Question

Methanol, \(\mathrm{CH}_{3} \mathrm{OH}\), and hydrogen chloride, \(\mathrm{HCl}\), are both molecular substances, yet an aqueous solution of methanol does not conduct an electrical current, whereas a solution of \(\mathrm{HCl}\) does conduct. Account for this difference. [Section 4.1]

Short answer

The primary difference between methanol (CH₃OH) and hydrogen chloride (HCl) in aqueous solutions is the formation of ions. Methanol dissolves in water as neutral molecules due to hydrogen bonding, while HCl dissociates into hydronium (H₃O⁺) and chloride (Cl⁻) ions. Since the HCl solution contains mobile ions, it conducts electricity, whereas the methanol solution doesn't contain mobile ions and does not conduct electricity.

Step-by-step solution

Investigate the structures of CH₃OH and HCl

Both methanol (CH₃OH) and hydrogen chloride (HCl) are molecular compounds. Methanol is an alcohol, which contains an -OH group, while HCl is a diatomic molecule consisting of a hydrogen atom bonded to a chlorine atom.

Understand solubility in water

When a substance is added to water, it may dissolve to produce a homogeneous solution due to the interactions between the solute and the solvent (water) molecules. In the case of methanol, it is a polar molecule that can form hydrogen bonds with water molecules, thus allowing it to dissolve. However, the solubility of HCl in water is associated with a more extensive ionization process. When HCl gas is dissolved in water, it reacts with the water molecules to form hydronium ions (H₃O⁺) and chloride ions (Cl⁻): \[HCl(g) + H_2O(l) \rightarrow H_3O^+(aq) + Cl^-(aq)\]

Analyze the electrical conductivity of the solutions

A substance conducts electricity when it contains mobile charge carriers, such as ions, that can move freely. In an aqueous solution of methanol, CH₃OH remains as a neutral molecule and does not produce any ions, rendering the solution non-conductive. On the other hand, as seen in step 2, HCl dissociates in water to produce hydronium ions (H₃O⁺) and chloride ions (Cl⁻). These ions can move freely, allowing the solution to conduct an electrical current.

Conclusion

The primary difference between methanol (CH₃OH) and hydrogen chloride (HCl) in aqueous solutions is the formation of ions. Methanol dissolves in water as neutral molecules due to hydrogen bonding, while HCl dissociates into hydronium (H₃O⁺) and chloride (Cl⁻) ions. Since the HCl solution contains mobile ions, it conducts electricity, whereas the methanol solution doesn't contain mobile ions and does not conduct electricity.