One mL of an organic compound was dissolved in ethanol and a very small drop of dilute alkali was added to it and them a drop of phenolphalein was added. The red colour of the indicator was seen . The mixture. was then heated . The colour disappeared in a few minutes . The organic compound is most likely to be

Options

A. an aldehyde
B. a ketone
C. a carboxylic acid
D. an ester

Answer

To solve the question, we need to analyze the steps and the reactions that occur when the organic compound is treated with ethanol, dilute alkali, and phenolphthalein. Here’s a step-by-step breakdown:

### Step 1: Understanding the Initial Setup
1. **Dissolving the Organic Compound**: We start with 1 mL of an organic compound dissolved in ethanol. Ethanol is a common solvent for organic reactions.

**Hint**: Consider the properties of ethanol and how it interacts with different types of organic compounds.

### Step 2: Adding Dilute Alkali
2. **Adding Dilute Alkali**: A very small drop of dilute alkali (like NaOH) is added. This indicates that the organic compound may have acidic properties or can react with the alkali.

**Hint**: Think about how different organic compounds (like acids, esters, etc.) would react with an alkali.

### Step 3: Adding Phenolphthalein
3. **Adding Phenolphthalein**: After adding the alkali, a drop of phenolphthalein is added, which turns red. This indicates that the solution is basic (pH > 8.2).

**Hint**: Recall that phenolphthalein is an acid-base indicator that changes color based on the pH of the solution.

### Step 4: Heating the Mixture
4. **Heating the Mixture**: The mixture is then heated, and the red color disappears after a few minutes. This disappearance of color suggests that the alkali is being consumed in a reaction.

**Hint**: Consider what reactions could occur upon heating that would consume the alkali and lead to a change in pH.

### Step 5: Identifying the Organic Compound
5. **Analyzing the Reaction**: The disappearance of red color indicates that the alkali (NaOH) is reacting with the organic compound. If the organic compound were a carboxylic acid, the alkali would neutralize it, but phenolphthalein would not show red initially with a carboxylic acid. Thus, it cannot be a carboxylic acid.

**Hint**: Think about the hydrolysis of esters in the presence of a base and how this would affect the pH.

### Conclusion
6. **Final Identification**: The organic compound is most likely an ester. When heated with dilute alkali, the ester undergoes hydrolysis to form a sodium salt of the corresponding carboxylic acid and alcohol, consuming the alkali and causing the red color to disappear.

**Final Answer**: The organic compound is most likely an ester.