AS-LEVEL PAPER 1 PP2 MS

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3.		
	
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4.	(a)    Enthalpy change when 1 mol of an (ionic) compound/lattice (under standard 
conditions)
Allow heat energy change
1
Is dissociated/broken/separated into its (component) ions
1
The ions being in the gaseous state (at infinite separation)
Mark independently. Ignore any conditions.
1
(b)     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
1

(c)     Mg2+(g) + O(g) + 2e–
Ignore lack of state symbols
Penalise incorrect state symbols
1
Mg2+(g) + O–(g) + e–
1
Mg2+(g) + O2–(g)
1
First new level for Mg2+ 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
1
Next level for Mg2+ and O– below that
Next level for Mg2+ and O2– above that and also above that for Mg2+ and O
Allow +124
Allow M4 with incorrect number of electrons
(d)     LE MgO = 602 + 150 + 736 + 1450 + 248 – 142 + 844
Note use of 124 instead of 248 CE=0
1
= +3888 kJ mol–1
Allow 1 for –3888
Allow no units
Penalise wrong units
1
(e)     Forms a protective layer/barrier of MgO / MgO prevents oxygen attacking Mg
Allow activation energy is (very) high
Allow reaction (very) slow
1
(f)     ∆G = ∆H – T∆S
∆S = (∆H − ∆G)                T
1
∆S = (–602 – (–570)) × 1000/ 298
1
= –107 J K–1 mol–1 / –0.107 kJ K–1 mol–1
If units not correct or missing, lose mark
Allow –107 to –108
+107 with correct units scores max 1/3
1
(g)     1 mol of solid and 0.5 mol of gas reactants form 1 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
1
System becomes more ordered
Allow consequential provided ∆S is –ve in 1(f)
If ∆S is +ve in 1(f) can only score M1
1
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5.     (a)     (i)      Ka =  (1)
(ii)     (1)     Ka =  (1)
(2)     [H+] =  = 1.96 × 10–3 (1)
(3)     pH = -log10[H+] (1)
can score independently
(4)     pH = 2.71 (1)
2 d.p. essential
If forget √ can score (1) and (3) for pH = 5.42
5
(b)     (i)      moles acid =  (1) = 5.50 ×10–3
= 
 x = 25 ×  or 5.50 × 10–3 × 
       = 36.7 (or 37) cm3 (or 36.6) (1)
          
NOT 36 NOR 37.0 units must match
(ii)     Indicator:                  thymol blue (1)
Explanation:             weak acid – strong base (1)
                                 equivalent at pH > 7 (1)
                                 or high pH
5
(c)     (1)     mol NaOH added =  = 0.050 (1)
If wrong Mr: CE  lose marks (1) and (2) then mark on
consequentially → max 4
(2)     mol CH3COOH left = 0.220 – 0.050 = 0.170 (1)
(3)     mol CH3COO– formed = 0.050 (1)
(4)     [H+] = Ka  OR pH = pKa +  etc (1)
If expression wrong no marks for 4 / 5 / 6
can score (1) to (4) in (5)
(5)     [H+] = 1.74 × 10–5 ×  OR pH = 4.76 + log (1)
(6)     pH = 4.23 (1)
Correct answer gets (1)(1)(1)(1)(1)(1)
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 (1) (3) (4) (6) = max 4
for pH = 4.12 if upside down; answer 5.29 scores 3 for (1) (2) (3)
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6.     (a)     (i)      HgO
1
(ii)     Hg2+ + 2e– → Hg
1
(iii)     2H2O + SO2 → H2SO4 + 2e– etc
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(iv)    Cl2 + 2e– → 2Cl–
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(b)     (i)      Vanadium species: VO2+
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         Oxidation state: 5
1
         Half-equation: V2+ + 2H2O → VO2+ + 4H+ + 3e–
1
(ii)     Cell e.m.f 0.60 V
1
         Change in e.m.f , Increases
1
More Fe3+ ions to accept electrons
1
Fe3+/Fe2+ electrode becomes more positive
1
(c)     (i)      2H2 → 4H+ + 4e–
1
         4e– + O2 + 2H2O → 4OH–
1
         Overall equation 2H2 + O2 → 2H2O

(ii)     Unchanged
1
(d)     Economic disadvantage; Use of CH4 or cost of producing or high temp
1
          Environmental disadvantage; Makes CO2
1
(e)     Cost of manufacture of solar cells
1
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7.      (a)     Incomplete (or partially filled) d orbitals/sub-shells
Do not allow d shell
1
(b)     Variable oxidation states
1
(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)
1
(ii)     Cis platin drawn out as square planar
Allow NiX42– etc
1
(iii)     [CuCl4]2– drawn out as tetrahedral ion
Or [CoCl4]2– drawn out
1

(d)     (i)      SO2 + 1/2O2 → SO3
Allow multiples
Allow SO2 + 1/2O2 + H2O → H2SO4
ignore state symbols
1
(ii)     In a different phase/state (from the reactants)
1
(iii)     V2O5 + SO2 → V2O4 + SO3
can be in either order
1
V2O4 + 1/2O2 → V2O5
allow multiples
1
(iv)    Surface area is increased
1
By use of powder or granules or finely divided
Allow suspending/spreading out onto a mesh or support
1
(e)     (i)      Forms two or more co-ordinate bonds
Allow more than one co-ordinate bond or donates more than 1 electron pair.
Do not allow “has more than one electron pair”
Allow uses more than one atom to bond (to TM)
1
(ii)     Number of product particles > Number of reactant particles
Allow molecules/entities instead of particles
Penalise incorrect numbers (should be 2→5)
1
Disorder increases or entropy increases
(or entropy change is positive)
Allow ΔG must be negative because ΔH = 0 and ΔS is +ve
1
(iii)     6
1
Cyanide strongly bound to Co (by co-ordinate/covalent bond)
1
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8.      (a)     Electron transitions/electrons excitedin d shell (1) or d-d transition
Do NOT allow charge transfer
          (Energy in) visible range (1)
(NOT emits in visible region)
2
(b)     Change 1: (Different) oxidation states (1)
Change 2 : (Different) ligands (1)
Change 3: (Different) co-ordination number (1)
Do not allow shape as an answer
3

(c)     Add an appropriate (or a given correct) ligand to intensify colour (1)
e.g. thiocyanate (CNS)— or bipyridyl
Make up solutions of known concentration (1)
Measure absorption or transmission (1)
Plot graph of results or calibration curve (1)
Measure absorption of unknown and (1)
compare
N.B.:  Allow concentration statement if included in graph statement
          Allow adsorption but circle the d
          Also

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