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Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711당신이 사용하는 게 아니라요?교과서 변경
모든 교과서Bruice 8th EditionCh. 2 - Acids and Bases: Central to Understanding Organic Chemistry문제 39a,b
2장, 문제 39a,b

For each of the following compounds (here shown in their acidic forms), write the form that ­predominates in a solution with a pH = 5.5:
a. CH3COOH(pKa = 4.76)
b. CH3CH2N+H3 (pKa = 11.0)

검증된 단계별 안내
1
Step 1: Understand the problem. The question asks for the predominant form of each compound at a pH of 5.5. This involves determining whether the compound exists in its protonated (acidic) or deprotonated (basic) form based on the pKa values provided.
Step 2: Recall the relationship between pH, pKa, and the acid-base equilibrium. The Henderson-Hasselbalch equation is used to determine the ratio of protonated to deprotonated forms: pH = pKa + log([A-][HA]), where [A⁻] is the deprotonated form and [HA] is the protonated form.
Step 3: Analyze compound (a) CH3COOH (acetic acid). The pKa of acetic acid is 4.76. Compare the pH (5.5) to the pKa. Since pH > pKa, the solution is more basic than the acid's pKa, meaning the deprotonated form (CH3COO⁻) will predominate.
Step 4: Analyze compound (b) CH3CH2N+H3 (ethylammonium ion). The pKa of the conjugate acid is 11.0. Compare the pH (5.5) to the pKa. Since pH < pKa, the solution is more acidic than the base's pKa, meaning the protonated form (CH3CH2N+H3) will predominate.
Step 5: Summarize the results. For compound (a), the predominant form at pH 5.5 is CH3COO⁻. For compound (b), the predominant form at pH 5.5 is CH3CH2N+H3. These conclusions are based on the relative pH and pKa values.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Acid-Base Equilibrium

Acid-base equilibrium refers to the balance between the protonated (acidic) and deprotonated (basic) forms of a compound in solution. The pKa value indicates the strength of an acid; lower pKa values correspond to stronger acids. At a given pH, the predominant form of an acid or base can be determined using the Henderson-Hasselbalch equation, which relates pH, pKa, and the ratio of protonated to deprotonated species.
추천 영상:
04:00
Determining Acid/Base Equilibrium

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is a mathematical formula used to calculate the pH of a buffer solution. It is expressed as pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the deprotonated form and [HA] is the concentration of the protonated form. This equation helps predict the predominant form of a compound at a specific pH, which is essential for understanding the behavior of weak acids and bases in solution.
추천 영상:
05:02
Breaking down the different terms of the Gibbs Free Energy equation.

pH and its Relation to pKa

pH is a measure of the acidity or basicity of a solution, with lower values indicating higher acidity. The relationship between pH and pKa is crucial for determining the predominant species of an acid or base in solution. If the pH is lower than the pKa, the protonated form predominates; if the pH is higher, the deprotonated form is favored. This concept is vital for predicting the behavior of compounds like acetic acid and ammonium ion in the given question.
추천 영상:
07:45
Identifying pKa values
관련 실천
교과서 질문

For each of the following compounds (here shown in their acidic forms), write the form that ­predominates in a solution with a pH = 5.5:

c. H3O+ (pKa = −1.7)

d. HBr (pKa = −9)

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교과서 질문

Fosamax (shown on the previous page) has six acidic groups. The active form of the drug, which has lost two of its acidic protons, is shown in the box. 

(Notice that the phosphorus atom in Fosamax and the sulfur atom in [Problem 36] can be surrounded by more than eight electrons because P and S are below the second row of the periodic table.)

a. Why are the OH groups bonded to phosphorus the strongest acids of the six groups?

b. Which of the remaining four groups is the weakest acid?

1239
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교과서 질문

Using the table of pKa values given in [Appendix I] , answer the following:

d. Which is more electronegative: an sp3 oxygen or an sp2 oxygen?

e. Which compounds demonstrate that the relative electronegativities of a hybridized nitrogen atom are sp > sp2 > sp3?

1176
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교과서 질문

For each of the following compounds (here shown in their acidic forms), write the form that ­predominates in a solution with a pH = 5.5:

e. +NH4 (pKa = 9.4)

f. HC≡N (pKa = 9.1)

696
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교과서 질문

Using the table of pKa values given in [Appendix I], answer the following:

a. Which is the most acidic organic compound in the table?

b. Which is the least acidic organic compound in the table?

c. Which is the most acidic carboxylic acid in the table?

1376
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교과서 질문

For each of the following compounds (here shown in their acidic forms), write the form that ­predominates in a solution with a pH = 5.5:

g. HNO2 (pKa = 3.4)

h. HNO3 (pKa = −1.3)

703
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