O-LevelChemistryStoichiometry5070/22 · May/June 2014 · Q810 Marks

Butan-1-ol, CH3CH2CH2CH2OH, and ethanol, CH3CH2OH, are both alcohols. Alcohols, such as ethanol, react with sodium to form hydrogen. 2CH3CH2OH + 2Na → 2CH3CH2ONa + H2

(a)Construct the equation to show the reaction of butan-1-ol with potassium. .[1][1]
(b)Describe the chemical test for hydrogen. .[1][1]
(c)A sample containing 0.233 g of an unknown Group I element is added to excess ethanol. The volume of hydrogen gas formed at room temperature and pressure is 400 cm³. Calculate the relative atomic mass, Ar, of the Group I element and suggest the identity of the element. relative atomic mass = identity of the element = ....[4][4]
(d)Ethanol reacts with ethanoic acid to make an organic compound. Draw the structure, showing all the atoms and all the bonds, of this organic compound. [1][1]
(e)Describe the manufacture of ethanol starting from glucose. Include an equation and the conditions needed. [3][3]

Mark scheme

Marking points from the official mark scheme (May/June 2014). The mark or mark type is shown in brackets.

[1] B8 (a) 2CH3CH2CH2CH2OH + 2K → 2CH3CH2CH2CH2OK + H2 (1) ALLOW: any correct multiple / fraction IGNORE: state symbols
[1] (b) Pops with lighted splint / (small) explosion with lighted splint (1)
[1] (c) Moles of hydrogen = 400/24000 = 0.01667 (1) (mark for working or correct answer)
[1] (c) Moles of alkali metal = 0.01667 × 2 = 0.03334 (1) (mark for working or correct answer)
[1] (c) Ar = 7 (1)
[1] (c) Lithium / Li (1) ALLOW: appropriate answer based on incorrect Ar in step 3
[1] (d) [Structure for ethyl ethanoate] H O H H | || | | H–C–C–O–C–C–H | | | | H H H H (1)
[1] (e) C6H12O6 → 2CO2 + 2C2H5OH (1) IGNORE: state symbols
[1] (e) Any two (1 mark each) from: Yeast Warm / quoted temperature of 20–45°C Absence of air / absence of oxygen / anaerobic pH neutral / pH near neutral Distil to get final product
[1] (e) (Second condition for fermentation)

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