Hydrocarbons (For Grade 10 Students)

Question 1. Define hydrocarbons.

Answer. The organic compounds which contain only carbon and hydrogen are called hydrocarbons.

Question 2. What are alkanes?

Answer. The saturated hydrocarbons which have all single bonds are called alkanes.

OR the hydrocarbons which have general formula CnH2n+2 are called alkanes. In alkanes, each carbon forms four single bonds and hydrogen forms one bond. For example, CH4, C2H6, C3H8 etc

Question. Draw structural formula of methane, ethane and propane.

Solution

Methane

Ethane
Propane

For practice

Question

Draw structure of following compounds. 1. Butane 2. Pentane 3. Hexane 4. Heptane 5. Octane 6. Nonane 7. Decane

Solution

Question. Draw electron dot and cross structures for ethane.

Solution

Self-Assessment Exercise 12.2 Draw electron dot and cross structures for following.

a. Propane b. Butane

Solution

For practice

Question. Draw dot and cross structure of following compounds: a. Pentane b. Hexane c. Heptane d, Octane e. Nonane f. Decane

Solution

General method of preparation of Alkanes

1.By hydrogenation of alkenes and alkynes Addition of hydrogen molecule across carbon-carbon multiple bonds is called hydrogenation. Hydrogenation takes place in the presence of finally divided nickel at temperature of 200 to 300 oC and high pressure. Hydrogenation can also be done in presence of Pt or Pd at room temperature.

By Reduction of alkyl halides Addition of hydrogen is called reduction. An alkane can be produced by reduction of alkyl halide with Zinc in the presence of aqueous acid such as aqueous solution of HCl or CH3COOH.

Atomic hydrogen also known as nascent hydrogen is produced when zinc reacts with aqueous acid. Nascent hydrogen reduces alkyl halide.

Self-Assessment

12.3 Question complete the following hydrogenation reactions

12.4 Question complete the following reduction reactions

Solutions 12.3 & 12.4

Page 2

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