A carbon compound ‘P’ on heating with excess conc. H 2 SO 4 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 ‘R’ on combustion forms two molecules of carbon dioxide and three molecules of water. Identify P, Q and R and write chemical equations for the reactions involved.



  • On combustion, compound R forms carbon dioxide and water. So, R is an alkane. Since 2 molecules of carbon dioxide are formed, R is an alkane with 2 carbon atoms. 

Therefore, R is Ethane.

  • When hydrogen is added to compound Q in the presence of a nickel catalyst, ethane is formed. Ethane is a saturated hydrocarbon. Hydrogenation of unsaturated carbon compounds gives saturated hydrocarbons. Therefore, Q is an unsaturated carbon compound with 2 carbon atoms. 

So, Q is Ethene.

  • When alcohols are heated in the presence of conc H 2 SO 4 , dehydration reaction takes place and alkenes are formed. When compound P is heated in the presence of conc H 2 SO 4 , Ethene is formed. So, P is an alcohol with 2 carbon atoms.

Therefore, P is Ethanol.


  • Compound P is Ethanol
  • Compound Q is Ethene
  • Compound R is Ethane

The reactions that take place are:

Reaction of Ethanol with conc H2SO4 - Teachoo.png

Reaction of Ethene with Hydrogen:

Reaction of Ethene with Hydrogen - Teachoo.png


Reaction of Ethanol with conc H2SO4 Ethanol Concd H2SO4 180℃ Excess acid Ethylene HOH

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CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo