(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.
(a) Empirical and molecular formula of X (40% C, 6.67% H, O = 100 - 40 - 6.67 = 53.33%)
| Element | C | H | O |
|---|
| Moles | 40/12 = 3.33 | 6.67/1 = 6.67 | 53.33/16 = 3.33 |
| Ratio (÷ 3.33) | 1 | 2 | 1 |
(i) Empirical formula = CH2O (mass = 30).
(ii) \(\dfrac{60}{30}=2\), so molecular formula = C2H4O2.
(b) Alkanoic acid Y, Mr = 74. For CnH2n+1COOH, propanoic acid C2H5COOH has Mr = 74.
(i) Functional group: carboxyl group, -COOH. (ii) Converting Y to an alkanoate (salt) is a neutralization reaction. (iii) Structural formula of Y: CH3CH2COOH. (iv) 2CH3CH2COOH + 2Na → 2CH3CH2COONa + H2.
(v) X (C2H4O2) is ethanoic acid; Y is propanoic acid, in the same homologous series. Y has a larger relative molecular mass (74 > 60) and longer chain, so stronger van der Waals forces; its boiling point will be higher than 118°C.
(c)(i) Fermentation is the slow chemical breakdown of a complex organic substance (such as sugar) into simpler substances (ethanol and carbon(IV) oxide) by the action of enzymes from micro-organisms such as yeast. (ii) C6H12O6 → 2C2H5OH + 2CO2. (iii) Yeast (which supplies the enzyme zymase) must be added. (iv) The palm wine keeps fermenting and produces carbon(IV) oxide gas; because the bottle is full to the brim and tightly corked, the gas cannot escape, so the pressure builds up until it exceeds the strength of the bottle and it shatters.
(a) Empirical and molecular formula of X (40% C, 6.67% H, O = 100 - 40 - 6.67 = 53.33%)
| Element | C | H | O |
|---|
| Moles | 40/12 = 3.33 | 6.67/1 = 6.67 | 53.33/16 = 3.33 |
| Ratio (÷ 3.33) | 1 | 2 | 1 |
(i) Empirical formula = CH2O (mass = 30).
(ii) \(\dfrac{60}{30}=2\), so molecular formula = C2H4O2.
(b) Alkanoic acid Y, Mr = 74. For CnH2n+1COOH, propanoic acid C2H5COOH has Mr = 74.
(i) Functional group: carboxyl group, -COOH. (ii) Converting Y to an alkanoate (salt) is a neutralization reaction. (iii) Structural formula of Y: CH3CH2COOH. (iv) 2CH3CH2COOH + 2Na → 2CH3CH2COONa + H2.
(v) X (C2H4O2) is ethanoic acid; Y is propanoic acid, in the same homologous series. Y has a larger relative molecular mass (74 > 60) and longer chain, so stronger van der Waals forces; its boiling point will be higher than 118°C.
(c)(i) Fermentation is the slow chemical breakdown of a complex organic substance (such as sugar) into simpler substances (ethanol and carbon(IV) oxide) by the action of enzymes from micro-organisms such as yeast. (ii) C6H12O6 → 2C2H5OH + 2CO2. (iii) Yeast (which supplies the enzyme zymase) must be added. (iv) The palm wine keeps fermenting and produces carbon(IV) oxide gas; because the bottle is full to the brim and tightly corked, the gas cannot escape, so the pressure builds up until it exceeds the strength of the bottle and it shatters.
