Explain why HCl is a strong acid and CH3COOH is a weak acid. How can it be verified?
The Correct Answer and Explanation is:
Answer:
HCl is a strong acid because it completely ionizes in water, releasing all of its hydrogen ions (H⁺). CH₃COOH (acetic acid) is a weak acid because it only partially ionizes in water, with most of the acid molecules remaining intact.
Explanation:
Hydrochloric acid (HCl) is classified as a strong acid due to its complete dissociation in aqueous solution. When HCl is added to water, it ionizes fully, producing hydrogen ions (H⁺) and chloride ions (Cl⁻). No undissociated HCl molecules remain in solution. The reaction can be represented as:
HCl → H⁺ + Cl⁻
This complete ionization results in a high concentration of hydrogen ions, leading to a low pH and strong acidic behavior.
In contrast, acetic acid (CH₃COOH), the main component of vinegar, is a weak acid. It only partially dissociates in water. The majority of acetic acid molecules remain undissociated, and only a small fraction releases hydrogen ions. Its dissociation is represented as an equilibrium:
CH₃COOH ⇌ H⁺ + CH₃COO⁻
The double arrow indicates that the reaction does not go to completion. This partial ionization results in a lower concentration of free hydrogen ions, higher pH values compared to strong acids, and milder acidic behavior.
This difference in ionization strength can be verified through several experimental methods:
- Electrical Conductivity: Strong acids like HCl produce more ions and therefore conduct electricity better than weak acids like CH₃COOH.
- pH Measurement: At the same concentration, HCl shows a lower pH due to more H⁺ ions in solution.
- Reaction with Metals or Carbonates: HCl reacts vigorously with metals such as zinc, producing more hydrogen gas compared to CH₃COOH of the same concentration.
- Titration Curve: The pH curve of HCl during neutralization with a base has a sharp change at the equivalence point, while CH₃COOH shows a more gradual change.
These observations confirm the stronger acidity of HCl and the weaker nature of CH₃COOH.
