Question

When methanol, \(\mathrm{CH}_{3} \mathrm{OH}\), is dissolved in water, a nonconducting solution results. When acetic acid, \(\mathrm{CH}_{3} \mathrm{COOH}\), dissolves in water, the solution is weakly conducting and acidic in nature. Describe what happens upon dissolution in the two cases, and account for the different results.

Short answer

When methanol (CH₃OH) is dissolved in water, it forms hydrogen bonds with water molecules but does not release ions, resulting in a nonconducting solution. On the other hand, when acetic acid (CH₃COOH) is dissolved in water, it undergoes weak ionization, donating protons to water molecules and forming hydronium ions (H₃O⁺) and acetate ions (CH₃COO⁻). This produces a weakly conducting and acidic solution due to the presence of ions. The differences in conductivity and acidity can be attributed to the differences in ionization properties of methanol and acetic acid when dissolved in water.

Step-by-step solution

1. Dissolution of Methanol

When methanol (CH₃OH) is dissolved in water, it interacts with water molecules through hydrogen bonding. Since methanol is a covalent compound, there is no release of ions (i.e., charged particles) in the solution. As a result, the methanol-water mixture remains nonconducting, as there are no freely mobile ions present to carry an electric charge.

2. Dissolution of Acetic Acid

When acetic acid (CH₃COOH) is dissolved in water, it undergoes a weak ionization process, in which a small fraction of acetic acid molecules donate a proton (H⁺) to water molecules, forming hydronium ions (H₃O⁺) and acetate ions (CH₃COO⁻). The presence of these ions allows the solution to be weakly conducting, as they are free to move and carry an electric charge. Additionally, since there is an excess of H₃O⁺ ions, the solution is acidic in nature, causing a decrease in pH.

3. Comparing the Dissolution Processes and Their Results

In summary, the main difference between the dissolution of methanol and acetic acid lies in the presence of ions in the solution. While both compounds form hydrogen bonds with water, methanol does not release any ions and its solution remains nonconducting. On the other hand, acetic acid undergoes partial ionization and forms a weakly conducting, acidic solution due to the presence of hydronium and acetate ions. Therefore, the observed differences in conductivity and acidity between the two solutions can be attributed to the difference in their ionization properties when dissolved in water.