Question 22
(a) Propanone can be formed when glucose comes into contact with bacteria in the absence of air.
(i) Balance the following equation for this reaction of glucose to form propanone, carbon dioxide and water.
…….C6H12O6 –> …….CH3COCH3 + …….CO2 + …….H2O
(1)
(ii) Deduce the role of the bacteria in this reaction.
(1)
(b) Propanone is also formed by the oxidation of propan−2−ol.
(i) Write an equation for this reaction using [O] to represent the oxidising agent.
(1)
(ii) State the class of alcohols to which propan−2−ol belongs.
(1)
(c) A student determined a value for the enthalpy change when a sample of propanone was burned. The heat produced was used to warm some water in a copper calorimeter.
The student found that the temperature of 150 g of water increased by 8.0 °C when 4.50 × 10−3 mol of pure propanone was burned in air.
Use the student’s results to calculate a value, in kJ mol−1, for the enthalpy change when one mole of propanone is burned.
(The specific heat capacity of water is 4.18 J K−1 g−1)
(3)
(d) Define the term standard enthalpy of combustion.
(3)
(e) Use the mean bond enthalpy data in the table and the equation given below the table to calculate a value for the standard enthalpy change when gaseous propanone is burned.
CH3COCH3(g) + 4O2(g) –> 3CO2(g) + 3H2O(g)
(3)
(f) Suggest two reasons why the value obtained by the student in part (c) is different from the value calculated in part (e).
(2)
(Total 15 marks)