Explain the processes of fractional distillation and cracking of hydrocarbons, including necessary conditions, equations, and isomers.

Here are the answers to your questions:

1. • a) Petrol is a mixture of several alkane molecules ranging from pentane ($\text{C}_{5}\text{H}_{12}$) to decane ($\text{C}_{10}\text{H}_{22}$). Name the process by which petrol is obtained from crude oil. (1mk)

     • Fractional distillation

   • b) A decane molecule derived from petrol is cracked into hydrocarbon with equal number of carbon atoms in each molecule.

     • i) What is cracking? (1mk) Cracking is the process of breaking down large, long-chain hydrocarbon molecules into smaller, more useful short-chain hydrocarbons (alkanes and alkenes).

     • ii) State two conditions necessary for the above process. (2mks)

       • i) High temperature (heat)
       • ii) Catalyst (e.g., aluminium oxide, silicon dioxide)

     • iii) Write an equation for the cracking of decane molecule. (1mk)

       $$\text{C}_{10}\text{H}_{22} \longrightarrow \text{C}_{5}\text{H}_{12} + \text{C}_{5}\text{H}_{10}$$

       (Decane $\longrightarrow$ Pentane + Pentene)

     • iv) Draw and name two isomers of molecules with lower molecular mass obtained from cracking of decane as shown in b) (iii) above. (2mks) The products with lower molecular mass are pentane ($\text{C}_{5}\text{H}_{12}$) and pentene ($\text{C}_{5}\text{H}_{10}$). Here are two isomers of pentane:

       • 1. n-pentane
         $$\text{CH}_{3}\text{CH}_{2}\text{CH}_{2}\text{CH}_{2}\text{CH}_{3}$$
       • 2. 2-methylbutane
         $$\text{CH}_{3}\text{CH}(\text{CH}_{3})\text{CH}_{2}\text{CH}_{3}$$

   • c) Give the IUPAC name of the following compounds:

     • i) $\text{CH}_{3}\text{CH}(\text{CH}_{3})\text{CHBrCH}_{3}$ (1mk)

       • 2-bromo-3-methylbutane

     • ii) $\text{CHCCH}_{2}\text{CH}_{3}$ (1mk) (Assuming the structure is $\text{CH}\equiv\text{CCH}_{2}\text{CH}_{3}$)

       • But-1-yne