Ch.16 - Acid-Base Equilibria

Brown - Chemistry: The Central Science 15th Edition

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Brown 15th Edition

Ch.16 - Acid-Base Equilibria

Problem 20b

Chapter 16, Problem 20b

Give the conjugate acid of the following Brønsted–Lowry bases: (i) SO42-, (ii) CH3NH2.

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Identify the Brønsted–Lowry base in each case. A Brønsted–Lowry base is a species that can accept a proton (H⁺).

For each base, add a proton (H⁺) to form the conjugate acid. This involves increasing the hydrogen count by one and adjusting the charge accordingly.

For (i) SO₄²⁻, add H⁺ to form HSO₄⁻. The sulfate ion (SO₄²⁻) accepts a proton to become the hydrogen sulfate ion (HSO₄⁻).

For (ii) CH₃NH₂, add H⁺ to form CH₃NH₃⁺. The methylamine (CH₃NH₂) accepts a proton to become the methylammonium ion (CH₃NH₃⁺).

Verify that the resulting species have the correct charge and structure to ensure they are the conjugate acids of the given bases.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Brønsted–Lowry Theory

The Brønsted–Lowry theory defines acids as proton donors and bases as proton acceptors. This framework allows us to understand acid-base reactions in terms of the transfer of protons (H+ ions). In this context, identifying the conjugate acid of a base involves determining what species is formed when the base accepts a proton.

Conjugate Acid-Base Pairs

Conjugate acid-base pairs consist of two species that differ by the presence of a proton. When a base gains a proton, it becomes its conjugate acid, while the acid that donates the proton becomes its conjugate base. Understanding these pairs is essential for predicting the outcome of acid-base reactions and for identifying the conjugate acids of given bases.

Examples of Conjugate Acids

To find the conjugate acids of specific bases, one must consider the chemical structure of the base. For instance, when the sulfate ion (SO4^2-) accepts a proton, it becomes hydrogen sulfate (HSO4^-). Similarly, when methylamine (CH3NH2) accepts a proton, it forms methylammonium (CH3NH3+). Recognizing these transformations is key to solving the problem.

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Conjugate Acids and Bases Example

Related Practice

Textbook Question

Give the conjugate base of the following Brønsted–Lowry acids: (i) HIO3, (ii) NH4+.

Textbook Question

Give the conjugate base of the following Brønsted–Lowry acids: (i) HCOOH, (ii) HPO42-.

Textbook Question

Identify the Brønsted–Lowry acid and the Brønsted–Lowry base on the left side of each of the following equations, and also identify the conjugate acid and conjugate base of each on the right side:

(a) NH₄⁺(aq) + CN^-(aq) ⇌ HCN(aq) + NH₃(aq)

(b) (CH₃)₃N(aq) + H₂O(l) ⇌ (CH₃)₃NH⁺(aq) + OH^-(aq)

Textbook Question

Identify the Lewis acid and Lewis base among the reactants in each of the following reactions:

(a) Fe(ClO₄)₃(s) + 6 H₂O(l) ⇌ [Fe(H₂O)₆]³⁺(aq) + 3 ClO₄^-(aq)

(b) CN^-(aq) + H₂O(l) ⇌ HCN(aq) + OH^-(aq)

(d) HIO(lq) + NH₂^-(lq) ⇌ NH₃(lq) + IO^-(lq) (lq denotes liquid ammonia as solvent)

Textbook Question

Identify the Lewis acid and Lewis base in each of the following reactions:

(a) HNO₂(aq) + OH^-(aq) ⇌ NO₂^-(aq) + H₂O(l)

(b) FeBr₃(s) + Br^-(aq) ⇌ FeBr₄^-(aq)

(d) SO₂(g) + H₂O(l) ⇌ H₂SO₃(aq)

Textbook Question

Identify the Brønsted–Lowry acid and the Brønsted– Lowry base on the left side of each equation, and also identify the conjugate acid and conjugate base of each on the right side.

(a) HBrO(aq) + H₂O(l) ⇌ H₃O⁺(aq) + BrO^-(aq)

(b) HSO₄^-(aq) + HCO₃^-(aq) ⇌ SO₄^2-(aq) + H₂CO₃(aq)