A-LEVEL PAPER 1 PP9 MS

1    (a)    MgCl2(s) → Mg2+(g) + 2Cl−(g)
1
(b)     The magnesium ion is smaller / has a smaller radius / greater charge density (than the calcium ion)
If not ionic or if molecules / IMF / metallic / covalent / bond pair / electronegativity mentioned, CE = 0
1
Attraction between ions / to the chloride ion stronger
Allow ionic bonds stronger
Do not allow any reference to polarisation or covalent character
Mark independently
1
(c)     The oxide ion has a greater charge / charge density than the chloride ion
If not ionic or if molecules / IMF / metallic / covalent / bond pair mentioned, CE = 0
Allow oxide ion smaller than chloride ion
1
So it attracts the magnesium ion more strongly
Allow ionic bonds stronger
Mark independently
1
(d)     ΔHsolution = ΔHL + ΣΔHhyd Mg2+ ions + ΣΔHhyd Cl− ions
Allow correct cycle
1
−155 = 2493 + ΔHhyd Mg2+ ions − 2 × 364
ΔHhyd Mg2+ ions = −155 − 2493 + 728
1
= −1920 (kJ mol−1)
Ignore units
Allow max 1 for +1920
Answer of + or −1610, CE = 0
Answer of −2284, CE = 0
1
(e)     Water is polar / O on water has a delta negative charge
Allow O (not water) has lone pairs (can score on diagram)
1
Mg2+ ion / +ve ion / + charge attracts (negative) O on a water molecule
Allow Mg2+ attracts lone pair(s)
M2 must be stated in words (QoL)
Ignore mention of co-ordinate bonds
CE = 0 if O2− or water ionic or H bonding
1
(f)     Magnesium oxide reacts with water / forms Mg(OH)2
Allow MgO does not dissolve in water / sparingly soluble / insoluble
1
[11]

2.	(a)     ∆G = ∆H - T∆S
Ignore ө
1

(b)     0.098            or                 98
Allow 0.097 to 0.099/97 to 99
Allow 0.1 only if 0.098 shown in working
1
kJ K–1 mol–1                      J K–1 mol–1
Allow in any order
Unless slope is approx. 100(90-110) accept only kJ K–1 mol–1. If no slope value given, allow either units
1
–∆S/∆S
1
(c)     ∆G becomes negative
Mark independently unless ∆G +ve then CE = 0
1
So reaction becomes spontaneous/feasible
Or reaction can occur below this temperature
Or reaction is not feasible above this temperature
1
(d)     Ammonia liquefies (so entropy data wrong/different)
Allow any mention of change in state or implied change in state even if incorrect
eg freezing/boiling
1
[7]
 
3.    (a)    Proton donor or H+ donor
1
(b)     (i)      
 
If Ka wrong, can only score M1 below.
Must be ethanoic acid not HA
Must have square brackets (penalise here only) but mark on in (b)(ii).
1
(ii)     M1  [H+] = 10−2.69 OR 2.042 × 10−3 (mol dm−3)
1
M2  
Ignore ( )
Mark for correctly rearranged expression incl [H+]2
1
M3

If M2 wrong no further marks.
1
M4  = 0.238 (mol dm−3) Allow 0.229 − 0.24
1

(c)    (i)      ClCH2COOH      ClCH2COO− + H+
OR ClCH2COOH + H2O      ClCH2COO− + H3O+
Allow 
Allow ClCH2CO2H and ClCH2CO 2−
1
(ii)     M1  Cl is (more electronegative so) withdraws electrons
       OR negative inductive effect of Cl
Ignore electronegativity.
Ignore chloroethanoic acid has a lower Ka value.
Allow Cl reduces +ve inductive effect of methyl group.
1
M2  Weakens O–H bond
       OR O–H bond is more polar
       OR reduces negative charge on COO−
       OR stabilizes COO− (more)
M1 & M2 are independent marks.
Ignore H+ lost more easily.
1
(d)     (i)      A
1
(ii)     C
1
(iii)    D
1
(e)     M1  Mol NaOH = mol OH− = (19.6 × 10–3) × 0.720 = 1.41(1) × 10−2
Mark for answer.
1
M2  Mol H2SO4 = (26.4 × 10−3) × 0.550 = 1.45(2) × 10−2
Mark for answer.
1
M3  Mol H+ added = 2 × (1.452 × 10−2) = 2.90(4) × 10−2
       OR
       XS mol H2SO4 = 7.46(4) × 10−3
If factor × 2 missed completely (pH = 2.05)
or used wrongly later,
can score max 4 for M1, M2, M5 & M6
1
M4  XS mol H+ = 0.0149(3)
1
M5  For dividing by volume
       [H+ ] = 0.0149(3) × (1000 / 46.0) = 0.324 − 0.325 mol dm−3
If no use or wrong use of volume lose M5 and M6
ie can score 4 for pH = 1.83 (no use of vol)
Treat missing 1000 as AE (−1) & score 5 for pH = 3.49
1
M6  pH = 0.49
2dp (penalise more or less).
If × 2 missed & vol not used, pH = 3.39 scores M1 & M2 only.
1
[18]

4.    (a)     Z
Mark independently.
1
The idea that the solution contains both HA and A−
1

(b)     pH
1
[HA] = [A−]
Accept solution half neutralised.
1
pH = pKa
Accept [H+] = Ka
1
[5]

