GCE

Edexcel GCE
Chemistry (8080, 9080)
6241/01

Summer 2005

Mark Scheme (Results)

Chemistry (8080, 9080)
Edexcel GCE
1 (a) Mg + ½ O2 → MgO
IGNORE state symbols (1 mark)
ALLOW multiples

(b) Correct number of electrons on both ions (must include inner shell) (1)
Drawn or “2,8”

Correct charges on each ion (1)

Free standing marks

ACCEPT all dots/ crosses or combination (2 marks)

Max 1 if elements not identified

(c) (Electrostatic) attraction between positive ions and electrons (1)

Symbol with correct charge can be specified
NOT nuclei/ protons for positive ions
NOT held together for attraction

Electrons delocalised / sea of electrons free moving (1)

are mobile / can move / flow (under a potential difference) (1)

NOT “free” on its own
NOT carry the charge (3 marks)

Total (6 marks)

1
2 (a) Gas / g green/pale green/yellow (1)
Liquid / l brown/red-brown / orange / red-orange NOT red alone (1)
Solid / s (dark) grey ALLOW black NOT purple (1)
IGNORE shiny / silver
Any combination of allowed colours (3 marks)

(b) (i) KCl + H2SO4 → KHSO4 + HCl

OR
2KCl + H2SO4 → K2SO4 + 2HCl
ALLOW multiples
IGNORE state symbols (1 mark)

(ii) Oxidation numbers: -1 (+) 6 / (+) VI

0 (+) 4 / (+) IV
Charge can be either side of number
(1) mark for any two correct oxidation numbers (2)

Oxidising Agent: (concentrated) H2SO4 (1)

NOT dilute

Oxidation no. of bromine / bromide / Br changes from -1 to 0 / rises

OR
Oxidation number of sulphur/ S changes from +6 to +4 / falls (1)

ALLOW T.E. for incorrect oxidation numbers in the correct direction (4 marks)
only
IGNORE electrons if in correct direction
4th mark not awarded if incorrect oxidising agent given EXCEPT sulphur
Total 8 marks

2
3 (a) (i) (1s2)2s22p63s23p64s2
OR
(1s2)2s22p63s23p63d04s2
OR
(1s2)2s22p63s23p64s23d0
ALLOW subscript numbers in place of superscripts

2p6 ≡ 2px22py22pz2 numbers must be superscript

3p6 ≡ 3px23py23pz2 numbers must be superscript
(1 mark)
IGNORE caps

(b) (i) Energy/ enthalpy / heat energy change / required per mole (1)
NOT evolved
for the removal of 1 electron (1)

from gaseous atoms NOT molecules (1)

OR
X(g) Æ X+(g) + e- states required for 2nd and 3rd marks (2)
Can be actual symbol of an element
ACCEPT - e(-) (3 marks)

(ii) (Even though) there is a greater nuclear charge / number of

protons
OR nuclear charge increases down the group (1)

outer / valency electron(s) further from nucleus NOT “shell” on

its own (1)

and more shielded OR more (filled) inner shells/electrons (1) (3 marks)

(c) (i) Similarity: number of protons (proton number) (1)

IGNORE electrons
NOT atomic number

Difference: number of neutrons

[correct numbers can be given] (2 marks)
NOT atomic mass or number of nucleons (1)

(ii) (24 x 78.6) + (25 x 10.1) + (26 x 11.3)

100 = 24.3

Method (1)
Answer must be to 3 SF (1)
Correct answer to 3 SF with some working (2)
IGNORE g or g mol-1 other wrong units lose a mark (2 marks)

Total 11 marks

3
4 (a) (i) Na → Na+ + e(-) OR Na – e(-) → Na+ (1)
½ Cl2 + e(-) → Cl− (1)
IGNORE state symbols
ALLOW multiples
NOT Cl + e(-) → Cl−
NOT Cl → Cl− - e(-)
NOT ½ Cl2 → Cl− - e(-) (2 marks)

(ii) Na + ½ Cl2 → NaCl / Na+Cl- NOT Na+ + Cl-

Stand alone but not consequential on incorrect half equations
ALLOW multiples
IGNORE state symbols (1 mark)

(b) (i) (bonding is) ionic / electrovalent

NOT electrostatic (1 mark)

(ii) Diagram shows alternating cation and anion (1)

in a correct 3-D pattern (1)

Key to diagram not necessary but must be recognisable differences

If Na / Cl in diagram OK, but if state “atoms” max 1 (2 marks)

