(a) List three characteristics of a homologous series
(b) Give one example of;
(i) alkanes; (ii) alkynes.
(c) A hydrocarbon contains 7.7% by mass of hydrogen and 92.3% by mass of carbon. The relative molar mass of the compound is 78.
(i) Derive the empirical formula of the compound and hence its molecular formula.
(ii) Name the hydrocarbon and write its structural formula. (H=1, C=12)
(d) Two hydrocarbons, X and Y were treated separated with acidified potassium tetraoxomanganate (VII) solution. X decolorized the solution and Y did not. Which of X and Y will undergo
(i) substitution reaction only,
(ii) both addition and substitution reactions.
(iii) polymerization?
(e) If ethanol is to be converted into ethanoic acid
(i) What are the conditions required?
(ii) name the type of reaction that will be involved and write the equation
Explanation
(a) Members of a homologous series can be prepared by the same method. Members exhibit the same general chemical reaction. The molecular formula of each member of a homologous series can be derived from a general formula.
(b)(i) Hexane (CH\(_3\)CH\(_2\)CH\(_2\)CH\(_2\)CH\(_2\)CH\(_3\))CH = CH(ethyne)
(c)(i) moles H = \(\frac{7.7}{1.0}\) = 7.7 moles
moles C = \(\frac{92.3}{12}\) = 7.7 moles
i.e \(\frac{7.7}{7.7}\) H ; \(\frac{7.7}{7.7}\) C = 1 : 1
Empirical formula of the hydrocarbon is CH
(CH)x = 78; (13)x = 78;
x = \(\frac{78}{13}\) = 6
Molecular formula is C\(_6\)H\(_6\)
(ii) The molecule is Benzene. The structure is
(d)(i)Y undergoes substitution reaction only.
(ii) x (iii) x H L
(e)(i) Suitable catalyst must be applied when reacted directly with air. In another method, acidified suitable oxidising agent must be applied.
(ii) Oxidation reaction CH\(_3\)CH\(_2\)OH\(_{(g)}\) + CH\(_2\)COOH\(_{(l)}\) +H\(_2\)O\(_{(g)}\)