A gaseous mixture containing two neighbour hydrocarbons of the same homologous series was 14.4 times as dense as hydrogen. This mixture with a volume of 16.8 dm3 was hydrated and 350 g of the solution were obtained when the products of hydration were absorbed in water. Ten grams of this solution were taken and heated in the presence of silver(I) oxide which was prepared from 70 cm3 of a 1 N silver(I) nitrate solution. Unreacted Ag2O was dissolved in an aqueous ammonia solution and a residual precipitate was filtered off. The filtrate was acidified with nitric acid and addition of an excess of sodium bromide to it resulted in 9.4 g of a precipitate. When the mixture of the hydrocarbons that remained unreacted, was mixed with a 50 % excess of hydrogen and transmitted above a heated Pt-catalyst, its resulting volume decreased to 11.2 dm3. Volumes of gases were measured in STP conditions.
What hydrocarbons were in the starting mixture?
Mr = 2 ×14.4 = 28.8 When reactivity of the hydrocarbons and the value of Mr are taken into consideration then the mixture can only by formed from CH ≡ CH (Mr = 26) and CH3 –CH ≡ CH (Mr = 40).