Which is the simplest alkane?

Test Yourself 12.2 (ALKANES)

  1. No. i. Which is the simplest alkane?

Answer: Methane is the simplest form of alkane.

  1. No. ii. Give the structure of following compounds isopentane, and isobutene

Answer:

      H3C-CH-CH2– CH3      H3C-CH2– CH3 

CH3                               CH3         

           Isopentane                 isobutene

  1. No. iii. Why the burning of alkanes requires sufficient supply of oxygen?

Answer: For complete combustion of alkanes into carbon dioxide sufficient supply of oxygen is required. If there is insufficient supply of oxygen, alkanes will produce carbon monoxide gas, which creates suffocation and causes death Such as;

3CH4 + 4O2 —> 2CO + C+ 6H2O

  1. No.iv. What do you mean by halogenations? Give the reaction of methane with chlorine in bright sunlight.

Answer. A reaction in which one or more hydrogen atoms of saturated compounds are replaced with halogen atoms is called halogenations. Methane reacts in the presence of direct sunlight to form carbon. It is an explosive reaction.

CH4 + 2CI2 ———> C + 4HC1

Test Yourself 12.3 (ALKENES)

  1. No. i. Why alkenes are reactive?

Answer. Alkenes are reactive compounds because the electrons of the double bond are easily available for reaction. These compounds have the tendency to react readily by adding other atoms, to become saturated compounds. As a result, the double bond is converted into a single bond-that is more stable.

  1. No. ii. How can you prepare propene from propyl alcohol?

Answer. Propene is prepared by heating a mixture of propyl alcohol and excess of concentrated sulphuric acid at 180°C. In first step, propyl hydrogen sulphate is formed which on heating .produces propene, which is collected over water.

180 °C

CH3-CH2-CH2OH + H2SO4 ———> CH3– CH2– CH2-OSO3H + H2O

heat

CH3-CH2-CH2OSO3H ———> CH3-HC= CH2 + H2SO4

  1. No.iii. Give a test used to identify unsaturation of an organic compound.

Answer. Unsaturated compounds consist of a double or triple bond. They can be identified by KMnO4 test. Alkenes decolorizes the

3CH2=CH2 + 2KMn04 + 4H2O———> 3H2C——CH2 + 2MnO2 + 2KOH

OH   OH

pink colour of acidified dilute solution of potassium permanganate

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