Aqueous solution of orthoboric acid can be titrated against sodium hydroxide using phenolphthalein indicator only in presence of

Options

A. trans - glycerol
B. catechol
C. cis-glycerol
D. both (B) and (C)

Answer

To solve the question regarding the titration of orthoboric acid with sodium hydroxide using phenolphthalein as an indicator, we can break down the solution into the following steps:

### Step 1: Understand the Components
- **Orthoboric Acid (H3BO3)**: A weak acid that can react with strong bases.
- **Sodium Hydroxide (NaOH)**: A strong base that will react with the weak acid.
- **Phenolphthalein**: A pH indicator that changes color depending on the acidity or basicity of the solution.

**Hint**: Identify the nature of the acid and base involved in the reaction.

### Step 2: Reaction Between Orthoboric Acid and Sodium Hydroxide
When orthoboric acid reacts with sodium hydroxide, it forms a complex:
\[ \text{H}_3\text{BO}_3 + \text{NaOH} \rightarrow \text{NaBOH}_4 + \text{H}_2\text{O} \]
However, this complex (NaBOH4) is unstable and can hydrolyze back to its components.

**Hint**: Consider the stability of the products formed in the reaction.

### Step 3: Role of Phenolphthalein
Phenolphthalein is colorless in acidic solutions and turns pink in basic solutions. For the titration to be successful, the endpoint must be detectable, which requires a stable complex to form.

**Hint**: Recall how phenolphthalein behaves in different pH environments.

### Step 4: Need for Stabilizing Agents
To stabilize the complex formed during the titration, we need to add certain compounds. Specifically, cis-diols like catechol and cis-glycerol can stabilize the borate complex, preventing it from hydrolyzing back into the weak acid and strong base.

**Hint**: Identify which compounds can stabilize the reaction products.

### Step 5: Conclusion
The question asks under what conditions orthoboric acid can be titrated with sodium hydroxide using phenolphthalein. The presence of cis-diols (like catechol and cis-glycerol) is necessary to stabilize the complex and allow for a clear endpoint detection.

Thus, the correct answer is that the titration can occur in the presence of both catechol and cis-glycerol.

**Final Answer**: Both B (Catechol) and C (Cis-glycerol).