Q3. How would you tell ethanol from methanol in the laboratory?
By the iodoform test: ethanol has a CH3–CH(OH)– group and gives yellow iodoform; methanol does not (Lab Manual, page 88).
Q4. Give two tests that tell phenol from ethanol.
Neutral ferric chloride: phenol gives a violet colour, ethanol none (Lab Manual, page 90). Phthalein dye test: phenol heated with phthalic anhydride and concentrated H2SO4, then poured into dilute NaOH, gives pink phenolphthalein; ethanol gives no colour (Lab Manual, pages 90–91; reasoned for ethanol). Ethanol, for its part, gives yellow iodoform and phenol does not (reasoned from NCERT Unit 8, page 240). Solubility in NaOH does not tell them apart: lower alcohols such as ethanol mix with water in all proportions (NCERT page 204), so ethanol dissolves in aqueous NaOH too.
Q5. Why does 2,4,6-trinitrophenol dissolve in sodium hydrogencarbonate solution when phenol does not?
Its three nitro groups withdraw electrons and stabilise the phenoxide ion, making it a strong enough acid to react with hydrogencarbonate (Lab Manual, page 91; NCERT page 207).
Q6. Which test, Lucas or iodoform, tells propan-2-ol from propan-1-ol, and what do you see?
Either works. Lucas: propan-2-ol (2°) separates a layer within 1–5 minutes; propan-1-ol (1°) does not. Iodoform: propan-2-ol, CH3CH(OH)CH3, gives yellow iodoform; propan-1-ol does not (reasoned from Lab Manual, page 88).
Q7. The Lab Manual’s potassium iodide–iodine reagent has 20 g of KI and 10 g of I2 in 100 mL of water. How many moles of each are in 100 mL? (K = 39.1, I = 126.9.)
KI: 20/166.0 = 0.12 mol; I2: 10/253.8 = 0.039 mol, about three moles of KI for each mole of I2 (reasoned from Lab Manual, page 89).