18   5 A student found a bottle of a colourless liquid that was thought to be an alcohol. However, the label was missing and the identity of the alcohol was unknown. The student decided to attempt to identify this alcohol (Q) by measuring its enthalpy change of combustion, and comparing the result with values in a data book. The student used the equipment shown in the diagram to determine the enthalpy change of combustion of alcohol Q. thermometer beaker water spirit burner alcohol Q Data Mass of spirit burner + alcohol Q before combustion = 20.24 g Mass of spirit burner + alcohol Q after combustion = 19.48 g Mass of water in the beaker = 500 g Temperature of the water before the experiment = 17.8 °C Temperature of the water at the end of the experiment = 28.7 °C Specific heat capacity of water = 4.18 J g–1 °C–1 Turn over 19   (a) (i) Calculate the enthalpy change, in kJ g–1, when 1.00 g of alcohol Q is burned. Include a sign in your final answer. (3) (ii) At the end of the experiment there was a black deposit of carbon on the bottom of the beaker. Explain the effect of formation of the carbon deposit on your answer to (a)(i). (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 20   (b) Give one theoretical and one practical reason why this procedure is insufficient to identify the alcohol. (2) Theoretical reason .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... Practical reason .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (c) The student concluded that alcohol Q was either propan‑1‑ol or propan‑2‑ol because the mass spectrum had the molecular ion peak at m / z = 60. Explain one peak that you would expect to be present in the mass spectrum of propan‑1‑ol but not in the mass spectrum of propan‑2‑ol. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question 5 = 9 marks) Turn over 21   6 Ammonium carbamate has the formula NH2COONH4 . When a sample of ammonium carbamate is placed in a sealed tube and heated, it partially decomposes to the compounds used to synthesise it. The equation for this reversible reaction is NH2COONH4(s)  2NH3(g) + CO2(g) Which is the expression for the equilibrium constant, Kc , for this reaction? All concentration terms are at equilibrium. A NH CO NH COONH4 3 2 2 B 2NH CO NH COONH4 3 2 2 C NH CO 3 2 2 D NH CO NH COONH4 3 2 2 2 (Total for Question 6 = 1 mark)