AS-LEVEL PAPER 1 PP2 MS

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1 AS-LEVEL PAPER PP2 MS. [8] 2. [8] Page

2 3. [6] 4. (a) Enthalpy change when mol of an (ionic) compound/lattice (under standard conditions) Allow heat energy change (b) Is dissociated/broken/separated into its (component) ions The ions being in the gaseous state (at infinite separation) Mark independently. Ignore any conditions. There is an attractive force between the nucleus of an O atom and an external electron. Allow any statement that implies attraction between the nucleus and an electron Page 2

3 (c) Mg 2+ (g) + O(g) + 2e Ignore lack of state symbols Penalise incorrect state symbols Mg 2+ (g) + O (g) + e Mg 2+ (g) + O 2 (g) First new level for Mg 2+ and O above last on L If levels are not correct allow if steps are in correct order with arrows in the correct direction and correct H values Next level for Mg 2+ and O below that Next level for Mg 2+ and O 2 above that and also above that for Mg 2+ and O Allow +24 Allow M4 with incorrect number of electrons (d) LE MgO = Note use of 24 instead of 248 CE=0 (e) (f) (g) = kj mol Allow for 3888 Allow no units Penalise wrong units Forms a protective layer/barrier of MgO / MgO prevents oxygen attacking Mg Allow activation energy is (very) high Allow reaction (very) slow G = H T S S = ( H G) S = ( 602 ( 570)) 000/ 298 = 07 J K mol / 0.07 kj K mol If units not correct or missing, lose mark Allow 07 to with correct units scores max /3 mol of solid and 0.5 mol of gas reactants form mol solid products Decrease in number of moles (of gas/species) Allow gas converted into solid Numbers of moles/species, if given, must be correct System becomes more ordered Allow consequential provided S is ve in (f) If S is +ve in (f) can only score M T [6] Page 3

4 5. (a) (i) Ka = () (ii) () Ka = () (2) [H + ] = = () (3) ph = -log0[h + ] () can score independently (4) ph = 2.7 () 2 d.p. essential If forget can score () and (3) for ph = (b) (i) moles acid = () = = x = 25 or = 36.7 (or 37) cm 3 (or 36.6) () NOT 36 NOR 37.0 units must match (ii) Indicator: thymol blue () Explanation: weak acid strong base () equivalent at ph > 7 () or high ph 5 (c) () mol NaOH added = = () If wrong Mr: CE lose marks () and (2) then mark on consequentially max 4 (2) mol CH3COOH left = = 0.70 () (3) mol CH3COO formed = () (4) [H + ] = Ka OR ph = pka + etc () If expression wrong no marks for 4 / 5 / 6 can score () to (4) in (5) (5) [H + ] = OR ph = log () (6) ph = 4.23 () Correct answer gets ()()()()()() Mark (5) is for use of correct values of (acid moles) and (salt moles) if one wrong allow ph conseq if both wrong, no further marks e.g. if candidate forgets substitution in (2) he loses (2) and (5) but can score () (3) (4) (6) = max 4 for ph = 4.2 if upside down; answer 5.29 scores 3 for () (2) (3) Page 4 6 [6]

5 6. (a) (i) HgO (ii) Hg e Hg (iii) 2H2O + SO2 H2SO4 + 2e etc (iv) Cl2 + 2e 2Cl (b) (i) Vanadium species: VO2 + Oxidation state: 5 Half-equation: V H2O VO H + + 3e (ii) Cell e.m.f 0.06 V Change in e.m.f, Increases More Fe 3+ ions to accept electrons Fe 3+ /Fe 2+ electrode becomes more positive (c) (i) 2H2 4H + + 4e 4e + O2 + 2H2O 4OH Overall equation 2H2 + O2 2H2O (d) (ii) Unchanged Economic disadvantage; Use of CH4 or cost of producing or high temp (e) Environmental disadvantage; Makes CO2 Cost of manufacture of solar cells [7] 7. (a) Incomplete (or partially filled) d orbitals/sub-shells Do not allow d shell (b) Variable oxidation states (c) (i) [H3N Ag NH3] + Allow [Cl Ag Cl] or similar Cu(I) ion Allow compounds in (i), (ii) and (iii) (eg Cl-Be-Cl) Allow no charge shown, penalise wrong charge(s) (ii) (iii) Cis platin drawn out as square planar Allow NiX4 2 etc [CuCl4] 2 drawn out as tetrahedral ion Or [CoCl4] 2 drawn out Page 5

6 (d) (i) SO2 + /2O2 SO3 Allow multiples Allow SO2 + /2O2 + H2O H2SO4 ignore state symbols (ii) (iii) (iv) In a different phase/state (from the reactants) V2O5 + SO2 V2O4 + SO3 can be in either order V2O4 + /2O2 V2O5 allow multiples Surface area is increased By use of powder or granules or finely divided Allow suspending/spreading out onto a mesh or support (e) (i) Forms two or more co-ordinate bonds Allow more than one co-ordinate bond or donates more than electron pair. Do not allow has more than one electron pair Allow uses more than one atom to bond (to TM) (ii) (iii) 6 Number of product particles > Number of reactant particles Allow molecules/entities instead of particles Penalise incorrect numbers (should be 2 5) Disorder increases or entropy increases (or entropy change is positive) Allow ΔG must be negative because ΔH = 0 and ΔS is +ve Cyanide strongly bound to Co (by co-ordinate/covalent bond) 8. (a) Electron transitions/electrons excitedin d shell () or d-d transition Do NOT allow charge transfer (Energy in) visible range () (NOT emits in visible region) (b) Change : (Different) oxidation states () Change 2 : (Different) ligands () Change 3: (Different) co-ordination number () Do not allow shape as an answer 2 3 [6] Page 6

7 (c) Add an appropriate (or a given correct) ligand to intensify colour () e.g. thiocyanate (CNS) or bipyridyl Make up solutions of known concentration () Measure absorption or transmission () Plot graph of results or calibration curve () Measure absorption of unknown and () compare N.B.: Allow concentration statement if included in graph statement Allow adsorption but circle the d Also 5 [0] 9. Page 7

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Final. Mark Scheme. Chemistry CHEM5. (Specification 2420) Unit 5: Energetics, Redox and Inorganic Chemistry

Final. Mark Scheme. Chemistry CHEM5. (Specification 2420) Unit 5: Energetics, Redox and Inorganic Chemistry Version.2 General Certificate of Education (A-level) January 202 Chemistry CHEM5 (Specification 2420) Unit 5: Energetics, Redox and Inorganic Chemistry Final Mark Scheme Mark schemes are prepared by the