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Ch. 2 - Acids and Bases; Functional Groups
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh. 2 - Acids and Bases; Functional GroupsProblem 11a
Chapter 2, Problem 11a

Ethanol, methylamine, and acetic acid are all amphoteric, reacting as either acids or bases depending on the conditions.

a. Rank ethanol, methylamine, and acetic acid in decreasing order of acidity. In each case, show the equation for the reaction with a generic base (B:−) to give the conjugate base.

Verified step by step guidance
1
Identify the functional groups in each compound: Ethanol (CH3CH2OH) contains a hydroxyl group, methylamine (CH3NH2) contains an amino group, and acetic acid (CH3COOH) contains a carboxylic acid group.
Understand the acidity of each functional group: Carboxylic acids are generally more acidic than alcohols and amines due to the resonance stabilization of their conjugate base. Alcohols are more acidic than amines because the oxygen in the hydroxyl group is more electronegative than the nitrogen in the amino group.
Rank the compounds based on acidity: Acetic acid is the most acidic due to the carboxylic acid group, followed by ethanol with the hydroxyl group, and methylamine is the least acidic with the amino group.
Write the reaction of each compound with a generic base (B:−) to form the conjugate base: For ethanol, CH3CH2OH + B:− → CH3CH2O− + HB. For methylamine, CH3NH2 + B:− → CH3NH− + HB. For acetic acid, CH3COOH + B:− → CH3COO− + HB.
Conclude the ranking: The decreasing order of acidity is acetic acid > ethanol > methylamine, based on the ability of each compound to donate a proton and the stability of the resulting conjugate base.

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Key Concepts

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

Acidity and Conjugate Bases

Acidity refers to the ability of a substance to donate protons (H+) in a reaction. The strength of an acid is often measured by its dissociation constant (Ka). When an acid donates a proton, it forms a conjugate base, which is the species that remains after the acid has lost a proton. Understanding the relationship between acids and their conjugate bases is crucial for ranking their acidity.
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Amphoteric Compounds

Amphoteric compounds can act as both acids and bases depending on the surrounding conditions. For example, ethanol can donate a proton to act as an acid or accept a proton to function as a base. Recognizing the amphoteric nature of ethanol, methylamine, and acetic acid is essential for understanding their behavior in acid-base reactions and for determining their relative acidity.
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Structure-Activity Relationship

The structure of a molecule significantly influences its acidity. Factors such as electronegativity, resonance, and steric effects play a role in determining how easily a compound can donate a proton. For instance, acetic acid has a carboxylic acid group that stabilizes the negative charge of its conjugate base through resonance, making it a stronger acid compared to ethanol and methylamine, which lack such stabilization.
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Related Practice
Textbook Question

Ammonia appears in [TABLE 2-2 ] as both an acid and a conjugate base. a. Explain how ammonia can act as both an acid and a base. Which of these roles does it commonly fill in aqueous solutions?

b. Show how water can serve as both an acid and a base.

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Textbook Question

Ammonia appears in [TABLE 2-2] as both an acid and a conjugate base.

d. Show how methanol (CH3OH) can serve as both an acid and a base. Write an equation for the reaction of methanol with sulfuric acid.

Textbook Question

Ethanol, methylamine, and acetic acid are all amphoteric, reacting as either acids or bases depending on the conditions.

b. Rank ethanol, methylamine, and acetic acid in decreasing order of basicity. In each case, show the equation for the reaction with a generic acid (HA) to give the conjugate acid.

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Textbook Question

For each of the following reactions, suggest which solvent(s) would be compatible with the acids and bases involved. (We will ignore any other possible reactions for now.) Your choices of solvents are pentane, diethyl ether, ethanol, water, and ammonia. Refer to Appendix 4 for any needed values of pKa, or estimate them. 

c.

d.

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Textbook Question

Write equations for the following acid–base reactions. Use the information in Table 2-2 or Appendix 4 to predict whether the equilibrium will favor the reactants or the products.

a. HCOOH + –CN

b. CH3COO– + CH3OH

c. (CH3)2CHOH + NaNH2

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Textbook Question

For each of the following reactions, suggest which solvent(s) would be compatible with the acids and bases involved. (We will ignore any other possible reactions for now.) Your choices of solvents are pentane, diethyl ether, ethanol, water, and ammonia. Refer to Appendix 4 for any needed values of pKa, or estimate them.

a. CH3Li + H—C≡C—H → CH4 + H—C≡CLi

b. CH3Li + (CH3)3C—OH → CH4 + (CH3)3C—OLi

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