Acids, Bases, and Redox Flashcards

According to the Brønsted-Lowry theory, which of the following best describes an acid?

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.

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?

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.

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?

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).

What is the oxidation number of manganese (Mn) in the permanganate ion, MnO₄⁻?

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.

In the following redox reaction, which species acts as the oxidizing agent? 2Na(s) + Cl₂(g) → 2NaCl(s)

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.

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?

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).