CART - Chemistry Acceleration Readiness Acids, Bases, and Redox Questions and Answers — Questions and Answers
Question 1: According to the Brønsted-Lowry theory, which of the following best describes an acid?
- A substance that increases the hydroxide ion concentration in water.
- A substance that can accept a proton (H⁺).
- A substance that can donate a proton (H⁺). (Correct answer)
- A substance that can accept a pair of electrons.
Correct answer: A substance that can donate a proton (H⁺).
The Brønsted-Lowry theory defines an acid as a species that donates a proton (a hydrogen ion, H⁺) and a base as a species that accepts a proton. An electron pair acceptor is a Lewis acid, and a substance that increases [OH⁻] is an Arrhenius base.
Question 2: A student prepares a solution of hydrochloric acid (HCl), a strong acid, with a concentration of 0.001 M. What is the pH of this solution?
- 11
- 3 (Correct answer)
- -3
- 1
Correct answer: 3
The pH of a solution is calculated using the formula pH = -log[H⁺]. Because HCl is a strong acid, it completely dissociates in water, so the hydrogen ion concentration [H⁺] is equal to the molarity of the acid. Therefore, pH = -log(0.001) = -log(10⁻³) = 3.
Question 3: In a laboratory neutralization reaction, aqueous sulfuric acid (H₂SO₄) is reacted with aqueous potassium hydroxide (KOH). What are the two products formed in this reaction?
- Potassium hydride (KH) and sulfurous acid (H₂SO₃)
- Potassium sulfate (K₂SO₄) and water (H₂O) (Correct answer)
- Dipotassium oxide (K₂O) and hydrogen sulfide (H₂S)
- Potassium sulfite (K₂SO₃) and dihydrogen peroxide (H₂O₂)
Correct answer: Potassium sulfate (K₂SO₄) and water (H₂O)
A neutralization reaction between an acid and a base produces a salt and water. In this case, the acid (H₂SO₄) and the base (KOH) react. The cation from the base (K⁺) combines with the anion from the acid (SO₄²⁻) to form the salt potassium sulfate (K₂SO₄). The hydrogen ion from the acid (H⁺) combines with the hydroxide ion from the base (OH⁻) to form water (H₂O).
Question 4: What is the oxidation number of manganese (Mn) in the permanganate ion, MnO₄⁻?
- +7 (Correct answer)
- +8
- -1
- +4
Correct answer: +7
The sum of the oxidation numbers in a polyatomic ion must equal the charge of the ion. The charge on the permanganate ion is -1. The oxidation number of oxygen is typically -2. Let 'x' be the oxidation number of Mn. The equation is: x + 4(-2) = -1. Solving for x gives x - 8 = -1, so x = +7.
Question 5: In the following redox reaction, which species acts as the oxidizing agent? 2Na(s) + Cl₂(g) → 2NaCl(s)
- Na
- NaCl
- Cl₂ (Correct answer)
- This is not a redox reaction.
Correct answer: Cl₂
The oxidizing agent is the substance that gets reduced (gains electrons) and thereby causes the oxidation of another substance. In this reaction, elemental chlorine (Cl₂) has an oxidation number of 0 and becomes the chloride ion (Cl⁻) in NaCl, with an oxidation number of -1. Since its oxidation number decreased, Cl₂ gained electrons and was reduced, making it the oxidizing agent.
Question 6: Consider the following reversible reaction: HCO₃⁻(aq) + H₂O(l) ⇌ H₂CO₃(aq) + OH⁻(aq) Which of the following represents a Brønsted-Lowry conjugate acid-base pair?
- H₂O and OH⁻ (Correct answer)
- HCO₃⁻ and OH⁻
- H₂O and H₂CO₃
- HCO₃⁻ and H₂O
Correct answer: H₂O and OH⁻
A conjugate acid-base pair consists of two species that differ by a single proton (H⁺). In this reaction, H₂O acts as an acid by donating a proton to become its conjugate base, OH⁻. Therefore, H₂O and OH⁻ form a conjugate acid-base pair. The other pair is HCO₃⁻ (base) and H₂CO₃ (its conjugate acid).
CART - Chemistry Acceleration Readiness Acids, Bases, and Redox Questions and Answers
According to the Brønsted-Lowry theory, which of the following best describes an acid?