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

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Identify the Brønsted–Lowry acid in each case. A Brønsted–Lowry acid is a substance that can donate a proton (H⁺).

For each acid, remove one proton (H⁺) to find the conjugate base. This involves subtracting an H⁺ from the chemical formula of the acid.

For (i) HCOOH, remove an H⁺ to form the conjugate base. The resulting formula will be HCOO⁻.

For (ii) HPO₄²⁻, remove an H⁺ to form the conjugate base. The resulting formula will be PO₄³⁻.

Verify that the charge of the conjugate base is one unit more negative than the original acid, as losing a proton (H⁺) decreases the charge by one.

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Key Concepts

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

Brønsted–Lowry Acid-Base Theory

The Brønsted–Lowry theory defines acids as proton donors and bases as proton acceptors. This framework emphasizes the transfer of protons (H+) in chemical reactions, allowing for a broader understanding of acid-base behavior beyond just the presence of hydroxide ions. In this context, identifying conjugate bases involves recognizing the species formed when an acid donates a proton.

Conjugate Acid-Base Pairs

Conjugate acid-base pairs consist of two species that differ by the presence of a single proton. When an acid donates a proton, it transforms into its conjugate base, while the base that accepts the proton becomes its conjugate acid. Understanding these pairs is crucial for predicting the outcome of acid-base reactions and determining the strength of acids and bases.

Dissociation of Acids

The dissociation of acids refers to the process by which an acid releases protons into solution. For example, when formic acid (HCOOH) dissociates, it loses a proton to form its conjugate base, formate (HCOO-). Similarly, the dissociation of hydrogen phosphate (HPO4^2-) results in the formation of its conjugate base, phosphate (PO4^3-). This concept is essential for identifying conjugate bases in acid-base reactions.

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Acid-Base Dissociation Example

Related Practice

Textbook Question

The hydrogen sulfite ion 1HSO3-2 is amphiprotic. Write a balanced chemical equation showing how it acts as an acid toward water and another equation showing how it acts as a base toward water.

Textbook Question

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

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

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

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)