Write a detailed note on functional groups of alkenes and alkynes. How they are identified from other compounds?

  1. No.3. Write a detailed note on functional groups of alkenes and alkynes. How they are identified from other compounds?

Answer.   Organic   compounds   containing   double   bond   in   their molecules are called alkenes, such as:

H2C = CH2

Ethene

Organic compounds containing triple bond in their molecules are called alkynes, such as:

HC ≡ CH

Ethene (Acetylene)

 

Identification from other compounds

(i)      Bromine water test:

Dissolve a pinch of the given organic compound in 2.0cm3 of carbon tetrachloride (CCI4). Add 2cm3 of bromine water in it. Bromine will be decolorized which confirms the presence of double or triple bond.

(ii)     Baeyer’s test:

Dissolve about 0.2 g of the organic compound in water. Add 2-3 drops of alkaline KMnO4 solution in the aqueous solution of organic compound. Pink colour will disappear. This confirms the presence of double or triple bond.

  1. No.4. Give some uses of organic compounds in our daily life.

Answer. The main uses of organic compounds in daily life are

  1. Uses as Food: The food we eat daily such as milk, eggs, meat, vegetables, etc., contain carbohydrates, proteins, fats, vitamins, etc., are all organic compounds.
  1. Uses as Clothing: All types of clothing (we wear, we use as bed sheets etc.) are made up of natural fibers (cotton, silk and wool, etc.) and synthetic fibers (nylon, Dacron and acrylic, etc.) all these are organic compounds.
  1. Uses as Houses: Wood is cellulose (naturally synthesized organic compound). It is used for making houses and furniture of all kinds. All of these are organic compounds.
  2. Uses as Fuel: The fuels we use for automobiles and domestic purposes are coal, petroleum and natural gas. These are called fossil fuels. All of these are organic compounds.
  3. Uses as Medicines: A large number of organic compounds (naturally synthesized by plants) are used as medicines by us. Most of the life saving medicines and drugs such as antibiotics (inhibit or kill microorganisms which cause infectious diseases) are synthesized in laboratories.
  1. Uses as Raw Material: Organic compound are used to prepare a variety of materials, such as rubber, paper, ink, drugs, dyes, paints, varnishes, pesticides, etc.
  1. No.5. Write down the characteristics of homologous series. Answer.
  • All members of a series can be represented by a general formula for example, general formula of alkane, alkenes and alkynes are CnH2n +2, CnH2n and CnH2n -2 respectively.
  • Successive members of the series differ by one unit of -CH2– and a mass of 14 amu.
  • They have similar chemical properties because they contain the same functional group.
  • There is a regular change in their physical properties; the melting and boiling points increase gradually with the increase of molecular masses.
  • They can be prepared by similar general methods.

Hydrocarbons are regarded as parent organic compounds. All other   compounds   are   considered   to   be   derived   from   them   by substituting one or more hydrogen atoms of a hydrocarbon by one more reactive atom or group of atoms.

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