OCR Chemistry A January 2011 Mark Scheme [F321]

Mark Scheme for January 2011, chemistry specification a for ocr.  Especially useful if resiting. Question paper:http://getrevising.co.uk/resources/ocr_chemistry_a_january_2011_question_paper_f321

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  • Created on: 22-05-11 12:06
Preview of OCR Chemistry A January 2011 Mark Scheme [F321]

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GCE
Chemistry A
Advanced Subsidiary GCE
Unit F321: Atoms, Bonds and Groups
Mark Scheme for January 2011
Oxford Cambridge and RSA Examinations

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OCR (Oxford Cambridge and RSA) is a leading UK awarding body, providing a wide range of
qualifications to meet the needs of pupils of all ages and abilities. OCR qualifications include
AS/A Levels, Diplomas, GCSEs, OCR Nationals, Functional Skills, Key Skills, Entry
Level qualifications, NVQs and vocational qualifications in areas such as IT, business,
languages, teaching/training, administration and secretarial skills.
It is also responsible for developing new specifications to meet national requirements and the
needs of students and teachers.…read more

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F321 Mark Scheme January 2011
Question Answer Mark Guidance
1 (a) Rb-87 has (two) more neutrons 1 ALLOW Different numbers of neutrons
ALLOW 2 neutrons
ALLOW Rb-85 has 48 neutrons AND Rb-87 has 50 neutrons
IGNORE correct references to protons and electrons
DO NOT ALLOW incorrect references to protons and
electrons
(b) The (weighted) mean mass of an atom (of an element) 3 ALLOW average atomic mass
OR DO NOT ALLOW mean mass of an element
The (weighted) average mass of an atom (of an…read more

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F321 Mark Scheme January 2011
Question Answer Mark Guidance
1 (d) Spherical OR sphere 1 DO NOT ALLOW `circular'
IGNORE unlabelled 2-D diagrams
(e) (i) Sr+(g) Sr2+(g) + e­ 1 ALLOW e for electrons
ALLOW Sr+(g) ­ e­ Sr2+(g)
DO NOT ALLOW Sr+(g) + e­ Sr2+(g) + 2e­
IGNORE state symbols for electrons
(e) (ii) 3 Use annotations with ticks, crosses ECF etc.…read more

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F321 Mark Scheme January 2011
Question Answer Mark Guidance
1 (e) (iii) 2nd IE of Rb involves removing electron from shell 2 IGNORE new shell
closer to nucleus
ALLOW There is one shell fewer in Rb(+) (than Sr+)
ALLOW Rb(+) has a smaller radius (than Sr+)
ALLOW Rb(+) loses an electron from the 4th shell AND Sr(+)
loses an electron from the 5th shell.…read more

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F321 Mark Scheme January 2011
Question Answer Mark Guidance
2 (a) (i) mol of H x A = 25.00 × 0.0500 = 1.25 × 10­3 OR 0.00125 1 ALLOW 0.0013 OR 1.3 × 10-3
mol
1000 ALLOW correct answer only without working
(ii) mol of NaOH = 1 ALLOW correct answer without working
12.50 × 0.200 = 2.5(0) × 10­3 OR 0.…read more

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F321 Mark Scheme January 2011
Question Answer Mark Guidance
2 (c) Cu(NO 3 ) 2 ·6H 2 O 1 ALLOW Cu(NO 3 ) 2 6H 2 O
ALLOW Cu(NO 3 ) 2 (H 2 O) 6
ALLOW Cu(NO 3 ) 2 .…read more

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F321 Mark Scheme January 2011
Question Answer Mark Guidance
3 (a) The ability of an atom to attract electrons 2 ALLOW `attraction of an atom for electrons'
ALLOW `pull' for `attract'
DO NOT ALLOW `element' for `atom'
in a covalent bond ALLOW `shared pair' or `bond(ing) pair' for `covalent bond'
(b) +N­F­ AND ­N­Br+ 1 ALLOW d+ / d-
DO NOT ALLOW + / ­
(c) (i) octahedral OR octahedron 1
(ii) 5 Use annotations with ticks, crosses ECF etc.…read more

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F321 Mark Scheme January 2011
Question Answer Mark Guidance
3 (c) (iii) BF 3 is symmetrical 2 IGNORE `polar bonds cancel'
The dipoles cancel out IGNORE `charges cancel'
Total 11
7…read more

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F321 Mark Scheme January 2011
Question Answer Mark Guidance
4 (a) Used to neutralise acidic soils 2 ALLOW raises the pH of the soil
IGNORE references to fertilisers
Excess will result in soils becoming too alkaline (to ALLOW pH becomes too high
sustain crop growth) IGNORE `harmful'
IGNORE `corrosive'
(b) (i) 0.00131 × 40.1 = 0.0525 g OR 5.25 × 10-2 1 ALLOW 0.053 OR 0.05253 OR 0.052531 g
IGNORE 0.05 if correct answer seen in working
DO NOT ALLOW 0.052 OR 0.…read more

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