2013_MJC_H1_Chemistry_QP with answer

2   ©MJC Chemistry  2013 MJC H1 Prelim Paper 1 QP and Answers 1 The polyoxometallate W 72Mn12Si7O268 40- was recently ident ified in a crystal garden. Which row gives oxidation states of tungsten and manganese that are consistent with this formula? oxidation state of tungsten oxidation state of manganese A +3 +2 B +3 +3 C +6 +2 D +6 +3 2 Copper ( II) ions react with iodide ions to release iodine as shown in the following equation. 2Cu2+ + 4I-  2CuI + I2 The iodine released can be determi ned by titration using a standardised solution of sodium thiosulfate. The equat ion for this reaction is shown below, 2 S 2O3 2- + I2  S4O6 2- + 2I- 25.00 cm 3 of a solution containing copper ( II) ions was treated with excess iodide ions. The resulti ng iodine required 26.50 cm 3 of sodium thiosulfate of concentration 0.150 mol dm-3 for complete reaction. What was the concentration of copper (II) ions in the solution used? A 0.0795 mol dm-3 B 0.0912 mol dm-3 C 0.159 mol dm-3 D 0.318 mol dm-3

3     3 In a reaction, 0.20 mol of an oxide, N xOy was reacted with 20 dm3 of hydrogen gas at room temperature and pressure and passed over a heated catalyst. At the end of the reaction, 0.80 dm 3 of hydrogen gas remained. The ammonia produced required 0.200 mol of sulphuric acid for complete neutralisation. The reaction of the oxide with hy drogen can be represented by the following equation: N xOy (g) + 32 2 xy H2 (g)  x NH3 (g) + y H2O (l) What is the molecular formula of the oxide? A NO B NO 2 C N2O D N 2O4 4 Which compound is composed of a cation and anion(s) that do not contain the same number of electrons as each other? A LiH B NaOH C NH4F D TiCl3 5 The ionic radius of the elements in Period 3 (Na to C l) changes across the period. Which of the following statements does not explain the trend of the ionic radius across the period? A Across the period, there is an increase in the nuclear charge. B The anions have greater shielding effect than the cations. C Screening effect is approximately constant among the cations. D The effective nuclear charge decreases from P3- to Cl-.

4     6 Which of the following stat ements describe a phenomenon which cannot be explained by hydrogen bonding? A Ice floats on water. B The boiling point of methanol is lower than that of ethanol. C Ethanal dissolves in water. D Ethanoic acid molecules form dimers when dissolved in benzene. 7 A covalent molecule contains  14 electrons,  one lone pair of electrons,  two  bonds. What is the molecule? A C2H4 B HCN C H2O2 D N2 8 Titanium occurs naturally as the mineral rutile, TiO 2. One possible method of extraction of titanium is to reduc e the rutile by heating with carbon. TiO2(s) + 2C(s)  Ti(s) + 2CO(g) ∆H = +720 kJ mol-1 Given that the enthalpy change of fo