(c) (i) pair of electrons shared (by two atoms)

OR
overlap of partially filled atomic orbitals (1 mark)
NOT diagram on its own

(ii) Melting BCl3 requires breaking van der Waals’ / dispersion / London /
dipole-dipole / induced dipole – induced dipole / intermolecular
forces / interactions (1)

NOT Permanent dipole

Melting NaCl requires breaking/overcoming ionic bonds /

(electrostatic) attractions between ions (1)
NOT just breaking the ionic lattice

BCl3 forces weaker than NaCl forces (1)

so less energy required to break BCl3 forces / intermolecular forces are

weaker than ionic bonds. OR Correct argument based on high melting
point of NaCl (1) (4 marks)

If in comparison :
Hydrogen bonding max 2
NaCl covalent max 2
st
max 2 ≡ negate 1 correct answer, score next two

BCl3 covalent max 1

max 1 ≡ negate two correct answers, score third
Total 11 marks

4
5 (a) (i) K(s)+H2O(l) → KOH (aq) + ½ H2 (g) / K+(aq) + OH-(aq) + ½ H2(g)

Balanced equation (1)

State symbols on correct formulae only (1)
ALLOW multiples (2 marks)

(ii) bubbles / effervescence / fizzing /hissing

floats/moves (on surface)
Melts /forms a sphere
Gets smaller / disappears /dissolves Any two
Catches fire / lilac flame / explodes

IGNORE forms a solution

IGNORE reference to noise
NOT “see a gas” (2 marks)

(b) (i) % of oxygen = 45.1% (1)

54.9/39 = 1.41 and 45.1/16 = 2.82 (1)
1.41/1.41 = 1 and 2.82/1.41 = 2 (hence KO2) / 1.41 : 2.82 ≡ 1 : (1)
2

MUST have some working (3 marks)

Correct inductive reasoning (3)

(ii) -0.5 / - ½ / -.5 (1 mark)

(c) KNO3 because K+ / potassium ion has larger radius / is larger - ion essential (1)

but same charge - stated or K+ and Li+ given (1)

[lower charge density scores 1 out of the first two marks]
“Charge density” on its own (1) UNLESS term is explained (2)

polarises/distorts nitrate/negative ion/anion less (1)

OR weakens bonds in nitrate less
NOT weakens ionic bond
If LiNO3 more stable (0) (3 marks)

Total 11 marks

5
6 (a) (i) moles silicon = 10/28 = 0.357 (1)
moles SiCl4 = 0.357 (1)
mass = 0.357 x 170 = 60.7 / 60.69 (g) ALLOW 2- 4 SF (1)
OR by mass ratio
Units not required but if given must be correct.
Correct answer with some recognisable working (3)
Correct answer with no working (1) (3 marks)

(ii) moles chlorine = 2 x 0.357 moles Si x2 (1) (1)

3
∴ vol = 0.714 x 24.0 = 17.1 (dm ) moles Cl2 x 24 (1) (1)
ALLOW TE from (i)
ALLOW 2 – 4 SF
Units not required, but if given must be correct
Correct answer with some recognisable working (2)
Correct answer with no working (1)

Penalise SF once only across (i) and (ii)

Penalise units once across (i) and (ii) (2 marks)

ratio 10/28 10/28 10/28 10/28

= 0.357 = 0.36 = 0.4
loses SF mark
mass 60.69 60.71 61.2 68

vol 17.14 17.14 17.3 19.2

6
(b)

(1)

Wedges not required e.g.

Atoms can be represented by circles etc provided there are 4 of one type and
1 of another

tetrahedral (1)

Any angle in range 109 – 109.5 ° (1)

degree symbol can be shown on diagram

4 (bond) pairs of electrons / 4 bonding pairs (1)

NOT bonds
NOT atom
NOT groups of electrons

Repel to position of minimum repulsion / potential energy NOT “Equal

repulsion” (1)
OR Repel to position of maximum separation

4th mark cannot be awarded if atoms referred to (5 marks)

7
(c) (i) Si and Cl have different electronegativities / Cl attracts the bonding (1 mark)
electrons very / more strongly / Si less electronegative than Cl / Cl
very electronegative

(ii) symmetrical molecule / chlorines equally spaced (1)

bond polarities / dipoles / vectors cancel

OR
Centres of positive and negative charge coincide / vectors cancel. (1) (2 marks)

Total 13 marks

TOTAL FOR PAPER: 60 MARKS