Alkanes Questions & Answers on Organic Chemistry

1. Select the incorrect statement regarding alkanes.

a) It is otherwise known as Paraffin
b) It is an acyclic saturated hydrocarbon
c) In alkanes, C-C bonds are single
d) Alkanes have the general formula CnH2n

Answer: d

Explanation: Alkanes have the general formula CnH2n+2, i.e; they have two additional hydrogen atoms in comparison with the others.

2. Identify the simplest alkane.

a) Methane
b) Methene
c) Ethane
d) Ethene

Answer: a

Explanation: Methane, called the parent molecule, is the simplest among the alkanes and it has the simplest formula with one carbon atom.

3. Select the minimum number of carbon atoms, a molecule must possess so as to be regarded as a higher alkane.

a) 15
b) 16
c) 17
d) 18

Answer: c

Explanation: A molecule with more than 17 carbon atoms are regarded as higher alkanes such as waxes and solids.

4. Identify the incorrect statement.

a) Alkanes with repeated –CH2– units constitute a homologus series
b) They are very reactive
c) They have very less biological activity
d) Petroleum and natural gas are the main sources of alkanes

Answer: b

Explanation: Alkanes in general are not very reactive, but they are associated with functional groups which are reactive.

5. Which among the following is not an alkane isomer with 6 carbon atoms?

a) Hexane
b) 2,3-dimethylbutane
c) 2,2-dimethylbutane
d) Neopentane

Answer: d

Explanation: Neopentane is an isomer with 5 carbon atoms and hence it is not an isomer with 6 carbon atoms.

6. The other name for branched chain alkanes is ______

a) Paraffins
b) Isoparaffins
c) Neoparaffins
d) Naphthenes

Answer: b

Explanation: Linear and branched chain alkanes have difference in their physical properties and hence they are given different prefix like n- and iso-respectively.

7. Select the incorrect statement regarding the boiling points of alkanes.

a) Boiling point increases with stronger Vander Waal’s forces
b) Surface area is the only factor which determines the boiling point of alkane
c) Boiling point of straight chain alkanes is greater than that of branched chain alkanes
d) The boiling point of cycloalkanes is always higher than that of linear alkanes

Answer: b

Explanation: Number of electrons and surface area are the two factors which determine the boiling point.

8. Choose the correct statement.

a) Alkanes have poor conductivity
b) They form hydrogen bonds
c) They have good solubility in non polar solvents than polar solvents
d) Alkanes have less density than that of water

Answer: b

Explanation: They undergo polarization and hence they do not form hydrogen bonds.

9. Liquified petroleum gas is mainly composed of ______

a) Methane and ethane
b) Ethane and propane
c) Propane and butane
d) Butane and hexane

Answer: c

Explanation: At low pressure both propane and butane gets liquefied, hence they form the main components of LPG.

10. An alkane with 6 carbon atoms will have how many hydrogen atoms?

a) 11
b) 12
c) 13
d) 14

Answer: d

Explanation: From the formula CnH2n+2, if n = 6 then (2 × 6)+2 = 14. Hence 6 carbon atoms will have 14 hydrogen atom.

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