2023 SOTA Yr 6 Chem HL Prelim Exam MS1_2

Mark scheme 2023 HL Prelim P1 P2 Question 1 2 3 4 5 6 7 8 9 10 Answer D C D A B D B B B A Question 11 12 13 14 15 16 17 18 19 20 Answer A A D B A D D B C D Question 21 22 23 24 25 26 27 28 29 30 Answer B C D C C D D C B D Question 31 32 33 34 35 36 37 38 39 40 Answer A C C A C B B A C C Qn Mark scheme Remark 1a chromium: n(Cr) = !".$%&'.(( % *+,!" = 1.32 mol OR oxygen: n(O) = -..!.!.(( = 1.98 mol ✔ ratio n(Cr) : n(O) = 1.32 : 1.98 = 1 : 1.5 = 2 : 3 empirical formula: Cr2O3 ✔

Let the molecular formula be Cr2xO3x. 156 = 2(52.00)x + 3(16.00)x x = 1 molecular formula: Cr2O3 ✔ Allow ecf for empirical and molecular formula. Award [3] for correct final answer. 1b i «promoted» electrons fall back to lower energy level ✔ Energy difference between levels is different ✔ Accept “Cu, Ca and Cr have different nuclear charge” for M2 1bii energy levels are closer together at high energy / high frequency / short wavelength ✔ 1biIi IE = ΔE = hν = 6.63 × 10–34 J s × 1.64 × 1015 s–1 = 1.09 × 10–18 J ✔ 1ci 1s2 2s2 2p6 3s2 3p6 3d5 4s1 OR 1s2 2s2 2p6 3s2 3p6 4s1 3d5 ✔ Do not accept condensed electron configuration like [Ar] 3d5 4s1 1cii Both are paramagnetic. ✔ «both» contain unpaired electrons OR each chromium atom has 6 unpaired electrons and each chromium(III) ion has 3 unpaired electrons. ✔ Accept orbital diagrams showing unpaired electrons.

1ciii H2O is LB as it donates electron pair OR Cr3+ is LA as it accepts electron pair iv Any THREE from: partially filled d-orbitals ligands/water cause d-orbitals to split red light is absorbed as electrons move to a higher energy orbital «in d–d transitions» OR light is absorbed as electrons are promoted «green» colour observed is the complementary colour «of red» 2ai. CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l) ✔ aii. [(-393.50 + (2 x – 285.8 ) – ( -74.0)] ; ✔ -891.1 <<kJmol-1>> ✔ Award 2m for correct final answer; Award 1 m for <<+>> 891.1 kJmol-1 aiii. BE assume all bonds are in gaseous state / H2O formed is in liquid form for literature value/ OWTTE ✔ bi. Methane AND tetrachloromethane is non-polar AND Dichloromethane is polar; ✔ C-Cl bond is polar <<C-H bond is non-polar>>; ✔ In dichloromethane, dipole moment/bond polarities does not cancel out OR In tetrachloromethane, dipole moment/bond polarities cancels out; ✔ bii. London dispersion forces is stronger in tetrachloromethane due to greater number of electrons <<larger molecular mass>> ✔ biii. Methane cannot form hydrogen bond/favourable intermolecular forces of attraction/interaction with water. ✔ ci. (3 x 498) – (4 x O-O in ozone) = <<+>> 285.4; ✔ (O-O in ozone) = << [(3 x 498) - 285.4] / 4 >> = <<+>> 302 <<kJ>> ✔ Award 2m for correct final answer

cii. ; ✔ FC ( -1 +1 0) ✔ ciii. <<Bond energy is greater than O-O single but weaker than O=O double bond>> Both bonds are identical in bond length << due to resonance