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Chapter 4: Problem 2

Write these reactions as proton-transfer reactions. Label which reactant is the acid and which is the base, which product is the conjugate base of the original acid, and which is the conjugate acid of the original base. In addition, write Lewis structures for each reactant and product, and use curved arrows to show the flow of electrons in each reaction. (a) \(\mathrm{CH}_{3} \mathrm{SH}+\mathrm{OH}^{-} \rightleftharpoons \mathrm{CH}_{3} \mathrm{~S}^{-}+\mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{CH}_{2}=\mathrm{O}+\mathrm{HCl} \rightleftharpoons \mathrm{CH}_{2}=\mathrm{OH}^{+}+\mathrm{Cl}^{-}\)

Short Answer

Expert verified
Question: Identify the acids, bases, conjugate acids, and conjugate bases in each reaction. Draw the Lewis structures of all reactants and products and show the flow of electrons using curved arrows. (a) Reaction: CH₃SH + OH⁻ → CH₃S⁻ + H₂O - Acid: CH₃SH - Base: OH⁻ - Conjugate Acid: H₂O - Conjugate Base: CH₃S⁻ (b) Reaction: CH₂=O + HCl → CH₂=OH⁺ + Cl⁻ - Acid: HCl - Base: CH₂=O - Conjugate Acid: CH₂=OH⁺ - Conjugate Base: Cl⁻

Step by step solution

01

(a) Identify the acids and bases in the reaction

In the given reaction, \(\mathrm{CH}_{3}\mathrm{SH}\) reacts with \(\mathrm{OH}^{-}\) to form \(\mathrm{CH}_{3}\mathrm{S}^{-}\) and \(\mathrm{H}_{2}\mathrm{O}.\) In this case, \(\mathrm{CH}_{3}\mathrm{SH}\) donates a proton, so it is the acid. \(\mathrm{OH}^{-}\) accepts the proton, so it is the base.
02

(a) Identify conjugate acid and conjugate base

The conjugate base of the original acid, \(\mathrm{CH}_{3}\mathrm{SH},\) is \(\mathrm{CH}_{3}\mathrm{S}^{-},\) and the conjugate acid of the original base, \(\mathrm{OH}^{-},\) is \(\mathrm{H}_{2}\mathrm{O}.\)
03

(a) Drawing Lewis structures for reactants and products, and showing electron flow

In this reaction, the electron flow can be shown with the following curved-arrow notation: \(\mathrm{CH}_{3}\mathrm{SH}\: (\:\bullet \:)\:\bullet\: - \:\bullet \mathrm{O}^{-}H \rightleftharpoons \mathrm{CH}_{3}\mathrm{S}^{-}\: (\:\bullet \:)\:\bullet \: + \:\bullet \mathrm{O} H_{2}\) The arrow starts at the lone pair on the oxygen atom and points to the hydrogen atom in \(\mathrm{CH}_{3}\mathrm{SH}\) to show the proton transfer.
04

(b) Identify the acids and bases in the reaction

In the given reaction, \(\mathrm{CH}_{2}=\mathrm{O}\) reacts with \(\mathrm{HCl}\) to form \(\mathrm{CH}_{2}=\mathrm{OH}^{+}\) and \(\mathrm{Cl}^{-}.\) In this case, \(\mathrm{HCl}\) donates a proton, so it is the acid. \(\mathrm{CH}_{2}=\mathrm{O}\) accepts the proton, so it is the base.
05

(b) Identify conjugate acid and conjugate base

The conjugate base of the original acid, \(\mathrm{HCl},\) is \(\mathrm{Cl}^{-},\) and the conjugate acid of the original base, \(\mathrm{CH}_{2}=\mathrm{O},\) is \(\mathrm{CH}_{2}=\mathrm{OH}^{+}.\)
06

(b) Drawing Lewis structures for reactants and products, and showing electron flow

In this reaction, the electron flow can be shown with the following curved-arrow notation: \(\mathrm{C}=\mathrm{O}\:(\:\bullet \:)\:\bullet\: +\: \mathrm{H} \cdot \mathrm{Cl} \rightleftharpoons \mathrm{C}=\mathrm{OH}^{+}\: (\:\bullet \:)\:\bullet + \: - \mathrm{Cl}\) The arrow starts at the lone pair on the oxygen atom and points to the hydrogen atom in \(\mathrm{HCl}\) to show the proton transfer.

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Most popular questions from this chapter

Answer True or False to the following statements about energy diagrams and reactions. (a) A reaction coordinate diagram is used to visualize the change in the internal energy of chemical structures that occurs during chemical reactions. (b) Thermodynamics is the study of the energies of structures that are represented by wells on reaction coordinate diagrams. (c) Kinetics is the study of the rates of chemical reactions. (d) One part of a reaction mechanism would be the understanding of which bonds break and form during a reaction. (e) Thermal reactions occur via collisions between molecules, and the more energy in those collisions the greater the rate of the reactions. (f) The enthalpy of a reaction is the sole determinant of whether it will or will not occur. (g) An exergonic reaction will always occur during the life span of the standard human being.

2,4-Pentanedione is a considerably stronger acid than acetone (Chapter 19). Write a structural formula for the conjugate base of each acid, and account for the greater stability of the conjugate base from 2,4-pentanedione. CCC(C)=O CC(=O)C=C(C)C Acetone 2,4-Pentanedione \(\mathrm{p} K_{\mathrm{a}} 22\) \(\mathrm{p} K_{\mathrm{a}} 9\)

If the \(\Delta G^{\circ}\) for a reaction is \(-4.5 \mathrm{kcal} / \mathrm{mol}\) at \(298 \mathrm{~K}\), what is the \(K_{\text {eq }}\) for this reaction? What is the change in entropy of this reaction if \(\Delta H^{\circ}=-3.2 \mathrm{kcal} / \mathrm{mol}\) ?

In acetic acid, \(\mathrm{CH}_{3} \mathrm{COOH}\), the \(\mathrm{OH}\) hydrogen is more acidic than the \(\mathrm{CH}_{3}\) hydrogens. Explain.

Write an equation for the reaction between each Lewis acid-base pair, showing electron flow by means of curved arrows. (a) \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{3} \mathrm{~B}+\mathrm{OH}^{-} \longrightarrow\) (b) \(\mathrm{CH}_{3} \mathrm{Cl}+\mathrm{AlCl}_{3} \longrightarrow\)
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