Which of the following compounds would give addition reactions ?
(i) C2H6
(ii) C3H8
(iii) C2H4
(iv) C4H10
(v) C5H8
Sol:
Only unsaturated compounds like alkenes and alkynes (which contain double bonds or triple bonds) give addition reactions.
So, all that we have to do in this problem is to find out alkenes and alkynes from the list of above given hydrocarbons.
If we look carefully at the above compounds, we will find that only C2H4 and C5H8 are unsaturated hydrocarbons.
(i) C2H4 is an alkene which corresponds to the general formula CnH2n (having n = 2).
(ii) C5H8 is an alkyne which corresponds to the general formula CnH2n – 2 (having n = 5).
Thus only C2H4 and C5H8 would give addition reactions.
Please note that all the remaining compounds like C2H6, C3H8 and C4H10 are alkanes which correspond to the general formula CnH2n+ 2 (having n = 2,
3 and 4 respectively).
Alkanes are saturated compounds which do not give addition reactions.
Q2
You are provided with three jars containing methane, ethene and ethyne respectively. What tests will you carry out to distinguish between them?
Sol:
Methane, ethene and ethyne can be identified by using bromine - water and ammoniacal cuprous chloride solution.
(i)Methane does not decolorize bromine water. Ethene and ethyne decolorize the red - brown color of bromine water.
Thus, methane can be distinguished from ethene and ethyne by the bromine water test.
(ii)Ethene does not react with ammoniacal cuprous chloride solution but ethyne gives a red brown precipitate with ammoniacal cuprous chloride solution.
Thus, ethyne can be distinguished from ethene by the cuprous chloride test.