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 formation of CO(g) is -110 kJ mol-1, what is enthalpy change of formation of TiO 2(s)? A -830 kJ mol -1 B +830 kJ mol -1 C -940 kJ mol -1 D +940 kJ mol -1

9 10 The curv e molecules What is a A The d energ B The d energ C The d energ D The d energ Two mol e partly deco and L was At equilibr was (2+x) A J B 2J C 2J D 2J e Y and t h s and the a possible o distribution gy by value distribution gy by value distribution gy by value distribution gy by value es of com p omposed b s establishe rium, x mo . What is th 2K + L 2K + L K + L K + 2L he value E ctivation e utcome if t n of energ e V. n of energ e V. n of energ e W. n of energ e W. pound J w by heating ed. l of L were he equatio L L 5 Ea repres e energy for a the reactio ies will b e ies will b e ies will b e ies will b e were place d . A dynam e present a on for this e nt the dis t an uncataly on is cataly e given by e given by e given by e given by d in a ve s ic equilibri and the tot equilibrium tribution o ysed gase sed? curve X a curve Y a curve Y a curve Z a ssel. The c um betwee al number ? of energie s ous reactio and the a c and the a c and the a c and the a c compound en chemica r of moles s of the on. ctivation ctivation ctivation ctivation d J was als J, K present

6     11 Bromine is formed by t he reaction between bromate(V) ions and bromide ions and acid: BrO3 - (aq) + 5Br - (aq) + 6H+ (aq)  3Br2 (aq) + 3H2O (l) The results of some experiments on the reaction are shown below. Experiment Concentration / mol dm-3 Initial rate / mol dm-3 s-1 BrO3 - Br - H + 1 0.10 0.10 0.10 1.2 x 10 -3 2 0.10 0.30 0.10 3.6 x 10 -3 3 0.20 0.10 0.10 2.4 x 10 -3 4 0.20 0.10 0.20 9.6 x 10 -3 Which statement is true based on the above data? A The overall order of reaction is three. B The rate of reaction is independent of [BrO 3 -]. C The unit of the rate constant is mol -3 dm9 s-1. D The time taken for the concentration of Br - to decrease to half its initial value is the same for Experiment 1 to 4.  12 Citric acid is a monobasic acid. Which of the following pair of solutions, when mixed at equal volume, will give a best buffer solution that resists a pH change when a small amount of acid or base is added? A 0.5 mol dm -3 of citric acid and 0.5 mol dm-3 of NaOH B 0.5 mol dm -3 citric acid and 0.125 mol dm-3 of Ba(OH)2 C 1.0 mol dm -3 sodium citrate and 0.25 mol dm-3 of H2SO4 D 1.0 mol dm -3 sodium citrate and 0.5 mol dm-3 of H2SO4

7     13 A dilute solution of hydrogen peroxide decomposes slowly in aqueous solution according to the following equation: 2H2O2(aq) → 2H2O(l) + O2(g) A solution with an original concentration of 3.00 mol dm -3 was placed in a bottle contaminated with transition metal ions, which act as catalyst for the decomposition. The rate of decomposit ion was measured by withdrawing 10.0 cm 3 portion at various times and titrating with acidified 0.05 mol dm -3 KMnO4(aq). The following results were obtained. How long has the solution in the bottl e been contaminated before the first portion was withdrawn for titration? Assume that 5 mol H2O2 reacts with 2 mol KMnO4. A 14 minutes B 42 minutes C 84 minutes D 112 minutes 0 5 10 15 20 25 30 0 5 10 15 20 25 30 Volume of KMnO4(aq) / cm3 Time / min

8     14 Which of the following statement is correct for the sequence of compounds below considered from left to right? NaF MgO A lN SiC A The bonding becomes decreasingly covalent. B The formula-units of these compounds are not isoelectronic. C Electronegativity difference betw een the elements in each compound decreases. D When water is added to these compounds, the resultant solution becomes increasingly acidic. 15 An element X in Period 3 is a metalloid and semiconductor and has a chloride which reacts with water to form an acidic solution. An element Y has an atomic number one less than element X. What is a property of the oxide of element Y? A It is a gas at room temperature. B It is amphoteric. C It is covalent. D Its formula is YO2. 16 The information relates to element Z.  Z is in Period 3 of the Periodic Table.  Z has a lower electrical conductivity than Mg.  A Z atom has half-filled subshell in its ground state.  Z forms an acidic oxide on exposure to air. What is Z? A Na B Si C P D C l

9     17 Ethoxyethane, C 2H5OC2H5, is the most well known of a class of compounds called ethers. Ethers have the general formula R1–O–R2 where R1 and R2 are hydrocarbon groups. How many structural isomers does ethoxyethane have? A 2 B 3 C 6 D 7   18 Cholesterol is the most common steroi d alcohol. It has a molecular formula of C27H46O and has the structure shown. How many carbon atoms are in the hydrocarbon group R? A 7 B 8 C 9 D 10 19 Experiments are carried out on three compounds X, Y, and Z