(a)(i) Give the two reasons why soda lime is used instead of caustic soda in the preparation of methane. (ii) List two physical properties of methane. (iii)...

(a)(i) Soda lime is used instead of caustic soda because:

1. Soda lime does not attack the glass apparatus on heating, whereas caustic soda attacks glass.
2. Soda lime is not deliquescent, whereas caustic soda absorbs moisture from the air and becomes difficult to handle.

(ii) Methane is:

1. a colourless, odourless gas at room temperature;
2. slightly soluble in water and less dense than air.

(iii)

Vapour density = 29.

Therefore, molar mass = \(2 \times 29 = 58\).

Dividing by the smaller value, 6.90:

\[\text{C : H} = 1 : 2.5 = 2 : 5\]

I. Empirical formula = \(\mathrm{C_2H_5}\).

Empirical formula mass = \((2 \times 12) + (5 \times 1) = 29\).

\[n=\frac{58}{29}=2\]

II. Molecular formula = \((\mathrm{C_2H_5})_2 = \boxed{\mathrm{C_4H_{10}}}\).

(b)(i) Isomerism is the existence of two or more compounds having the same molecular formula but different structural formulae, or different arrangements of atoms.

(ii) and (iii) The two isomers of \(\mathrm{C_2H_6O}\) are shown below.

(iv) The isomers have different functional groups and belong to different homologous series. Ethanol is an alkanol containing the hydroxyl group, \(\mathrm{-OH}\), while methoxymethane is an ether containing the \(\mathrm{-O-}\) linkage.

(c) Qualitative and quantitative analysis of an organic compound can be used to deduce:

1. the types of elements present in the compound;
2. the percentage composition, and hence the relative numbers of atoms, of the elements present;
3. the empirical formula and, where the molar mass is known, the molecular formula of the compound.

(d) Pass each gas through bromine water. Propene decolourises the reddish-brown bromine water because it is unsaturated, whereas propane produces no colour change.