SAJC H2 Chem 2013 Prelim P1 Soln

20     [Turn Over   1 B 11 A 21 C 31 D 2 C 12 A 22 C 32 D 3 B 13 C 23 A 33 D 4 C 14 C 24 A 34 D 5 B 15 C 25 B 35 B 6 C 16 A 26 D 36 C 7 A 17 A 27 B 37 A 8 D 18 C 28 A 38 D 9 D 19 C 29 A 39 C 10 B 20 D 30 C 40 B 1130

1 [Turn Over Worked Solutions for SAJC 2013 Prelim Exam Paper 1 1 The metal, M (Ar = 52.8), combines with 1.2 g of oxygen to form the oxide M2O. The metal, M, also forms a second oxide in which the metal and oxygen are present in the ratio 14:1 by mass. What is the molecular formula of the second oxide? A M2O3 B M4O C M11O3 D M7O In M2O For 2nd oxide, assuming 15g of oxide, 1 g of O = 0.0625 mol 14 g of M = 0.265 mol Ratio of M:O is 0.265:0.0625 /barb2right/barb2right /barb2right/barb2right 4.24:1 Ratio is 4.24:1. Ans: B 2 0.0100 mol of an oxide of an element, L, represented by L2On is found to react with exactly 8. 00 x 10I3 mol of acidified KMnO 4 solution. In the reaction, aqueous H LO4 2I ion is formed. Wh at is the initial oxidation state of L? A + 1 B + 2 C + 3 D + 4 L is oxidised to HLO4 2R, MnO4 R is reduced. L loses electrons. Amt of KMnO4 used = 8.00 x 10R3 mol Am t of electrons donated by L = 0.04 mol Amt of L atoms = 0.01 x 2 = 0.02 mol Ratio of electrons donated : L is 0.04:0.02 /barb2right/barb2right /barb2right/barb2right 2:1 Each L has its oxidation state increased by +2. L has final oxidation state of 5+ in HLO4 2R, so initial oxidation state should be +3. An s: C 1131

2 [Turn Over V V PV P P Density 3 Which of the following diagrams correctly describes the behavior of a fixed mass of an ideal gas at constant T? (T is measured in K.) A C B D Ans: B. PV = nRT, so for a fixed mass of gas, the value of nRT is constant and does not change on the graph regardless of the value of V. 4 With reference to its electronic configuration, which of the following statements is true about the electrons in the atoms of the element with atomic number 29? A The electrons in the outermost principle quantum shell experience interIelectronic repulsion. B The d electrons are in the same principle quantum shell as the outermost s electrons. C There are p electrons in 2 different principle quantum shells. D There are s electrons in 3 different principle quantum shells. Element with atomic number 29 is copper Cu. A is not true because the only electrons in the outermost principal quantum shell are the 4s electrons – there is no interRelectronic repulsion in 4s orbital. B is not true as the electrons are in 3d and 4s orbitals. C is true as there are electrons in the 2p and 3p subshells. D is not true as there are electrons in the 1s, 2s, 3s, and 4s subshells. Ans: C 1132

3 [Turn Over 5 The graph shows the logarithm, lg, of the first eight ionisation energies of two elements in Periods 2 and 3. What is the most likely compound that will be formed between the two elements? A CO2 B SiO2 C