonding between water molecules requires significantly more energy to overcome, resulting in water's abnormally high boiling point of 100°C.
Question 7: What happens to the rate of a chemical reaction when a catalyst is added?
- Rate decreases
- Rate increases (Correct answer)
- Rate is unchanged
- Reaction stops
Correct answer: Rate increases
A catalyst increases the reaction rate by providing an alternative pathway with lower activation energy, without being consumed.
Regents Chemistry 3
What is the oxidation state of sulfur in H₂SO₄?