Question

Write a simple chemical test to distinguish between Ethanal and Propanal.

Hint:

Compounds containing the \(CH_3CO-\) group generally give a positive iodoform test.

Answer 1

Concept: Ethanal contains the structural unit \[ CH_3CO- \] and therefore behaves similarly to methyl ketones in the iodoform test. Propanal does not contain this structural feature and hence does not respond to the iodoform test. Thus, the iodoform test can be used to distinguish between the two compounds.

Step 1: Perform iodoform test Treat both compounds with iodine and aqueous sodium hydroxide. \[ I_2/NaOH \]

Step 2: Observation for ethanal Ethanal gives a yellow precipitate of iodoform. \[ CHI_3 \] \[ \boxed{\text{Yellow precipitate formed}} \]

Step 3: Observation for propanal Propanal does not produce any yellow precipitate. \[ \boxed{\text{No yellow precipitate}} \]

Final Answer \[ \boxed{\text{Iodoform test}} \] Ethanal gives yellow precipitate of iodoform whereas propanal does not.