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Question

An organic liquid ‘A’ containing C, H and O with pKa value 15.9, used in polishing woods, on heating with concentrated sulphuric acid gives a gaseous product ‘B’ with the empirical formula, \(\mathrm{CH_2}\). ‘B’ decolourises bromine water as well as dilute permanganate solution. The compound A and B are respectively

The correct answer is

ethanol and ethene

A liquid of C, H, O with \(\mathrm{p}K_a\approx 15.9\) used in wood polishes (as a solvent for shellac/varnish) is ethanol.

On heating with concentrated \(\mathrm{H_2SO_4}\) (443 K), ethanol is dehydrated: \(\mathrm{C_2H_5OH\rightarrow CH_2=CH_2+H_2O}\)

Ethene, \(\mathrm{C_2H_4}\), has empirical formula \(\mathrm{CH_2}\) and, being unsaturated, decolourises bromine water and dilute (Baeyer’s) permanganate.

Hence, ethanol and ethene.

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Important Questions from Organic Chemistry

  1. In Dumas method for estimation of nitrogen, 0.50 g of an organic compound gave 70 mL of nitrogen collected at 300 K and 715 mm pressure. The percentage of nitrogen in the organic compound is ______ %.
    (Aqueous tension at 300 K is 15 mm).
  2. $0.25 \text{ g}$ of an organic compound "A" containing carbon, hydrogen and oxygen was analysed using the combustion method. There was an increase in mass of $\text{CaCl}_2$ tube and potash tube at the end of the experiment. The amount was found to be $0.15 \text{ g}$ and $0.1837 \text{ g}$, respectively. The percentage of oxygen in compound A is ______ %. (Nearest integer)
    (Given: molar mass in $\text{g mol}^{-1}$ $\text{H} : 1, \text{C} : 12, \text{O} : 16$)
  3. Grignard reagent $\text{RMgBr (P)}$ reacts with water and forms a gas $\text{(Q)}$. One gram of Q occupies $1.4 \text{ dm}^3$ at STP. (P) on reaction with dry ice in dry ether followed by $\text{H}_3\text{O}^+$ forms a compound $\text{(Z)}$. 0.1 mole of $\text{(Z)}$ will weigh _________ g. (Nearest integer)
  4. Consider all the structural isomers with molecular formula $\text{C}_5\text{H}_{11}\text{Br}$ are separately treated with $\text{KOH(aq)}$ to give respective substitution products, without any rearrangement. The number of products which can exhibit optical isomerism from these is ___________.
  5. The major products U and V in the following reaction are

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