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)

Explanation

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

### Step 1: Understand the Nature of Orthoboric Acid
Orthoboric acid (H₃BO₃) is a weak acid. It does not dissociate completely in water like strong acids do. Instead, it behaves more like a Lewis acid, forming a complex with hydroxyl ions.

**Hint:** Remember that weak acids do not fully dissociate in solution, which affects how we can titrate them.

### Step 2: Identify the Role of Sodium Hydroxide
Sodium hydroxide (NaOH) is a strong base. When titrating a weak acid with a strong base, the equivalence point will occur when the amount of base added is stoichiometrically equivalent to the amount of acid present.

**Hint:** Strong bases can neutralize weak acids, but the presence of certain compounds can change the dynamics of the titration.

### Step 3: Recognize the Importance of Indicators
Phenolphthalein is a pH indicator that changes color at a pH of around 8.2 to 10. In the titration of a weak acid with a strong base, the endpoint will occur at a higher pH than with strong acid-strong base titrations.

**Hint:** The choice of indicator is crucial; it must change color at the pH where the reaction reaches equivalence.

### Step 4: Understand the Need for Polyhydroxyl Compounds
For the titration of orthoboric acid with sodium hydroxide using phenolphthalein, the presence of polyhydroxyl compounds (like cis-glycerol and catechol) is necessary. These compounds help to stabilize the formation of a cyclic complex with boric acid, thus increasing the effective concentration of hydronium ions (H⁺) in the solution.

**Hint:** Polyhydroxyl compounds enhance the acidity of the solution, allowing for a clearer endpoint when using phenolphthalein.

### Step 5: Conclude the Answer
Therefore, the aqueous solution of orthoboric acid can be titrated against sodium hydroxide using phenolphthalein indicator only in the presence of polyhydroxyl compounds such as cis-glycerol and catechol. The correct answer to the question is that both catechol and cis-glycerol are required.

**Final Answer:** The titration can be performed in the presence of catechol and cis-glycerol (Option D).