Download mark scheme - A-Level Chemistry

Paddington Academy
AS-LEVEL PAPER 1 PP1 MS
1.
(a)
Proton: mass 1, charge + 1 (1)
Neutron: mass 1, charge 0 (1)
Electron mass 1/1840, charge -1 (1)
Allow mass = 0, or negligible, or 1/1800 to 1/2000
Isotopes have the same number of protons (1)
OR atomic number
different number of neutrons (1)
Isotopes have the same electronic configuration (1)
OR same number of electrons
Chemical properties depend on electrons (1)
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(b)
×12 (1)
OR
× 12 or in words
Spectrum gives (relative) abundance (1)
OR % or amount
And m/z (1)
Multiply m/z by relative abundance for each isotope (1)
Allow instead of m/z mass no, Ar or actual value from
example
Sum these values (1)
Divide by the sum of the relative abundances (1)
only award this mark if previous 2 given
Max 2 if e.g. has only 2 isotopes
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[14]
2.
(a)
(i)
0.00301/ 3.01 × 10–3;
Penalise < 3sf in (a)(i);
Allow 3.01 × 10–3 – 3.05 × 10–3.
(for candidates who have used Mg as 24)
(ii)
0.00602
Allow correct answer a(i) × 2.
(iii)
0.00965/ 9.65 × 10–3;
Allow 0.009646/ 0.0096-0.0097.
(iv)
0.00363 moles;
Allow range 0.0035 to 0.0037.
Allow (a)(iii) – 2 (a)(ii) (must be positive).
1
1
1
1
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(b)
PV = nRT;
Allow all capitals/ lower case.
1
V=
;
M2 Mark is for all numbers correct.
If units in answer are in dm3 allow this expression with 96 in
denominator.
1
0.0132 m3/ 13.2 dm3;
M3 Must have correct units/
allow 13200 cm3.
Allow min 2 sig figs in answer.
1
(c)
O = 69.6 (%);
1
2.17 : 4.35
Use of 7/8 CE then M1 only.
1
(1 : 2) NO2
Mark for formula not ratio.
If NO2 and no working shown then allow 1 mark.
If 69.6% + NO2 only = 2.
Need to see evidence of M2 working.
Allow M2 conseq on the wrong M1 (ie max 1).
1
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3.
(a)
Iodine – molecular
Not covalent lattice
1
Graphite – macromolecular/giant covalent/giant atomic
1
(b)
Layers of (C atoms)
1
Connected by covalent bonds within each layer
1
Van der Waals forces/IMF between layers/weak forces
between layers
1
Many/strong covalent bonds need to be broken
If any other element mentioned other than C, CE = 0
Ignore the no of covalent bonds around the C if mentioned
The first 3 marks could be scored with a labelled diagram.
Need to label or state covalent bonds within the layers.
Covalent or ionic or metallic bonds between molecules CE =
0
1
(c)
Van der Waals forces are weak or easily broken
Not vdw between atoms
1
Van der Waals between molecules (or implied)
Allow weak IMF = 2
1
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(d)
Does not have delocalised/free electrons
Only allow answer with respect to iodine
Not all electrons used in bonding
Ignore free ions
1
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4.
(a)
They are elements (1)
Ignore irrelevant comments
(b)
Enthalpy change (1)
or heat energy change or heat change or ΔH or any named
enthalpy change C.E. if change not mentioned
Independent of route (1)
OR depends on initial and final states
Only give second mark if first mark awarded except allow if
energy used instead of enthalpy
1
2
(c)
ΔH = ΣΔHf (products) ‑ ΣΔHf (reactants) (1) (Or a cycle)
= 2 × –242 + ½ × –394 – (–365) (1) (also implies first mark)
= -316 kJ mol–1 (1)
3
Ignore no units penalise wrong units
+316 scores 1/3
[6]
5.
(a)
(i)
E + 3F → 2C + D
(ii)
mol-1dm3
(iii)
(forward reaction is) exothermic or more products formed
(i)
Moles of iodine = 0.023
1
1
1
(b)
1
Moles of HI = 0.172
1
(ii)
Kc =
(iii)
V cancels in Kc expression
1
1
(iv)
Kc =
1
= 0.0179 or 1.79 × 10–2
1
(v)
Kc = 55.9 or 56
Conseq i.e. (answer to (iv))–1
1
[10]
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6.
(a)
Compound 1
If M1 incorrect, CE = 0
M1
1
No visible change with H2SO4
M2
1
Gives white ppt with NaOH
M3
1
(b)
BaCO3
1
The carbonate ion releases CO2
1
but the BaSO4 formed is highly insoluble.
1
(c)
Compound 4
1
Sr(OH)2 + H2SO4
SrSO4 + 2H2O
Allow ionic equation; ignore state symbols
1
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7.
(a)
M1 Cl2 + 2Br−
2Cl− + Br2
Accept a correct equation using ½ Cl2 but no other multiples
M2 solution goes orange / yellow ( from colourless)
Ignore reference to brown colour
Penalise incorrect observations eg fumes, precipitates
2
(b)
M1 Cl2 + 2NaOH
NaClO + NaCl + H2O
(NaOCl)
Or a correct ionic equation
Ignore reference to “swimming pools” and to “disinfectant”
M2 bleach or kills bacteria / bacteriacide / micro-organisms / microbes
M3 sodium chlorate(I) ONLY
(c)
M Cl2 + H2O
HClO + HCl
(HOCl)
Equilibrium symbol required in M1
Accept ionic RHS
M2
The (health) benefit outweighs the risk or wtte
OR
a clear statement that once it has done its job, little of it remains
OR
used in (very) dilute concentrations / small amounts / low doses
3
2
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(d)
M1 Silver nitrate OR AgNO3 (with or without nitric acid)
For M1
If only the formula is written then it must be correct
If both the formula and the name are written then ignore
incorrect attempt at the formula, but penalise an incorrect
name
M2 (depends on M1)
white precipitate / white solid
If the reagent is incomplete eg Ag+ ions, penalise M1 and
mark on
M3 Ag+ + Cl−
AgCl
Penalise both M1 and M2 for alkaline AgNO3 OR for the use
of HCl to acidify the silver nitrate OR for Tollens’ reagent
3
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8.
D
9.
D
10.
C
11.
D
12.
B
13.
B
14.
D
15.
B
16.
C
[1]
[1]
[1]
[1]
[1]
[1]
[1]
[1]
[1]
17.
B
[1]
18.
D
[1]
19.
B
20.
D
[1]
[1]
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