A carbon compound P on heating with excess concentrated sulphuric acid forms another carbon compound Q which on addition of hydrogen in the presence of nickel catalyst
forms a saturated carbon compound R one molecule of Roman on combustion forms two molecules of CO2 and 3 molecules of H2O find P Q R and write their chemical equation
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The compounds P, Q, and R are ethanol, ethene, and ethane respectively.
C₂H₅OH (P) + conc.H₂SO₄ → C₂H₄ (Q) + H₂O
C₂H₂ (Q) + 2H₂ + Ni → C₂H₆ (R)
C₂H₆ (R) + (7/2) O₂ + ∆ → 2CO₂ + 3H₂O
• To solve questions like these, we should start collecting hints from backwards, instead of proceeding in the forward direction.
• The last clue in the question says that the compound 'R' on combustion gives 2 molecules of CO₂ and 3 molecules of H₂O.
Number of C atoms in 2CO₂ = 2
Number of H atoms in 3H₂O = 3 × 2 = 6
• We know that a hydrocarbon on combustion gives CO₂ and H₂O. This implies that the compound 'R' is a hydrocarbon containing 2 atoms of carbon and 6 atoms of hydrogen. Therefore, the compound 'R' is inferred to be C₂H₆ (ethane).
• The chemical equation for the above reaction can be represented as :
C₂H₆ (R) + (7/2) O₂ + ∆ → 2CO₂ + 3H₂O
• The next clue says that the hydrogenation of compound 'Q' in the presence of nickel catalyst produces compound 'R'.
• We have derived that the compound 'R' is an alkane. Hydrogenation of an alkene produces the corresponding alkane. This implies that compound 'R', ethane is produced by the hydrogenation of ethene. Therefore, the compound 'Q' is concluded to be ethene.
• The chemical equation for the above reaction is given as :
C₂H₂ (Q) + 2H₂ + Ni → C₂H₆ (R)
• It has also been said that the compound 'Q' is produced by the reaction of compound 'P' with conc. H₂SO₄.
• Compound 'Q' is an alkene. Dehydration of an alcohol with conc. H₂SO₄ produces an alkene with the same number of carbon atoms. This implies that compound 'P' is an alcohol.
• Since 'Q' is ethene, it must be produced by the dehydration of ethanol. Therefore, compound 'P' is ethanol.
• The chemical equation for the above reaction is :
C₂H₅OH (P) + conc.H₂SO₄ → C₂H₄ (Q) + H₂O