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Ch. 25 - Amines: Structure, Reactions, and Synthesis
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
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Tutti i libri di testoMullins 1st EditionCh. 25 - Amines: Structure, Reactions, and SynthesisProblema 46c
Capitolo 24, Problema 46c

Given the pKb, calculate the pKa of the conjugate acid.
(c) Chemical structure of an aniline molecule with pKb value of 9.4 displayed below it.

Guida verificata passo dopo passo
1
Step 1: Recall the relationship between pKa and pKb for a conjugate acid-base pair. The equation is: \( pKa + pKb = 14 \). This equation is derived from the ionization constant of water \( K_w \), where \( K_w = 10^{-14} \) at 25°C.
Step 2: Identify the given value in the problem. The pKb of morpholine is provided as \( 5.6 \). This corresponds to the basicity of morpholine.
Step 3: Rearrange the equation \( pKa + pKb = 14 \) to solve for pKa. The rearranged equation is: \( pKa = 14 - pKb \).
Step 4: Substitute the given pKb value into the rearranged equation. Replace \( pKb \) with \( 5.6 \) in the equation \( pKa = 14 - pKb \).
Step 5: Perform the subtraction to calculate the pKa value. The result will represent the acidity of the conjugate acid of morpholine.

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pKa and pKb Relationship

The pKa and pKb values are related through the equation pKa + pKb = 14 at 25°C. The pKa represents the acidity of a compound, while pKb indicates its basicity. For a conjugate acid-base pair, knowing one value allows the calculation of the other, which is essential for understanding the strength of acids and bases.
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Identifying pKa values

Conjugate Acids and Bases

A conjugate acid is formed when a base accepts a proton (H+), while a conjugate base is what remains after an acid donates a proton. In this context, morpholine acts as a base, and its conjugate acid is formed when it accepts a proton. Understanding this relationship is crucial for calculating pKa from pKb.
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Equilibrium constant and conjugates.

Morpholine Structure and Properties

Morpholine is a cyclic amine with a nitrogen atom in its structure, which contributes to its basic properties. The presence of the nitrogen atom allows morpholine to accept protons, making it a base. Its pKb value of 5.6 indicates its strength as a base, which is important for determining the pKa of its conjugate acid.
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