WAEC Chemistry 2019 Paper

Concept:Ethane is an alkane, so chlorine reacts with it by substitution, not addition.Explanation:When ethane ($\mathrm{C_2H_6}$) is mixed with chlorine, chlorine atoms replace the hydrogen atoms.With excess chlorine, two hydrogen atoms are replaced by two chlorine atoms.The reaction is:$\mathrm{C_2H_6 + 2Cl_2 \xrightarrow{UV} ClCH_2CH_2Cl + 2HCl}$The chlorine atoms attach to different carbon atoms in the ethane chain.This gives the compound $\mathrm{ClCH_2CH_2Cl}$, which is named 1,2-dichloroethane.It is also commonly known as ethylene dichloride.The unsaturated options would require a double bond, which ethane does not contain.Answer:A. 1,2-dichloroethane