Give a chemical test to distinguish between a ethanal and propanal ?

Answer

To distinguish between ethanal (acetaldehyde) and propanal (propionaldehyde), we can use the Iodoform test. Here’s a step-by-step solution:

### Step 1: Identify the Structures
- **Ethanal (Acetaldehyde)**: The structure is CH₃CHO.
- **Propanal (Propionaldehyde)**: The structure is CH₃CH₂CHO.

### Step 2: Understand the Iodoform Test
The Iodoform test is a chemical test that detects the presence of a methyl ketone or an aldehyde with a methyl group adjacent to the carbonyl group (ketomethyl group). The reagent used for this test is iodine (I₂) in the presence of sodium hydroxide (NaOH) or sodium hypoiodite (NaOI).

### Step 3: Perform the Test on Ethanal
1. **Reaction with Iodoform Reagent**:
- When ethanal (CH₃CHO) is treated with the Iodoform reagent (I₂/NaOH), it contains a methyl group adjacent to the carbonyl group.
- This allows ethanal to undergo the Iodoform reaction, producing a yellow precipitate of iodoform (CHI₃).

**Reaction**:
\[ CH₃CHO + 3 I₂ + 4 NaOH \rightarrow CHI₃ + HCOONa + 3 NaI + 3 H₂O \]

2. **Observation**: A yellow precipitate (CHI₃) is formed.

### Step 4: Perform the Test on Propanal
1. **Reaction with Iodoform Reagent**:
- When propanal (CH₃CH₂CHO) is treated with the Iodoform reagent, it does not contain a methyl group adjacent to the carbonyl group.
- Therefore, propanal does not undergo the Iodoform reaction.

**Observation**: No yellow precipitate is formed.

### Conclusion
- **Result**: The formation of a yellow precipitate indicates the presence of ethanal, while the absence of a precipitate indicates propanal.
- Thus, the Iodoform test can effectively distinguish between ethanal and propanal.