(a) Differentiate between alkanes and alkenes. Name and draw the structure of one member of each. [CBSE 2013] (b) Alkanes generally burn with clean flame. Why?
Alkanes: An alkane is a hydrocarbon in which the carbon atoms are connected by only single covalent bond. General formula of alkane is CnH2n+2. The simplest alkane is methane (CH4). Alkanes generally burn in air with a blue and non-sooty flame. Alkanes undergo substitution reactions. Alkanes do not decolourise red brown colour of bromine water. alkenes: An alkene is an unsaturated hydrocarbon in which the two carbon atoms are connected by a double bond. General formula of alkene is CnH2n. The simplest alkene is ethene (C2H4). Alkenes burn in air with a yellow and sooty flame. Alkenes undergo addition reactions. Alkenes decolourise bromine water. (b) Alkanes burn in air with a blue and non-sooty flame because the percentage of carbon in the alkane is comparatively low which gets oxidised completely by oxygen present in air.
