IUPAC, isomerism, mechanisms MCQs

Q1. Bromine in CCl4 (orange-red colour) is decolourised by which of the following Class-10 compounds in the cold and dark?

• A.But-2-ene
• B.Butane
• C.Methanol
• D.Cyclopentane

Answer: A. But-2-ene

Q2. Ethanol can be distinguished from ethanoic acid by which of the following SINGLE chemical tests?

• A.Sodium bicarbonate (NaHCO3) - only ethanoic acid liberates CO2 brisk effervescence.
• B.Sodium metal - both liberate H2.
• C.Phenolphthalein - neither is coloured.
• D.Litmus paper - both turn blue litmus red.

Answer: A. Sodium bicarbonate (NaHCO3) - only ethanoic acid liberates CO2 brisk effervescence.

What's the underlying rule? NaHCO3 + RCOOH → RCOONa + H2O + CO2↑, but NaHCO3 does NOT react with ethanol (alcohols are too weakly acidic). Hence brisk effervescence cleanly identifies the acid. Na metal reacts with BOTH alcohols and acids to give H2, so it cannot distinguish. Ethanol does NOT turn blue litmus red. Pick: A) Sodium bicarbonate (NaHCO3) - only ethanoic acid liberates CO2 brisk effervescence.

Q3. How many moles of H2 will saturate 1 mole of 1,3-butadiene (CH2=CH-CH=CH2)?

• A.2
• B.1
• C.3
• D.4

Answer: A. 2

Given 2, 1, 1, 3, 2, asked for How many moles of H2 will saturate 1 mole of 1,3-butadiene (CH2=CH-CH=CH2)?. By Two C=C π-bonds → 2 mol H2 needed to give butane. Two C=C π-bonds → 2 mol H2 needed to give butane. Putting it together option A) 2.