Textbook Question
Calculate the pH of the following solutions.
a. 5.00 g of HBr in 100 mL of aqueous solution
b. 1.50 g of NaOH in 50 mL of aqueous solution
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Ch. 2 - Acids and Bases; Functional Groups
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 2, Problem 9b
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.
Verified step by step guidance1
Ammonia (NH₃) can act as both an acid and a base due to its ability to donate and accept protons. As a base, ammonia accepts a proton from water, forming ammonium ion (NH₄⁺) and hydroxide ion (OH⁻). As an acid, ammonia can donate a proton to form the amide ion (NH₂⁻). In aqueous solutions, ammonia commonly acts as a base, accepting protons from water.
Water (H₂O) can serve as both an acid and a base due to its amphoteric nature. As an acid, water can donate a proton to form hydroxide ion (OH⁻). As a base, water can accept a proton to form hydronium ion (H₃O⁺). This dual ability allows water to participate in acid-base reactions in both roles.
In the table, ammonia is shown as a conjugate base of the ammonium ion (NH₄⁺), indicating its role as a base when it accepts a proton. The equilibrium reaction is: NH₄⁺ + H₂O ⇌ H₃O⁺ + NH₃.
The table also shows water as both an acid and a conjugate base. As an acid, water donates a proton to form hydroxide ion (OH⁻), and as a base, it accepts a proton to form hydronium ion (H₃O⁺). The equilibrium reactions are: H₂O + H₂O ⇌ H₃O⁺ + OH⁻.
The concept of conjugate acid-base pairs is crucial in understanding these roles. A conjugate acid is formed when a base gains a proton, and a conjugate base is formed when an acid loses a proton. This concept helps explain the dual roles of ammonia and water in acid-base chemistry.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Amphoteric Nature of Substances
Ammonia (NH3) is amphoteric, meaning it can act as both an acid and a base. As a base, it can accept a proton (H+) to form the ammonium ion (NH4+). Conversely, it can donate a proton in the presence of a stronger base, thus acting as an acid. This dual behavior is crucial for understanding its role in various chemical reactions, especially in aqueous solutions.
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Conjugate Acid-Base Pairs
In acid-base chemistry, every acid has a conjugate base and vice versa. When ammonia acts as a base, it forms its conjugate acid, the ammonium ion (NH4+). Conversely, when it acts as an acid, it donates a proton to form its conjugate base, which is the amide ion (NH2-). Understanding these pairs helps clarify the equilibrium between acids and bases in solution.
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Water as an Acid and Base
Water (H2O) is also amphoteric and can act as both an acid and a base. It can donate a proton to form the hydroxide ion (OH-) when acting as an acid, or accept a proton to form the hydronium ion (H3O+) when acting as a base. This property is fundamental in many chemical reactions, particularly in aqueous environments, where water is often the solvent.
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Related Practice
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.
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.
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Textbook Question
Circle the member of each pair that is more soluble in water.
a. CH3CH2OCH2CH3 or CH3CH2CH2CH2CH3
b. CH3CH2OCH2CH3 or CH3CH2CH2OH
c. CH3CH2NHCH3 or CH3CH2CH2CH3
d. CH3CH2OH or CH3CH2CH2CH2OH
e.
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Textbook Question
For each pair of compounds, circle the compound you expect to have the higher boiling point. Explain your reasoning.
(d) HOCH2—(CH2)4—CH2OH or (CH3)3CCH(OH)CH3
(e) (CH3CH2CH2)2NH or (CH3CH2)3N
(f)
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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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