12 5 This question is about hydrocarbons. (a) Which of these molecular formulae represents a non-cyclic, saturated hydrocarbon? (1) A C6H6 B C6H10 C C6H12 D C6H14 (b) How many structural isomers are there with the molecular formula C5H12? . (1) A 2 B 3 C 4 D 5 (c) How many σ bonds and π bonds are there in one molecule of cyclohexene? . (1) σ bonds π bonds A 5 2 B 6 1 C 15 2 D 16 1 13 Turn over (d) When hydrocarbons undergo complete combustion, there is a change in the total volume of gases. (i) Ethane burns in excess oxygen. 2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(g) All gas volumes are measured at the same temperature and pressure when water is a gas. What is the increase in the total volume when 100 cm3 of ethane is burned in excess oxygen? (1) A 50 cm3 B 100 cm3 C 200 cm3 D 500 cm3 14 (ii) A combustion experiment was carried out using conditions under which water was a liquid. A cyclic hydrocarbon, CxHy , was mixed with excess oxygen and ignited. Under the conditions of the experiment, this hydrocarbon was gaseous and had a volume of 25 cm3. The equation for the complete combustion of CxHy is CxHy(g) + (x + y 4 )O2(g) → xCO2(g) + y 2 H2O(l) The total gas volume decreased by 75 cm3. The remaining gases were shaken with aqueous sodium hydroxide and the total gas volume decreased by a further 125 cm3. All gas volumes were measured at the same temperature and pressure. Suggest the identity of the cyclic hydrocarbon by calculating the molecular formula of CxHy . Include the skeletal formula of the cyclic hydrocarbon. (3) 15 Turn over (e) Propene reacts with iodine monochloride, ICl, by an electrophilic addition mechanism. Draw the mechanism for the reaction between propene and iodine monochloride to form the major product. Include the dipole on the ICl molecule, curly arrows and any relevant lone pairs of electrons. (4) 16 (f) Limonene is obtained from the oil in lemon peel and it is the only alkene present. 0.500 g of the oil reacted with exactly 30.6 cm3 of a solution of bromine dissolved in cyclohexane with a concentration of 0.200 mol dm−3. Calculate the percentage by mass of limonene in the oil. Give your answer to an appropriate number of significant figures. Assume that there is nothing else in the oil that reacts with bromine. (4) (Total for Question 5 = 15 marks) 17 Turn over BLANK PAGE