(a)(i) What is meant by hydrocarbons?
(ii) A hydrocarbon consists of 92.3% carbon. If it’s vapour density is 39, determine its molecular formula. (H = 1; C = 12)
(b)(i) Outline a suitable laboratory procedure for obtaining ethanol from cassava tubers
(ii) List two laboratory reagents used for oxidizing ethanol to ethanoic acid.
(c) What name is given to each of the following processes?:
(i) Conversion of alkanols to alkanoates;
(ii) Breakdown of proteins to amino acids;
(iii) Conversion of oils to fats
(iv) Alkaline hydrolysis of fats and oils.
Explanation
i) Hydrocarbons are compounds consisting of carbon and hydrogen only.
(ii) H = (100 - 92.3)% = 7.7%
C : H
\(\frac{92.3}{12}\) : \(\frac{7.7}{1}\)
\(\frac{7.7}{1}\) : \(\frac{7.7}{1}\)
Therefore, the empirical formula is CH, hence the molecular formula is (CH)n.
Molar mass = 2 x vapour
Density = 2 x 39 = 78;
(CH)n = 13n = 78,
:. n = \(\frac{78}{13}\) = 6 13 Therefore, the molecular formula is C\(_6\)H\(_6\).
(b)(i) The cassava is crushed and pressure cook to extract starch granules. Treat with malt which contains diastase to convert the starch to maltose. Add yeast and leave to ferment for about two days. The maltose in yeast coriverts the maltose into glucose. The zymase also in yeast converts the glucose into ethanol and carbon (iv) oxide. Distil to obtain ethanol from the "wash"
(ii) Acidified potassium tetraoxomanganate (VII) and acidified potassium heptaoxodichromate (VI)
(c)(i) Esterification (ii) Hydrolysis (iii) Hydrogenation (iv) Saponification