Question: Which one of the following is a weak acid?
- A. Acetic acid
- B. Formic acid
- C. Carbonic acid
- D. All of the above
Correct Answer: D. All of the above
Explanation
A weak acid is an acid that partially dissociates into ions when dissolved in water. This means that only a part of the acid molecules releases hydrogen ions (H⁺), while the remaining molecules stay undissociated.
Let us understand the given options one by one.
1. Acetic Acid (CH₃COOH): Acetic acid is a weak acid commonly found in vinegar. It partially dissociates into hydrogen ions and acetate ions in water.
2. Formic Acid (HCOOH): Formic acid is also a weak acid. It partially ionises in water and is naturally found in the venom of some ants.
3. Carbonic Acid (H₂CO₃): Carbonic acid is a weak acid formed when carbon dioxide dissolves in water. It partially dissociates into hydrogen ions and bicarbonate ions.
All three acids undergo partial ionisation in water. Therefore, acetic acid, formic acid, and carbonic acid are classified as weak acids.
Hence, Option D (All of the above) is the correct answer.
Important Note: Understanding the pH Scale
The pH scale is used to measure how acidic or basic a solution is. It generally ranges from 0 to 14 at 25°C.
- pH below 7: Acidic solution
- pH equal to 7: Neutral solution
- pH above 7: Basic or alkaline solution
Remember that acid strength and pH are not the same thing. Acid strength depends on how readily an acid ionises in water, while pH also depends on the concentration of the acid.
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