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Ch. 4 - Acids and Bases: Electron Flow
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
Chapter 3, Problem 14b

Using the convention that the acid and base are on the left side of the chemical equation, label the acid, base, conjugate acid, and conjugate base in the following reactions.
(b)

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1
Step 1: Identify the acid and base on the left side of the equation. The acid is the species that donates a proton (H⁺), and the base is the species that accepts the proton. In this reaction, HBr is the acid because it donates a proton, and the alkyne (CH≡CH) is the base because it accepts the proton.
Step 2: Determine the conjugate acid and conjugate base on the right side of the equation. The conjugate acid is the species formed when the base gains a proton, and the conjugate base is the species formed when the acid loses a proton. Here, the conjugate acid is the carbocation (CH₂=CH⁺), and the conjugate base is the bromide ion (Br⁻).
Step 3: Label the acid, base, conjugate acid, and conjugate base in the chemical equation. On the left side, HBr is labeled as the acid, and CH≡CH is labeled as the base. On the right side, CH₂=CH⁺ is labeled as the conjugate acid, and Br⁻ is labeled as the conjugate base.
Step 4: Understand the proton transfer mechanism. The proton (H⁺) from HBr is transferred to the alkyne (CH≡CH), resulting in the formation of the carbocation (CH₂=CH⁺) and bromide ion (Br⁻). This is a typical acid-base reaction.
Step 5: Verify the reaction follows the Bronsted-Lowry acid-base theory. The acid (HBr) donates a proton, and the base (CH≡CH) accepts it, forming the conjugate acid (CH₂=CH⁺) and conjugate base (Br⁻). This confirms the labeling is consistent with the theory.

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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. In a chemical reaction, the acid donates a hydrogen ion (H+) to the base, which accepts it. This theory helps in identifying the roles of substances in acid-base reactions, making it essential for labeling acids and bases in chemical equations.
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Conjugate Acid-Base Pairs

A conjugate acid-base pair consists of two species that differ by the presence of a single proton. When an acid donates a proton, it forms its conjugate base, while the base that accepts the proton becomes its conjugate acid. Understanding these pairs is crucial for identifying the products of acid-base reactions and labeling them correctly.
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Chemical Equation Representation

Chemical equations represent the reactants and products of a reaction, showing how substances interact. In the context of acid-base reactions, the left side typically contains the acid and base, while the right side shows the conjugate acid and conjugate base. Familiarity with this representation is vital for accurately labeling the components in the given reactions.
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