A-level Chemistry Mark scheme Unit 05 - Energetics, Redox and Inorganic ...
嚜澤QA Qualifications
A-LEVEL
Chemistry
CHEM5 Energetics, Redox and Inorganic Chemistry
Mark scheme
2420
June 2016
Version: 1.0 Final
Mark schemes are prepared by the Lead Assessment Writer and considered, together with the
relevant questions, by a panel of subject teachers. This mark scheme includes any amendments
made at the standardisation events which all associates participate in and is the scheme which was
used by them in this examination. The standardisation process ensures that the mark scheme covers
the students* responses to questions and that every associate understands and applies it in the same
correct way. As preparation for standardisation each associate analyses a number of students*
scripts: alternative answers not already covered by the mark scheme are discussed and legislated for.
If, after the standardisation process, associates encounter unusual answers which have not been
raised they are required to refer these to the Lead Assessment Writer.
It must be stressed that a mark scheme is a working document, in many cases further developed and
expanded on the basis of students* reactions to a particular paper. Assumptions about future mark
schemes on the basis of one year*s document should be avoided; whilst the guiding principles of
assessment remain constant, details will change, depending on the content of a particular
examination paper.
Further copies of this Mark Scheme are available from .uk
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MARK SCHEME 每 A-LEVEL CHEMISTRY 每 CHEM5 每 JUNE 2016
Question
Marking guidance
Mark
Comments
Ignore simple / molecular
Do not allow macromolecular/giant covalent/dative/dipoledipole/Hydrogen bonds
Ignore VdW
1ai
Covalent
1
1aii
P / phosphorus / P4
1
1aiii
P4O10 + 6H2O ? 4H3PO4
1
Mark independently of 1aii
Accept multiples/fractions
Ignore state symbols
Allow ions on the RHS (? 12H+ + 4PO43-)
Allow correct equations from P4O6, P2O3 and P2O5
P4O6 + 6H2O ? 4H3PO3
P2O3 + 3H2O ? 2H3PO3
P2O5 + 3H2O ? 2H3PO4
1bi
1bii
Ionic
1
Na / Sodium
1
1biii
1
2Na + 2H2O ? 2Na+ + 2OH- + H2
Ignore giant / lattice
Allow equation to form 2NaOH
Accept multiples/fractions
Ignore state symbols
3 of 22
MARK SCHEME 每 A-LEVEL CHEMISTRY 每 CHEM5 每 JUNE 2016
1biv
1
Accept multiples/fractions
Ignore state symbols
Allow ions, but do not allow H+ only for the acid.
Na2O + 2HCl ? 2NaCl + H2O
1ci
Ionic
1
Allow ionic and covalent / ionic with covalent character
1cii
Al2O3
1
Ignore state symbols
1ciii
reacts with acids and bases
1
Allow reacts with acids and alkalis / acts as both an acid
and a base / shows acidic and basic properties
1civ
Al2O3 + 6HCl ? 2Al3+ + 6Cl- + 3H2O
Al2O3 + 6H+ ? 2Al3+ + 3H2O
1
Allow equation to form 2AlCl3 ( but not Al2Cl6)
Allow equations with other acids
Al2O3 + 2NaOH + 3H2O ? 2Na+ + 2[Al(OH)4] 每
Al2O3 + 2OH每 + 3H2O ? 2[Al(OH)4] 每
Al2O3 + 2NaOH + 7H2O ? 2Na+ + 2[Al(OH)4 (H2O)2] 每
Al2O3 + 2OH每 + 7H2O ? 2[Al(OH)4 (H2O)2] 每
1
Allow equations to form 2Na[Al(OH)4] or 2Na[Al(OH)4(H2O)2]
Allow equations with other alkalis
Allow correct equations which form [Al(OH)6]3Allow equations to form [Al(OH)x(H2O)6-x]3-x etc.
Ignore state symbols
4 of 22
MARK SCHEME 每 A-LEVEL CHEMISTRY 每 CHEM5 每 JUNE 2016
Question
Marking guidance
2ai
Mark
1
1
1
2K+(g) +2e每 + 1/2O2(g) M3
Comments
Mark each line independently, but follow one route only.
Must have state symbols, but ignore s.s. on electrons.
Penalise lack of state symbols each time.
Alternative answers
2K(g) + O(g) M3
2K(g) +1/2O2(g)
M2
2K(g) +1/2O2(g) M2
2K(s) +1/2O2(g) only M1
2K(s) +1/2O2(g) only M1
or
2K(g) + O(g) M3
2K(s) +O(g)
M2
2K(s) +1/2O2(g) only M1
5 of 22
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