Q3. Which of these give iodoform when warmed with iodine and alkali: ethanol, methanol, propanal, butan-2-one, pentan-3-one, acetophenone?
Ethanol (its CH3CH(OH)– group oxidises to CH3CO–), butan-2-one, CH3COCH2CH3, and acetophenone, C6H5COCH3. Methanol, propanal, CH3CH2CHO, and pentan-3-one, CH3CH2COCH2CH3, have no CH3CO– or CH3CH(OH)– group and do not (reasoned from NCERT page 240).
Q4. Write the overall equation for iodoform from ethanal with iodine and sodium hydroxide.
CH3CHO + 3I2 + 4NaOH → CHI3 + HCOONa + 3NaI + 3H2O: the CH3CO– group of ethanal leaves sodium methanoate, an acid salt with one carbon atom fewer (reasoned from NCERT page 240).
Q5. How many moles and grams of NaOH does 0.58 g of acetone need by the equation for iodoform from acetone? (C = 12, H = 1, O = 16, Na = 23.)
0.58/58 = 0.010 mol of acetone needs 4 × 0.010 = 0.040 mol of NaOH, M = 40 g mol−1: 0.040 × 40 = 1.6 g (reasoned).
Q6. Your dried crystals melt at about 112 °C. What does this suggest, and what would you do?
Pure iodoform melts at 119 °C (Remsen, page 28; Wikipedia, “Iodoform”), so a depressed or broad range suggests impurities or retained solvent, but thermometer calibration and heating rate also matter. Check the apparatus and record the full range; if needed, purify using the instructor’s approved recrystallisation procedure and remeasure.