which of the following is a weak acid: hydrochloric acid, nitric acid, ethanoic acid, or sulfuric acid?
Which of the following is a weak acid: hydrochloric acid, nitric acid, ethanoic acid, or sulfuric acid?
Answer: Among the acids listed, ethanoic acid (also known as acetic acid, with the chemical formula CH₃COOH) is classified as a weak acid. Let’s explore why ethanoic acid is a weak acid and compare it with the others mentioned:
What is a Weak Acid?
Weak acids only partially dissociate in solution, meaning they only ionize a small fraction of their molecules in water. This results in a relatively low concentration of hydrogen ions (H^+), leading to a higher pH compared to strong acids of the same concentration.
Comparison of the Acids:
-
Hydrochloric Acid (HCl):
- Dissociation: HCl \rightarrow H^+ + Cl^-
- Nature: Strong Acid
- Explanation: Hydrochloric acid completely dissociates into hydrogen ions and chloride ions in aqueous solution, making it a strong acid.
-
Nitric Acid (HNO₃):
- Dissociation: HNO_3 \rightarrow H^+ + NO_3^-
- Nature: Strong Acid
- Explanation: Nitric acid is strong as it fully dissociates in water, releasing hydrogen ions entirely.
-
Ethanoic Acid (CH₃COOH):
- Dissociation: CH_3COOH \leftrightarrow CH_3COO^- + H^+
- Nature: Weak Acid
- Explanation: Only partially dissociates in solution, resulting in an equilibrium between the acid and its ions.
-
Sulfuric Acid (H₂SO₄):
- Dissociation: In the first step, it dissociates completely: H_2SO_4 \rightarrow H^+ + HSO_4^-. In the second step, HSO_4^- \leftrightarrow H^+ + SO_4^{2-}.
- Nature: Strong Acid
- Explanation: The first dissociation of sulfuric acid is complete, contributing to its strong acidic nature.
Factors Contributing to Acid Strength:
- Degree of Ionization: Strong acids ionize completely, while weak acids like ethanoic acid only partially ionize in solution.
- Acid Dissociation Constant (Ka): Weak acids have a lower K_a value compared to strong acids, indicating less dissociation.
- pH Level: Weak acids have higher pH values than strong acids when at the same molar concentration.
Ethanoic Acid in Focus:
- Acid Dissociation Constant (Ka): The K_a of ethanoic acid is approximately 1.8 \times 10^{-5}, signifying its partial ionization.
- pH Example: For a 1 M solution of ethanoic acid, the pH is around 2.4, significantly higher than that of strong acids at the same concentration.
- Everyday Use: Found in vinegar, ethanoic acid is widely used in food preservation and cooking. Its weaker nature is why it is safe for culinary use compared to strong acids, which are highly corrosive.
Conclusion:
Among the given options, ethanoic acid is the only weak acid due to its incomplete dissociation in water. Understanding these differences is fundamental for various applications in chemistry and industry. If you have further inquiries or need more detailed explanations on any of these acids, feel free to ask!