5.    (a)    It has mobile ions / ions can move through it / free ions
Do not allow movement of electrons.
Allow specific ions provided they are moving but do not react.
1
(b)     Chloride ions react with copper ions / Cu2+ OR [CuCl4]2− formed
If incorrect chemistry, mark = 0
1
(c)     The Cu2+ ions / CuSO4 in the left-hand electrode more concentrated
Allow converse.
1
So the reaction of Cu2+ with 2e− will occur (in preference at) left-hand electrode / Cu → Cu2+ + electrons at right-hand electrode
Allow left-hand electrode positive / right-hand electrode negative.
Also reduction at left-hand electrode / oxidation at right-hand electrode.
Also left-hand electrode has oxidising agent / right-hand electrode has reducing agent.
Allow E left-hand side > E right-hand side
1
(d)     (Eventually) the copper ions / CuSO4 in each electrode will be at the same concentration
1
(e)     (i)      −3.05 (V)
Must have minus sign.
−3.05 only.
1
(ii)     LiMnO2 → Li + MnO2 correct equation
Allow 1 for reverse equation.
Allow multiples.
1
Correct direction
If Li+ not cancelled but otherwise correct, max = 1
If electrons not cancelled, CE = 0
LiMnO2 → Li + MnO2 scores 2
Li+ + LiMnO2 → Li++ Li + MnO2 scores 1
Li + MnO2 → LiMnO2 scores 1
1
(iii)    Electricity for recharging the cell may come from power stations burning (fossil) fuel
Allow any reference to burning (of carbon-containing) fuels.
Note combustion = burning.
1
[9]

6.   (a)     Platinum electrode
1
Solution in beaker is a mixture of named soluble iron(II) compound and named soluble iron(III) compound
Allow correct formulae for the iron compounds.
1
Concentrations of Fe(II) and Fe(III) ions are both 1 mol dm−3
Ignore any references to temperature.
If eg Fe2(SO4)3 used then concentration must be 0.5
1
(b)     Purpose: Allow movement of ions between electrodes
Allow to maintain an electric circuit.
Do not allow reference to movement of electrons in salt bridge.
1
Requirement: Must not react with the electrolyte / ions in solution
Do not allow ‘must not react’ without further qualification.
1
[5]

7.      (a)     (i)      Two (1) lone pair donor / electron pair donor (1) atoms
Allow:– forms two co-ordinate bonds (1)
NOT atom with two lone pairs
(ii)     

Correct ligand structure (1) 
penalise any error
Six correct O–Fe bonds (1)
Correct charge (1)
N.B. Penalise the second mark if arrow from Fe shown
N.B. Ignore charges on atoms
5
(b)     (Substitution of a monodentate ligand by a) bi or multidentate
ligand (1) giving a more stable complex (1) or with an increase
in entropy / disorder or forming a ring / cage complex / structure
(crab like)
2
(c)     (i)      [AgCl2]– or AgCl2– (1)
(ii)     Chloride or Cl– big or large or repel (1)
NOT Cl2 or Cl+ or Cl
Allow ‘chlorine ion’
2

(d)     (i)      (Both) ions are negative or ions repel or High Ea (1)
(ii)     Meaning of the term autocatalytic: A product of the reaction acts
as a catalyst (1)
NOT a self catalysing reaction (0)
Catalyst: Mn2+ or Mn3+ (1)
(iii)     Mn2+ converted into Mnn+ or Mn2+ oxidised (1)
Mnn+/oxidised species then oxidises/reacts with C2O42– (1)
5
[14]
 
8.     (a)     Iron
1
Heterogeneous; catalyst in a different phase from
that of the reactants
1
          Poison; a sulphur compound (allow sulphur)
1
Poison strongly adsorbed onto active sites/ blocked
1
Poison not desorbed or reactants not adsorbed or
catalyst surface area reduced
1
(b)     Pale green solution                                                                                          1
Green precipitate formed
1
Insoluble in excess ammonia
1
Equation:
 Species
1
Balance
1
NB     Allow equations with H2O and OH – if reaction of H2O with NH3 also given
Max 4
[9]
 
9.   (a)     Stop the formation of MnO2 / Ensures all MnO4– reacts to form Mn2+ / becomes colourless
1
(b)     Weak acid / Does not supply sufficient H+
1
(c)     It is self-indicating / Purple to colourless end-point or vice versa
If colours mentioned they must be correct.
1
[3]

10.        (a)     As a droplet from the funnel could enter the burette / affect volume / readings / titre
1
(b)     Air bubble in jet or wtte
Do not allow misreading burette or overshooting end point.
1
(c)     Ensures all reagents are able to react / mix / come into contact
Accept no reagent is left unreacted on sides of flask
Do not allow any reference to ‘removal’ of the solution unless it is clear that it is added to the flask.
1

(d)     The added water does not affect the mols / amount of reagents / reactants / solution Z
Do not allow mols of solution or mols in the flask.
Allow water does not react with the reagents / water is not one of the reactants
Do not allow ‘water is not involved’
1
[4]

11.        (a)     (Biocide) reacts with bacteria / used up killing bacteria
Max two marks
Chlorine given off / evaporates
Do not allow “chlorine has reacted with water” alone.
Chlorine has reacted with water to form (HCl and) O2
Do not allow products of HCl and HOCl alone
2
(b)     the concentration of the remaining solution (after a sample has been removed) is unchanged.
1
(c)     So that all chlorine was reacted / reduced
Do not allow ‘all of the iodide was oxidised’
1
(d)     The Eo value for the iodine half-equation is more positive than that for the thiosulfate
Allow = 0.45
Must refer to values
1
(e)     S2O32− + I2  I− + S4O62−
Allow multiples
1
[6]

12.	(a)	
	
	(b)

(c)		
	(d)		
		
	(e)		
		
	(f)		
	(g)		
	(h)	
[14]