Problem 20 - Chemistry: An Atoms-Focused Approach

Question

Compounds that do not ionize in water have been known to ionize in nonaqueous solvents. In such a solvent, what would be the conjugate acid and conjugate base of methanol, \(\mathrm{CH}_{3} \mathrm{OH}\) ?

Step-by-Step Solution

Answer

Answer: The conjugate acid of methanol is methanolium (CH3OH2+), and the conjugate base is methoxide (CH3O-).

Step 1: Understanding the Concepts of Conjugate Acid and Conjugate Base

When a Bronsted-Lowry acid loses a proton (H+), the remaining species is known as its conjugate base. Similarly, when a Bronsted-Lowry base gains a proton, the resulting species is called its conjugate acid.

Step 2: Analyzing Methanol's Chemical Structure

Examine the structure of methanol (CH3OH). Methanol contains an oxygen atom with two lone pairs and a hydrogen atom bonded to the oxygen atom. This hydrogen atom is capable of participating in acid-base reactions.

Step 3: Identifying Methanol as an Acid

When methanol acts as an acid, it donates a proton (H+) to a base. The oxygen atom in methanol becomes negatively charged because it retains the electrons from the O-H bond. When this happens, methanol turns into its conjugate base: CH3OH -> CH3O- + H+ The resulting ion, methoxide (CH3O-), has a negative charge and is more stable in nonaqueous solvents than in water.

Step 4: Identifying Methanol as a Base

When methanol acts as a base, it accepts a proton (H+) from an acid. By accepting a proton, its oxygen atom forms an O-H bond, and overall methanol gains a positive charge: CH3OH + H+ -> CH3OH2+ The resulting ion, methanolium (CH3OH2+), has a positive charge and is more stable in nonaqueous solvents than in water.

Step 5: Determining the Conjugate Acid and Conjugate Base of Methanol

Based on the ionization processes described in steps 3 and 4, the conjugate acid of methanol is methanolium (CH3OH2+) and the conjugate base of methanol is methoxide (CH3O-).