(a) i) An organic compound X contains 40% carbon, 6.67% hydrogen, the rest being oxygen. If X has a relative molecular mass of 60, determine its
(i) empirical formula (ii) molecular formula. [H = 1 ; C = 12; O = 16]
(b) An alkanoic acid Y has a relative molecular mass of 74.
(i) State the functional group of Y
(ii) What t of reaction is involved when Y is converted to an alkanoate?
(iii) Determine the structural formula of Y.
(iv) Write an equation for the reaction between Y and sodium
(v) If X in (a) above boils at 118°C and belongs to the same homologous series as Y, state with reason, whether the boiling point of Y will be equal to, higher or lower than 118°C.
(c)(i) What is fermentation?
(ii) Write an equation for the fermentation of glucose.
(iii) What must be added to glucose solution to make it ferment?
(iv) Explain why a tightly corked grass bottle filled to the brim with fresh palm wine shatters on standing.
Explanation
(a)(i) X contains 40% carbon, 6.67% hydrogen, the rest being oxygen. To determine the empirical formula of X
(i) Percentage oxygen = 100 – (40 + 6.67) = 53.33%
C : H O
40 6.67 53.33
12 1 16
3.33 6.67 3.33
1 2 1
Ratio
Empirical formula is CH\(_2\)O
(ii) Molecular formula of X if its relative molecular mass is 60. (CH\(_2\)O)\(_n\) = 60;
(12 + 2 + 16)\(_n\) = 60 ;
30n = 60 ; n = 2
Molecular formula is C\(_2\)H\(_4\)O\(_2\)
(b) Y is an alkanoic acid with relative molecular mass is 74.
(i) The functional group in Y is –COOH/carboxyl group.
(ii) Esterification reaction
(iii) If Y is represented by C\(_n\)H\(_{2n+1}\)COOH; then 14n + 46 = 74, giving n = 2
(iv) 2C\(_2\)H\(_5\)COOH + 2Na –> 2C\(_2\)H\(_5\)COONa + H\(_2\).
(v) Compound Y in the same homologous series as X has a CH\(_3\)CH\(_2\)COOH relative molecular mass of 74. The boiling point of Y will be N higher. than 118° because in a homologous series boiling OH point increases with increase molar mass.
(c)(i) Fermentation is the breakdown of carbohydrates (sugars) to form ethanol (alcohol) and CO\(^2\) by the action of enzymes.
(iii) Yeast is added to glucose solution to make glucose ferment.
(iv) A tightly caked glass bottle filled to the brim with fresh palm wine shatters.on standing because CO\(^2\) is produced as the palm wine ferments. The gas causes pressure build-up which causes the bottle to shatter.