R3.1 - Proton Transfer Reactions

What is the definition of a Bronsted-Lowry acid?

• A substance that accepts a proton

• A substance that donates a proton

• A substance that donates electrons

• A substance that accepts electrons

Answer explanation

A Bronsted-Lowry acid is defined as a substance that donates a proton (H+). This distinguishes it from bases, which accept protons. Therefore, the correct answer is 'A substance that donates a proton'.

What is the conjugate base of HCl?

• Cl⁻

• H₂O

• OH⁻

• H₃O⁺

Answer explanation

The conjugate base of an acid is what remains after the acid donates a proton. HCl donates a proton (H⁺) to become Cl⁻, making Cl⁻ the correct conjugate base.

In the reaction between ammonia (NH₃) and water, which species acts as the Bronsted-Lowry base?

• NH₃

• H₂O

• NH₄⁺

• OH⁻

Answer explanation

In the reaction between NH₃ and water, NH₃ accepts a proton (H⁺) from water, making it the Bronsted-Lowry base. Water acts as the acid by donating the proton, while NH₄⁺ and OH⁻ are products of the reaction.

Which of the following substances is amphoteric?

• NaOH

• H₂SO₄

• HCl

• H₂O

Answer explanation

H₂O is amphoteric because it can act as both an acid and a base. It can donate a proton (H⁺) to form OH⁻ or accept a proton to form H₃O⁺, unlike NaOH, H₂SO₄, and HCl, which are strictly bases or acids.

What is the conjugate acid of NH₃?

• NH₄⁺

• OH⁻

• H₃O⁺

• H₂O

Answer explanation

The conjugate acid of a base is formed when the base accepts a proton (H⁺). NH₃ (ammonia) accepts a proton to become NH₄⁺ (ammonium), making NH₄⁺ the correct answer.

Which of the following is a strong acid?

• CH₃COOH

• H₂CO₃

• HCl

• H₂O

Answer explanation

HCl (hydrochloric acid) is a strong acid that completely dissociates in water, making it highly effective in increasing hydrogen ion concentration. In contrast, CH₃COOH (acetic acid) and H₂CO₃ (carbonic acid) are weak acids.

Which of the following is a weak base?

• NaOH

• NH₃

• KOH

• H₂SO₄

What is the pH of a neutral solution at 25°C?

• 0

• 7

• 14

• 10

In the reaction HCl + H₂O → H₃O⁺ + Cl⁻, what is the role of H₂O?

• Acid

• Base

• Salt

• Buffer

What is the pH of a solution with a hydrogen ion concentration of 1 × 10⁻³ M?

• 3

• 7

• 10

• 1

Answer explanation

The pH is calculated using the formula pH = -log[H+]. For a hydrogen ion concentration of 1 × 10⁻³ M, pH = -log(1 × 10⁻³) = 3. Therefore, the correct answer is 3.