SAJC Prelim P1_ANS

1 [Turn Over SAJC Prelim 2015 H2 Chemistry Paper 1 Worked Solutions 1 2 3 4 5 6 7 8 9 10 C B D A B C A B B B 11 12 13 14 15 16 17 18 19 20 D B C D B A D C C C 21 22 23 24 25 26 27 28 29 30 C B C D D B D B C D 31 32 33 34 35 36 37 38 39 40 C A A B B B B A D D 1 The mass percentage of magnesium in a mixture of magnesium chloride (Mr = 95.3) and magnesium nitrate (Mr = 148.3) was found to be 21.25%. What mass of magnesium chloride is present in 323 g of the mixture? A 151 g B 165 g C 172 g D 181 g (24.3/95.3)(x) + (24.3/148.3)(1 – x) = 0.2125 Solving for x, x = 0.5338 Mass of magnesium chloride = 0.5338 x 323 = 172g 2 Which conversion results in a loss of electrons for the underlined species? A NO3 − to NO2 (+5 to +4) B NO2 − to NO3 − (+3 to +5) A loss of electrons results in an increase in oxidation state. C S2O8 2− to SO4 2− (+7 to +6) D S4O6 2− to S2O3 2− (+2.5 to +2)

2 [Turn Over 3 Which of the following pairs shows Gas Y deviating more from ideal gas behaviour than Gas X at the same temperature and pressure? Gas X Gas Y A HF HCl The pd-pd interactions between HCl molecules are weaker than the hydrogen bonds between HF molecules, so HCl possesses less significant IMF and is more ideal. B H2O H2 The id-id interactions between H 2 molecules are weaker than the hydrogen bonds between H2O molecules, so H2 possesses less significant IMF and is more ideal. C I2 Br2 The id -id interactions between Br 2 molecules are weaker than t he id -id interactions between I 2 molecules, as Br 2 has a smaller electron cloud , so Br2 possesses less significant IMF and is more ideal. D O2 NO2 The pd-pd interactions between NO2 molecules are stronger than the id-id interactions between O2 molecules, so NO2 possesses more significant IMF and is less ideal. 4 Use of the Data Booklet is relevant to this question. Which of the following shows the correct increasing trend for the angle of deflection when placed in an electric field? A Cl − < Ru3+ < Zn2+ B Ru3+ < Cl − < Zn2+ C Cl − < Zn2+ < Ru3+ D Zn2+ < Ru3+ < Cl − Angle of deflection 𝛼 𝑐ℎ𝑎𝑟𝑔𝑒 𝑚𝑎𝑠𝑠 Cl − < Ru3+ < Zn2+ 1/35.5 < 3/101 < 2/65.4 0.0282 < 0.0297 < 0.0306

3 [Turn Over 5 Which of the following cannot form dimers? A CH3COOH dimerization via hydrogen bonds B CH3CHO Incapable of forming intermolecular hydrogen bonding between CH3CHO molecules C AlCl3 dimerization via dative bonds D NO2 dimerization via formation of covalent bond

4 [Turn Over 6 Which of the following species is planar and does not have dative bonding? A PO4 3− tetrahedral (non-planar), no dative bonds B SO4 2− tetrahedral (non-planar), no dative bonds C CO3 2− trigonal planar (planar), no dative bonds D NO3 − trigonal planar (planar), 1 dative bond

5 [Turn Ove