2811_Jan_02MS

2811_Jan_02MS - OCR Advanced Subsidiary GCE in Chemistry...

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Unformatted text preview: OCR Advanced Subsidiary GCE in Chemistry 2811 January 2002 Chemistry Foundation Subject: Chemistry Foundation Code: 2811 Session: January Year: 2002 Final Mark Scheme RR 12th JANUARY 2002 MAXIMUM MARK 2811 Final MS Jan2002.doc Page 1 of 10 90 2811 January 2002 07/02/2002 OCR Advanced Subsidiary GCE in Chemistry 2811 January 2002 Chemistry Foundation 1. (a) Mark vertically or horizontally. species number of protons electrons 20 18 17 18 Ca2+ − Cl [2] 2 2 6 2 (b) 1s 2s 2p 3s 3p 6 0 4s is OK [1] (c) (i) CaCl2 [1] (ii) Ca 2+ ion shown correctly − ; 2 Cl ions shown correctly For Ca2+, either 8 electrons or no electrons For Cl−, dot and crosses required. [2] (iii) ionic bonds/ionic bonding/electrostatic or ionic attraction/forces [1] (d) (i) pH becomes (more) alkaline/increases Ca(OH)2 forms/hydroxide ions form/H+ is removed by electrolysis (2nd mark depends on 1st: it ‘explains’ why the solution becomes alkaline) [2] (ii) ‘charge carriers’ move in aqueous and do not move in solid charge carriers are ions 1st point identifies that something that is charged (electrons/ions/charge carriers) can move and not move when solid. 2nd point identifies what the carriers are. ‘Ions move’ in isolation scores 1 mark [2] (e) (i) Cl2: 0 HClO +1 or 1 or 1+ HCl −1 or 1− [3] −3 (ii) 0.003 / 3 x 10 mol [1] (iii) purification/sterilisation/disinfect/killing bacteria ow but....not ‘bleach’/ not ‘cleaning’/ not ‘swimming pools’ [1] [Total: 16] 2811 Final MS Jan2002.doc Page 4 of 10 2811 January 2002 07/02/2002 OCR Advanced Subsidiary GCE in Chemistry 2811 January 2002 Chemistry Foundation 2. (a) Energy change when each atom in 1 mole loses an electron of gaseous atoms (to form 1 mole of gaseous 1+ ions). [3] (b) (i) Electrons added to same shell /same or similar shielding increasing nuclear charge/number of protons electrons experience greater attraction or pull / atomic radius decreases [3] (ii) Al has an electron in the p sub-shell/ has a p electron /different sub-shell/different . type of orbital (not a different shell or a different orbital) If Al not stated then assume that response applies to it! Al sub-shell at higher energy (than s) [2] (c) electron is further from nucleus/ electron in a different shell electron experiences more shielding (not sub-shell or orbital) (more is essential here) nuclear attraction decreases /distance or shielding outweighs nuclear attraction / effective nuclear charge decreases [3] (d) First ionisation energy of Ne = 1600 kJ mol−1/ > 1600 kJ mol−1 [1] (e) Al2+(g) → Al3+(g) + e− equation ; state symbols correct [2] [Total: 14] 2811 Final MS Jan2002.doc Page 5 of 10 2811 January 2002 07/02/2002 OCR Advanced Subsidiary GCE in Chemistry 2811 January 2002 Chemistry Foundation 3. (a) (i) oxidation loss of electrons/ increase in oxidation number/gain of O/loss of H reduction gain of electrons/ decrease in oxidation number/loss of O/gain of H [2] (ii) 2Mg(s) + O2(g) → 2MgO(s) / Mg(s) + ½ O2(g) → MgO(s) equation ; state symbols correct [2] (iii) oxidation reduction Mg → Mg 2+ − + 2e O2 + 4e− → 2O2− / ½O2 + 2e− → O2− Ignore state symbols [2] (b) (i) Solid no longer dissolves/ disappears/solid remains Ignore references to changes of pH/use of indicators [1] (ii) 25.0 x 2.00/1000 = 0.0500 mol [1] (iii) 0.0250 mol MgO (i.e. answer to (ii)/2) [1] (iv) M(MgO) = 24.3 + 16 = 40.3 0.0250 x 40.3 = 1.0075 g = 1.01 g (i.e. answer to (iii) x answer to M(MgO)) (i.e. 1 mark for sig figs. 10.1 g would automatically score both the marks here.) If a candidate uses 24 for Mg, answer to 3 sig figs is 1.00 g. [3] (v) Not a redox reaction because no species changes oxidation number evidence of working using actual oxidation numbers of at least one species (2nd point could well in the equation in part (b). Indicate this with an arrow to show this evidence) [2] (c) strong forces to be broken/high amount of energy required to break lattice /giant structure forces between ions/ionic bonding [2] [Total: 16] 2811 Final MS Jan2002.doc Page 6 of 10 2811 January 2002 07/02/2002 OCR Advanced Subsidiary GCE in Chemistry 2811 January 2002 Chemistry Foundation 4. (a) attraction of an atom/element for electrons in a covalent bond/bonded pair/molecule [2] (b) δ+ H−Nδ− δ− F−Bδ+ all 3 correct δ+ H−Iδ− ; 2 correct scores 1 mark [2] (c) dot-and-cross diagram for NH3 dot-and-cross diagram for BF3 NH3 BF3 [2] (d) F N H H B H F F bond angle: 107 ± 1° bond angle: 120° shape: pyramidal shape: trigonal planar/planar triangle [4] (e) NH3 has a non-symmetrical shape/ BF3 is symmetrical in NH3 dipoles do not cancel or there is an uneven charge distribution / in BF3 dipoles cancel or there is an even charge distribution [2] (f) H bond shown from N of one NH3 molecule to H of another NH3 molecule [1] (g) (i) NH3 has a lone pair/ NH4+ has no lone pair/ NH4+ has a dative (covalent) or coordinate bond bonded pair repels less/ lone pair repels more not repelling atoms [2] (ii) Add silver nitrate (solution)/ silver ions yellow precipitate or Add chlorine/bromine violet in added organic solvent or blue-black colour with added starch [2] [Total: 17] 2811 Final MS Jan2002.doc Page 7 of 10 2811 January 2002 07/02/2002 OCR Advanced Subsidiary GCE in Chemistry 2811 January 2002 Chemistry Foundation 5. (a) CaCO3 heat CaO + solid A CO2 gas B excess water Ca(OH)2 HCl(aq) solution C CaCl2 + solution D H2O liquid E CO2(g) milky suspension of CaCO3 in water excess CO2(g) Ca(HCO3)2 solution F alternative answers as names: A calcium oxide/qulicklime; B carbon dioxide; C calcium hydroxide/lime water; D calcium chloride; E water; F calcium hydrogencarbonate/ calcium bicarbonate [6] (b) Molar mass of CaCO3 = 100.1 or 100 4 x 100.1 or 100 g CaCO3 = 400.4 or 400 ∴ 25 x 400.4 or 400/446.6 kg CaCO3 = 22.41 or 22.39 kg Accept 22 kg or 22.4 kg [3] (c) (i) Ca(OH)2 + CO2 → CaCO3 + H2O ignore state symbols [1] (ii) CaCO3 reacts with acids [1] [Total: 11] 2811 Final MS Jan2002.doc Page 8 of 10 2811 January 2002 07/02/2002 OCR Advanced Subsidiary GCE in Chemistry 2811 January 2002 Chemistry Foundation 6. In this question, 1 mark is available for the quality of written communication. (a) observations: 2 marks chlorine: Cl2 + bromide → orange/brown/yellow/red in organic solvent bromine: Br2 + iodide → orange/brown/yellow/purple with organic solvent equations: 2 marks chlorine: Cl2 + 2Br− → Br2 + 2Cl− / Cl2 + 2I− → I2 + 2Cl− bromine: Br2 + 2I− → I2 + 2Br− 2 ‘correct’ unbalanced equations scores 1 mark reactivity: 1 mark Therefore reactivity decreases down group/ Cl2 > Br2 > I2 / / Cl2 displaces bromine and iodine AND bromine displaces iodine (this could be shown in a table) [sub-total: 5] (b) how atom changes: 2 marks as group descends, more shells are added/ increasing radius of atom and increased electron shielding result: 1 mark down the group,....... electron to be captured experiences less attraction /less effective nuclear charge to capture an electron /electrons gained less easily It must be clear that an electron is gained through this process to score the mark [sub-total: 3] 8 marking points → [7 max] Q – legible text with accurate spelling, punctuation and grammar [1] [Total: 8] 2811 Final MS Jan2002.doc Page 9 of 10 2811 January 2002 07/02/2002 OCR Advanced Subsidiary GCE in Chemistry 2811 January 2002 Chemistry Foundation 7. In this question, 1 mark is available for the quality of written communication. (a) calculate from weighted mean: 79 x 55.0/100 + 81 x 45.0/100 Ar = 79.9 [sub-total: 2] (b) ionisation by electron beam/bombardment/gun acceleration/shot along/moved deflection by magnetic field/with a magnet deflection depends on mass/lighter particles deflected more particles travelling are ions relative heights or peak areas gives the abundance 6 marking points → [5 max] [sub-total: 5] Clear, well-organised, using specialist terms required use of all these words: ionisation, acceleration, deflection, detection [1] [Total: 8] 2811 Final MS Jan2002.doc Page 10 of 10 2811 January 2002 07/02/2002 ...
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