Regents Chemistry 4 — Questions and Answers
Question 1: Which gas law states that the volume of a gas at constant temperature is inversely proportional to its pressure?
- Charles's Law
- Gay-Lussac's Law
- Boyle's Law (Correct answer)
- Dalton's Law
Correct answer: Boyle's Law
Boyle's Law (P₁V₁ = P₂V₂) states that pressure and volume are inversely proportional at constant temperature.
Question 2: Which element is a metalloid (semimetal) on the periodic table?
- Sulfur
- Silicon (Correct answer)
- Sodium
- Selenium
Correct answer: Silicon
Silicon (Si) is a metalloid with properties intermediate between metals and nonmetals, widely used as a semiconductor.
Question 3: What is the correct name for the compound Fe₂O₃?
- Iron oxide
- Iron(II) oxide
- Iron(III) oxide (Correct answer)
- Diiron trioxide
Correct answer: Iron(III) oxide
In Fe₂O₃, iron has an oxidation state of +3 (since 3 oxygens at -2 = -6, balanced by 2 Fe at +3 = +6), so it is iron(III) oxide.
Question 4: 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 the shape of an orbital: l=0 is s (spherical), l=1 is p (dumbbell), l=2 is d, etc.
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 both galvanic and electrolytic cells.
Question 6: Which of the following represents a conjugate acid-base pair?
- HCl and NaOH
- H₂O and H₃O⁺
- NH₃ and NH₄⁺ (Correct answer)
- H₂SO₄ and SO₄²⁻
Correct answer: NH₃ and NH₄⁺
NH₃ and NH₄⁺ differ by exactly one proton (H⁺), making them a conjugate acid-base pair (NH₃ is the base, NH₄⁺ is its conjugate acid).
Question 7: What is the percent composition by mass of hydrogen in H₂O?
- 5.6%
- 11.1% (Correct answer)
- 16.7%
- 22.2%
Correct answer: 11.1%
H₂O has molar mass 18 g/mol; hydrogen contributes 2 g/mol, so percent = (2/18) × 100 ≈ 11.1%.
Regents Chemistry 4
Which gas law states that the volume of a gas at constant temperature is inversely proportional to its pressure?