Question

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

Question: In the proton-transfer reactions given below, identify the acid, base, conjugate acid, and conjugate base for each reaction. (a) \(\mathrm{CH}_{3}\mathrm{SH}+\mathrm{OH}^{-}\rightleftharpoons\mathrm{CH}_{3}\mathrm{S}^{-}+\mathrm{H}_{2}\mathrm{O}\) (b) \(\mathrm{CH}_{2}=\mathrm{O}+\mathrm{HCl}\rightleftharpoons\mathrm{CH}_{2}=\mathrm{OH}^{+}+\mathrm{Cl}^{-}\) Answer: (a) Acid: \(\mathrm{CH}_{3}\mathrm{SH}\), Base: \(\mathrm{OH}^{-}\), Conjugate Acid: \(\mathrm{H}_{2}\mathrm{O}\), Conjugate Base: \(\mathrm{CH}_{3}\mathrm{S}^{-}\). (b) Acid: \(\mathrm{HCl}\), Base: \(\mathrm{CH}_{2}=\mathrm{O}\), Conjugate Acid: \(\mathrm{CH}_{2}=\mathrm{OH}^{+}\), Conjugate Base: \(\mathrm{Cl}^{-}\).

Step-by-step solution

Identify Acid, Base, Conjugate Acid, and Conjugate Base

For the reaction \(\mathrm{CH}_{3} \mathrm{SH}+\mathrm{OH}^{-} \rightleftharpoons \mathrm{CH}_{3} \mathrm{S}^{-}+\mathrm{H}_{2} \mathrm{O}\), we identify the reactants and products as follows: - Acid: \(\mathrm{CH}_{3}\mathrm{SH}\) (donates a proton) - Base: \(\mathrm{OH}^{-}\) (accepts a proton) - Conjugate Base: \(\mathrm{CH}_{3}\mathrm{S}^{-}\) (after donating a proton) - Conjugate Acid: \(\mathrm{H}_{2}\mathrm{O}\) (after accepting a proton)

Write Lewis Structures

Here are the Lewis structures of each reactant and product: - \(\mathrm{CH}_{3}\mathrm{SH}\): H-C-S-H with a lone pair of electrons on the sulfur atom. - \(\mathrm{OH}^{-}\): O-H with three lone pairs of electrons on the oxygen atom and a negative charge. - \(\mathrm{CH}_{3}\mathrm{S}^{-}\): H-C-S with two lone pairs of electrons on the sulfur atom and a negative charge. - \(\mathrm{H}_{2}\mathrm{O}\): H-O-H with two lone pairs of electrons on the oxygen atom.

Use Curved Arrows to Show Electron Flow

The flow of electrons in this reaction can be represented by a curved arrow originating from a lone pair of electrons on the \(\mathrm{OH}^{-}\) molecule's oxygen atom and pointing toward the hydrogen atom of the \(\mathrm{CH}_{3}\mathrm{SH}\) molecule. This arrow represents the transfer of a proton from the acid to the base. (b)

Identify Acid, Base, Conjugate Acid, and Conjugate Base

For the reaction \(\mathrm{CH}_{2}=\mathrm{O}+\mathrm{HCl} \rightleftharpoons \mathrm{CH}_{2}=\mathrm{OH}^{+}+\mathrm{Cl}^{-}\), we identify the reactants and products as follows: - Acid: \(\mathrm{HCl}\) (donates a proton) - Base: \(\mathrm{CH}_{2}=\mathrm{O}\) (accepts a proton) - Conjugate Base: \(\mathrm{Cl}^{-}\) (after donating a proton) - Conjugate Acid: \(\mathrm{CH}_{2}=\mathrm{OH}^{+}\) (after accepting a proton)

Write Lewis Structures

Here are the Lewis structures of each reactant and product: - \(\mathrm{CH}_{2}=\mathrm{O}\): H-C=O-H with two lone pairs of electrons on the oxygen atom. - \(\mathrm{HCl}\): H-Cl with three lone pairs of electrons on the chlorine atom. - \(\mathrm{CH}_{2}=\mathrm{OH}^{+}\): H-C=O+-H with one lone pair of electrons on the oxygen atom and a positive charge. - \(\mathrm{Cl}^{-}\): Cl with three lone pairs of electrons and a negative charge.

Use Curved Arrows to Show Electron Flow

The flow of electrons in this reaction can be represented by a curved arrow originating from a lone pair of electrons on the \(\mathrm{CH}_{2}=\mathrm{O}\) molecule's oxygen atom and pointing toward the hydrogen atom of the \(\mathrm{HCl}\) molecule. This arrow represents the transfer of a proton from the acid to the base.