This video lecture from Aliphatic Hydrocarbons (F.Sc. second year Chemistry) covers the preparation of Alkenes (Part 1). The first method which is discussed includes the dehydrohalogenation (removal of halogen group and a hydrogen atom from adjacent carbon) of an alkyl halide by a base like KOH in the presence of alcohol (methyl or ethyl). A pi bond is formed between the two carbon atoms with unpaired electron yielding an alkene. The second method is the removal of hydroxyl group and a hydrogen from adjacent carbon (hence dehydration) or removal of water from an alcohol (hydrocarbons with –OH). Dehydrating agents like sulphuric acid are used in different concentrations and temperatures with primary, secondary and tertiary alcohols yielding alkenes. Find more e-learning material and educational video lectures in Urdu at maktab.pk. These videos are free to use for promotional and commercial purpose by keeping the credits to Maktab.