Q3. What volume of carbon dioxide, at 273.15 K and 1 bar, is released when 90 g of glucose is fully fermented, and what mass of ethanol forms? (C = 12, H = 1, O = 16; molar volume 22.7 L mol−1.)
C6H12O6 → 2C2H5OH + 2CO2. 90/180 = 0.50 mol of glucose gives 1.0 mol of CO2, 1.0 × 22.7 = 22.7 L, and 1.0 mol of ethanol, 46 g (reasoned from NCERT page 214).
Q4. A fermenting fruit juice still contains sugar when its alcohol content reaches about 14 percent. What happens next, and why?
Fermentation stops: the action of zymase is inhibited once the alcohol formed exceeds 14 percent, so the remaining sugar is not fermented (NCERT page 214).
Q5. Why does wine turn sour if air gets into the fermentation vessel?
The oxygen of air oxidises ethanol to ethanoic acid, which destroys the taste (NCERT page 214).
Q6. Using Le Chatelier’s principle, explain why methanol is made from CO and H2 at high pressure.
CO(g) + 2H2(g) ⇌ CH3OH(g): 3 mol of gas give 1 mol (Δng = −2), so a high pressure shifts the equilibrium towards methanol (reasoned from NCERT Class 11 Chemistry, Unit 6, and NCERT page 214).
Q7. Ethanol boils at 351 K and methanol at 337 K. Give a reason for the difference.
Both are hydrogen bonded, but ethanol has one more carbon: boiling points of alcohols rise with the number of carbon atoms, as van der Waals forces grow (NCERT pages 203 and 214).