Question

Number of replaceable hydroxyl groups in one molecule of a base is ------

• A. Basicity
• B. Acidity
• C. Reduction
• D. Oxidation

Hint:

To avoid confusion:
- Bases have "Acidity" (number of replaceable \(\text{OH}^-\) groups).
- Acids have "Basicity" (number of replaceable \(\text{H}^+\) groups).
The terms are defined inversely.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The concentration of acids and bases can be described in terms of their equivalent weights, which depend on the number of replaceable hydrogen (\(\text{H}^+\)) or hydroxyl (\(\text{OH}^-\)) ions they contain.

Step 2: Detailed Explanation:
According to classical acid-base definitions:
- The number of replaceable hydroxyl (\(\text{OH}^-\)) groups in one molecule of a base is defined as its acidity.
For example:
- Sodium hydroxide (\(\text{NaOH}\)) has one replaceable \(\text{OH}^-\) group, so its acidity is 1 (monoacidic base).
- Calcium hydroxide (\(\text{Ca(OH)}_2\)) has two replaceable \(\text{OH}^-\) groups, so its acidity is 2 (diacidic base).
- Aluminum hydroxide (\(\text{Al(OH)}_3\)) has three replaceable \(\text{OH}^-\) groups, so its acidity is 3 (triacidic base).
Conversely:
- The number of replaceable hydrogen (\(\text{H}^+\)) ions in one molecule of an acid is defined as its basicity.
For example, \(\text{HCl}\) is monobasic (basicity = 1), while \(\text{H}_2\text{SO}_4\) is dibasic (basicity = 2).
This terminology reflects the amount of acid required to neutralize a base (acidity) or the amount of base required to neutralize an acid (basicity).

Step 3: Final Answer:
The number of replaceable hydroxyl groups in a base is known as Acidity.