Question

write one general method of preparation for each of the alkane and alkyne.hiw will you distinguish between ethene and ethyne.​

Answer 1

Answer:

distinguished between ethene and ethyne :

• The two hydrocarbons can be easily distinguished by simple chemical tests, as ethyne molecule is supposed to have acidic hydrogen.

• 1.When ethyne is bubbled through ammoniacal silver nitrate solution , a yellow-white precipitate of silver acetylide would be formed.

• C2H2 + 2AgNO3 = Ag2C2 + 2HNO3

• 2. Similarly, ethyne forms a red precipitate of copper acetylide (Cu2C2) when it is passed through ammoniacal cuprous chloride solution.

• Ethene does not react with AgNO3 or Cu2Cl2 solution.

General methods for preparation of alkanes :

• (1) From unsaturated hydrocarbons :The unsaturated hydrocarbons are converted into alkanes by catalytic hydrogenation in the persence of catalyst such as Ni , Pr etc.

• (2) From alkyl halides : When an alkyl halide is treated with sodium in the presence of dry ether, alkane is obtained. This reaction is called wurtz reaction.

Alkenes can be prepared in 6 methods:

• 1. Reduction of Alkynes (Lindlar/Birch)

• 2. Dehydro-halogenation of Alkyl Halides

• 3. De-halogenation of vicinal Dihalides

• 4. Dehydration of Alcohols

• 5. Kolbe Electrolysis

• 6. Hoffman exhaustive methylation

preparation of alkyne :

• Ethyne, which is commonly called acetylene, is the simplest alkyne. Historically, it was prepared by reacting calcium carbide with water.
• Today, ethyne is normally prepared by the pyrolysis of methane. In this procedure, a stream of methane gas is briefly heated to 1500°C in an airless chamber.