(a)(i) What is 2 homologous series? (ii) Give two homologous series present in petroleum (iii) Give one example of a compound belonging to each of the homol...

(a)(i) A homologous series is a family of organic compounds having the same general formula and similar chemical properties, in which successive members differ by a \(\mathrm{CH_2}\) unit.

(ii) Two homologous series present in petroleum are:

1. Alkanes
2. Cycloalkanes

(iii) Examples are:

• Alkane: methane, \(\mathrm{CH_4}\)
• Cycloalkane: cyclohexane, \(\mathrm{C_6H_{12}}\)

(iv) Two fractions obtained from the fractional distillation of petroleum are petrol (gasoline) and kerosene.

(v) There is a gradual change in physical properties because the fractions contain hydrocarbons with gradually increasing molecular masses and carbon-chain lengths. Consequently, the intermolecular forces and boiling points increase from one fraction to the next.

(b)(i) Ethanol with excess concentrated tetraoxosulphate(VI) acid at high temperature:

At about \(170^\circ\mathrm{C}\), ethanol is dehydrated to ethene in two steps:

(ii) Excess ethanol with concentrated tetraoxosulphate(VI) acid at lower temperature:

At about \(140^\circ\mathrm{C}\), diethyl ether is formed in two steps:

(c)(i)(I) Empirical formula

Empirical formula = \(\boxed{\mathrm{C_2H_6O}}\).

(c)(i)(II) Molecular formula

Empirical formula mass = \((2\times12)+(6\times1)+16=46\).

\[n=\frac{\text{relative molecular mass}}{\text{empirical formula mass}}=\frac{46}{46}=1\]

Molecular formula = \((\mathrm{C_2H_6O})_1=\boxed{\mathrm{C_2H_6O}}\).

(c)(ii) Two possible structural formulae of \(\mathrm{C_2H_6O}\)

The first structure is ethanol. The second structure is methoxymethane, also called dimethyl ether.