Keerthi thinks that Substitution reaction occurs in saturated Hydrocarbons, on the contrary Krishi thinks

Question

(i) “Keerthi thinks that Substitution reaction occurs in saturated Hydrocarbons, on the contrary Krishi thinks, it occurs in unsaturated Hydrocarbons.” Justify with valid reasoning whose thinking is correct.

(ii) “Methane and Propane and their Isomers are used as fuels” Comment. Draw the electron dot structure of the immediate lower homologue of Propane. Give any two characteristics of homologues of a given homologous series.

(iii) A mixture of oxygen and ethyne is burnt for welding. Can you predict why a mixture of ethyne and air is not used?

Answer 1

(i) Keerthi’s thinking is correct as substitution reactions occur in saturated hydrocarbons, hydrogen atoms are replaced with heteroatoms in saturated hydrocarbons. Whereas in unsaturated hydrocarbons an addition reaction occurs, simple molecules are added across double and/or triple bonds. 

(ii) Methane and propane undergo combustion reaction in presence of oxygen and produce large amount of energy. 

The lower homologue of propane is ethane has the following electron dot structure: 

Any two characteristics -

• Difference in -CH2- / 14u molecular mass of any two adjacent homologues. 
• Same general formula/ functional group - 
• Similar chemical properties - 
• Gradual change in physical properties 

(iii) The mixture of ethyne and oxygen in sufficient amounts undergoes complete combustion to fire a clean blue flame. In pressure of insufficient supply of oxygen or in the presence of air, ethyne does not undergo complete combustion and produces sooty flame.