CHEMISTRY
HCI_H2_CHEM_C2_P3_MS.pdf

HCI_H2_CHEM_C2_P3_MS.pdf - 2 2017 C2 Prelims Paper 3 Mark...

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2 © Hwa Chong Institution 2017 9729 / 03 / C2 Prelim 2017 2017 C2 Prelims Paper 3 Mark Scheme 1 (a) No. of moles of NaOH = 0.100 x 26.50/1000 = 2.65 x 10 -3 mol No. of moles of H 2 SO 4 (in 25cm 3 ) = ½ x 2.65 x 10 -3 = 1.325 x 10 -3 mol [1/2] No. of moles of H 2 SO 4 (in 250cm 3 ) = 1.35 x 10 -3 x 250/25.0 [1/2] = 0.01325 mol No. of moles of H 2 SO 4 reacted = (0.425 x 100/1000) 0.01325 [1/2] = 0.02925 mol No. of moles of Cu 3 (CO 3 ) 2 (OH) 2 = 0.02925 x 1/3 [1/2] = 9.75 x 10 -3 mol Mass of azurite = 9.75 x 10 -3 x 344.5 [1/2] = 3.359 g % by mass of pure azurite in the powdered rock = 3.359/3.70 x 100% = 90.8% [1/2] (b) (i) x = 2 [1] [Cu(NH 3 ) 2 ] + [1] (ii) [O] [Cu(NH 3 ) 2 ] + + 2NH 3 [Cu(NH 3 ) 4 ] 2+ + e - [R] O 2 + 2H 2 O + 4e - 4OH - Overall: 4[Cu(NH 3 ) 2 ] + + O 2 + 8NH 3 + 2H 2 O 4[Cu(NH 3 ) 4 ] 2+ + 4OH - 2 half-equations: [1/2 each] Overall equation: [1] (c) (i) I 2 (s) + 3C l 2 (g) 2 I C l 3 (s) +38 2(+60) 3(244) I 2 (g) 2 I C l 3 (g) +151 6BE ( I C l ) 2 I (g) + 6C l (g) -162 = +38 + 151 + 3(244) 6BE( I C l ) 120 BE( I C l ) = +160.5 kJmol 1 energy cycle: [2] application of Hess’s Law: [1] correct stoichiometry coefficients: [1]
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