1. Calculate the mean relative atomic mass of nickel from the mass spectrum. (Marks available: 2) Answer Answer outline and marking scheme for question: 1 Intensities of peaks: 58Ni = 10.2 = 69.4% of total (abundance) 59Ni = 3.9 = 26.5% of total (abundance) 62Ni = 0.6 = 4.1% of total (abundance) (Sum of intensities = 14.7) Mean relative atomic mass = (58 x 69.4) + (59 x 26.5) + (62 x 4.1) = 58.4 100 (Marks available: 2) 2. In 1774 Joseph Priestly conducted one of his most famous experiments which lead to a method for the preparation of oxygen. The experiment involved heating a sample of mercury II oxide with a large lens. The equation for this reaction is shown below: 2HgO(s) = 2Hg(l) + O2(g) a) What volume of O2(g) would be obtained if 1.08g of mercury II oxide were completely decomposed? (Given that 1 mole of a gas occupies 24 dm3 under the experimental conditions) (Marks available: 3) Answer Answer outline and marking scheme for question: 2 Molar mass of HgO = 201 + 16 = 217 gmol-1 1.08g of HgO will contain 1.08 / 217 mols = 0.005mol From the equation, 1 mole of O2(g) is produced from 2 moles of HgO This means that 0.005 mol of HgO will produce 0.005 / 2 mol of O2 = 0.0025 mol 0.0025 mol of O2 will occupy 0.0025 x 24dm3 = 0.06dm3 (Marks available: 3) 3. An organic compound is found to have the following composition by mass: C 72.7%; H 6.1%; N 21.2%. a) Calculate the empirical formula of the compound. (2 marks) b) The molar mass of the compound is 198 gmol-1. Calculate the molecular formula of the compound. (3 marks) (Marks available: 5) Answer Answer outline and marking scheme for question: 3 Ratio of elements in compound C : H : N Ratio C : N : H = 72.7 / 12 : 6.1 / 1 : 21.2 / 14 = 6.1 : 6.1 : 1.5 Whole number ratio = 4 : 4 : 1 Empirical formula of compound is C4H4N (Marks available: 5)