AS-LEVEL PAPER 2 PP3 MS

1.   (a)     Percentage of oxygen is 36.4%
% of oxygen stated or shown in calculation.
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Correct calculation of ratios (C 4.54, H 9.10, O 2.28)
Mark is for correct method, dividing % by Ar
1
Empirical formula C2H4O
Allow consequential answer from wrong percentage of oxygen (max 2 marks).
1
(b)     88
Accept 88.0
Do not penalise correct answer in g.
1
(c)     Ratio MF / EF of 2 (88 / 44.0 = 2)
If use 132 / 44 = 3, molecular formula C6H12O3 scores 2 marks.
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Molecular formula is C4H8O2
Accept consequential answers from (a) and (b)
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[6]

2.     (a)     The enthalpy change when 1 mol of a compound
1
is completely burnt in oxygen
1
under standard conditions, or 298K and 100kPA
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(b)     (i)      C2H6 + 3½O2 → 2CO2 + 3H2O
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(ii)     ΔH = 2 × ΔHfο (CO2) + 3 × ΔHfο (H2O) – ΔHfο (C2H6)
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= – 788 – 858 – (–85)
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= – 1561 kJ mol–1
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(c)     moles methane =  = 6.25 × 10–3
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kJ evolved = 6.25 × 10–3 × 890 = 5.56
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5.56 × 103 joules = (mc)ΔT
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ΔT =  = 46.4 K
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[11]

3.   (a)     Yes, because it is oxidised to ethanal / CH3CHO
OR it is oxidised to a compound that contains CH3CO group
Ignore ‘primary alcohols are oxidised to aldehydes’.
Need ‘yes’ and an explanation to be awarded the mark.
1
(b)     Mr CHI3 = 393.7 (M1)
Allow if clearly shown in a calculation.
Allow 394
1
Moles CHI3 = 10 / 393.7 = 2.54 × 10−2 (M2)
Allow a consequential answer on an incorrect Mr.
2.54 × 10−2 scores M1 and M2.
1
Moles I2 = 7.62 × 10−2 (M3)
Allow 3 × M2.
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Mass I2 = 7.62 × 10−2 × 253.8 = 19.34g (M4)
Allow M3 × 253.8 or M3 × 254
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Scaling 19.34 / 0.832 = 23.2g (M5)
Allow M4 / 0.832
Lose this mark if the answer is not given to 3 significant figures.
Answer without working scores M5 only.
Allow any chemically correct alternative method.
Calculations which combine several steps in one expression can score the marks for all of these individual steps.
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(c)     Remove soluble impurities
Allow ‘remove excess sodium hydroxide / iodine’.
Allow ‘remove excess sodium methanoate / sodium iodide’.
Allow ‘remove excess reagents’.
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(d)     Will not dissolve solid / solid is insoluble in water
Allow ‘will not react with solid’.
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[8]

4.      (a)     (i)      (Free-) radical substitution
Both words needed
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(ii)     UV light/Ultra-violet light/sunlight
OR high temperature/150 °C ≤ T ≤ 500 °C
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(iii)     Propagation (Step)
Ignore “first” or “second”
Accept phonetic spelling
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(iv)    M1    Termination (Step)
M2    2CH3CH2CH2•  C6H14
In M2
C6H14 may be drawn out as CH3CH2CH2CH2CH2CH3
The dot may be anywhere around the terminal CH2 on the radical
Accept C3H7• with dot anywhere
Penalise the absence of any radical dot
2
(v)     C3H8 + 8Br2  C3Br8 + 8HBr
Or multiples
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(b)     (i)      M1    Double bonds are
          electron-rich
OR    electron pair donors
OR    centres of electron density.
M2    Bromine becomes polarised/becomes polar
OR    forms an induced dipole
OR    becomes δ+/δ–
M1 QoL – require one of these terms
Ignore “(very) negative” and “nucleophile” as applied to the double bond.
Penalise M2 for ion formation from bromine
For M2, do not credit dipole formation solely as a consequence of electronegativity
2
(ii)     Electrophilic addition
Both words needed
Accept phonetic spelling
1
(iii)     Structure for 1,2,4,5-tetrabromopentane, for example
BrCH2CHBrCH2CHBrCH2Br
OR

Must be clear that they have drawn 1,2,4,5-tetrabromopentane and does NOT need to be displayed
Credit use of “sticks” for each C-H bond
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(c)                            +
M1    Structure of CH3CHCH3
M2    (Secondary) Carbocation OR (secondary) carbonium ions
Mark independently
For M1 the positive charge must be on the central carbon atom
Penalise bond to positive charge
Penalise answers which show more than the correct carbocation e.g. the mechanism, unless the intermediate is clearly identified
Credit use of “sticks” for each C-H bond
For M2, penalise “primary” or “tertiary”
2
[12]

5.     (a)     (i)      M1 Elimination
M1 Credit “base elimination” but no other prefix.

Penalise M2 if covalent KOH
Penalise M4 for formal charge on C or Br of C−Br or incorrect partial charges on C−Br
M2 must show an arrow from the lone pair on the oxygen of a negatively charged hydroxide ion to a correct H atom
Ignore other partial charges
M3 must show an arrow from a correct C−H bond adjacent to the C−Br bond to a correct C-C bond. Only award if an arrow is shown attacking the H atom of a correct adjacent C−H bond in M2
Penalise once only in any part of the mechanism for a line and two dots to show a bond
M4 is independent provided it is from their original molecule, BUT CE=0 for the mechanism (penalise M2, M3 and M4 only) if nucleophilic substitution mechanism is shown
Maximum any 2 of 3 marks for the mechanism for wrong organic reactant or wrong organic product (if shown).
Credit the correct use of “sticks” for the molecule except for the C−H being attacked
Award full marks for an E1 mechanism in which M4 is on the correct carbocation
Penalise M4, if an additional arrow is drawn from Br eg to K+
NB These are double-headed arrows
4
(ii)     Displayed formula for 3-methylbut-1-ene

All bonds and atoms must be drawn out, but ignore bond angles
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(iii)    Position(al) (isomerism or isomer)
Penalise any other words that are written in addition to these.
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(b)    (i)      Displayed formula for 3-methylbutan-2-ol

All bonds and atoms must be drawn out, but ignore bond angles.
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(ii)     Any one from
•        Lower / decreased temperature OR cold
•        Less concentrated (comparative) OR dilute KOH
•        Water (as a solvent) / (aqueous conditions)
Ignore “pressure”.
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(iii)    Nucleophilic substitution
Both words needed - credit phonetic spelling.
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(iv)    (Strong / broad) absorption / peak in the range 3230 to 3550 cm−1 or specified value in this range or marked correctly on spectrum
Allow the words “dip” OR “spike” OR “trough” OR “low transmittance” as alternatives for absorption.
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[10]

6. (a)

(b)

(c)

(d)

	

(e)

(f)

(g)

(h)	

	

7.	

	

8.	D
9.	B
10.	C
11.	A
12.	A
13.	C
14.	C
15.	A
16.	C
17.	D
18.	D
19.	C
20.	B