Introduction to

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Chapter 8 Introduction to Clustering Procedures Chapter Table of Contents OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 CLUSTERING VARIABLES . . . . . . . . . . . . . . . . . . . . . . . . . . 99 CLUSTERING OBSERVATIONS . . .
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  • macro plotclus
  • proc cluster
  • equal size
  • clusters
  • observations
  • methods
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  • method
  • data
Published : Tuesday, March 27, 2012
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Origin : thepaperbank.co.uk
Number of pages: 107
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GCE



Chemistry

Advanced GCE A2 7882
Advanced Subsidiary GCE AS 3882




Mark Schemes for the Units

June 2007
































3882/7882/MS/R/07
Oxford Cambridge and RSA Examinations Downloaded from www.thepaperbank.co.uk

OCR (Oxford Cambridge and RSA Examinations) is a unitary awarding body, established by the
University of Cambridge Local Examinations Syndicate and the RSA Examinations Board in
January 1998. OCR provides a full range of GCSE, A level, GNVQ, Key Skills and other
qualifications for schools and colleges in the United Kingdom, including those previously
provided by MEG and OCEAC. It is also responsible for developing new syllabuses to meet
national requirements and the needs of students and teachers.

This mark scheme is published as an aid to teachers and students, to indicate the requirements
of the examination. It shows the basis on which marks were awarded by Examiners. It does not
indicate the details of the discussions which took place at an Examiners’ meeting before marking
commenced.

All Examiners are instructed that alternative correct answers and unexpected approaches in
candidates’ scripts must be given marks that fairly reflect the relevant knowledge and skills
demonstrated.

Mark schemes should be read in conjunction with the published question papers and the Report
on the Examination.

OCR will not enter into any discussion or correspondence in connection with this mark scheme.

© OCR 2007

Any enquiries about publications should be addressed to:

OCR Publications
PO Box 5050
Annesley
NOTTINGHAM
NG15 0DL

Telephone: 0870 870 6622
Facsimile: 21
E-mail: publications@ocr.org.uk

Oxford Cambridge and RSA Examinations Downloaded from www.thepaperbank.co.uk
CONTENTS


Advanced GCE Chemistry (7882)

Advanced Subsidiary GCE Chemistry (3882)


MARK SCHEME FOR THE UNITS

Unit Content Page

2811 Foundation Chemistry 1
2812 Chains and Rings 9
2813/01 How Far? How Fast? / Experimental Skills 1 15
Written Paper
2813/03 Skills 1 21
Practical Examination
2814 Chain, Rings and Spectroscopy 29
2815/01 Trend and Patterns 45
2815/02 Biochemistry 49
2815/03 Environmental Chemistry 57
2815/04 Methods of Analysis and Detection 63
2815/05 Gases, Liquids and Solids 69
2815/06 Transition Elements 75
2816/01 Unifying Concepts in Chemistry/Experimental Skills 83
2 Written Paper
2816/03 e93
2 Practical Examination

* Grade Thresholds 100

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Mark Scheme 2811
June 2007






1 9
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2811 Mark Scheme June 2007

ADVICE TO EXAMINERS ON THE ANNOTATION OF SCRIPTS

1. Please ensure that you use the final version of the Mark Scheme.
You are advised to destroy all draft versions.

2. Please mark all post-standardisation scripts in red ink. A tick ( ) should be used for each
answer judged worthy of a mark. Ticks should be placed as close as possible to the point
in the answer where the mark has been awarded. The number of ticks should be the
same as the number of marks awarded. If two (or more) responses are required for one
mark, use only one tick. Half marks (½) should never be used.

3. The following annotations may be used when marking. No comments should be written on
scripts unless they relate directly to the mark scheme. Remember that scripts may be
returned to Centres.

x = incorrect response (errors may also be underlined)
^ = omission mark
bod = benefit of the doubt (where professional judgement has been used)
ecf = error carried forward (in consequential marking)
con = contradiction (in cases where candidates contradict themselves in the same
response)
sf = error in the number of significant figures

4. The marks awarded for each part question should be indicated in the margin provided on
the right hand side of the page. The mark total for each question should be ringed at the
end of the question, on the right hand side. These totals should be added up to give the
final total on the front of the paper.

5. In cases where candidates are required to give a specific number of answers, (e.g. ‘give
three reasons’), mark the first answer(s) given up to the total number required. Strike
through the remainder. In specific cases where this rule cannot be applied, the exact
procedure to be used is given in the mark scheme.

6. Correct answers to calculations should gain full credit even if no working is shown, unless
otherwise indicated in the mark scheme. (An instruction on the paper to ‘Show your
working’ is to help candidates, who may then gain partial credit even if their final answer is
not correct.)

7. Strike through all blank spaces and/or pages in order to give a clear indication that the
whole of the script has been considered.

8. An element of professional judgement is required in the marking of any written paper, and
candidates may not use the exact words that appear in the mark scheme. If the science is
correct and answers the question, then the mark(s) should normally be credited. If you are
in doubt about the validity of any answer, contact your Team Leader/Principal Examiner for
guidance.


2 9
9
9
9
9
9
9
9
9
9
9
9
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2811 Mark Scheme June 2007


/ = alternative and acceptable answers for the same marking point Abbreviations,
; = separates marking points annotations and
NOT = answers which are not worthy of credit conventions
( ) = words which are not essential to gain credit
used in the
= (underlining) key words which must be used to gain credit
Mark Scheme ecf = error carried forward
AW = alternative wording
ora = or reverse argument

Question Expected answers Marks
1 (a)


1, 2 or 3 p orbitals are OK [2]

(b) d orbital 2
p sub-shell 6
[3] 3rd shell 18
(c) (i)


(ii)








2s and 2p labels Ignore any superscripted numbers.
8 electrons in correct levels with arrows correctly shown
[2]
(d) (i) Energy change when each atom in 1 mole
of gaseous atoms
[3] loses an electron (to form 1 mole of gaseous 1+ ions).

2+ 3+ − (ii) [2] O (g) ⎯→ O (g) + e 99
1 mark for correct species; 1 mark for state symbols
No charge required on electron.
Ignore (g) on e
[2]
Large difference between 6th and 7th IEs
(iii) marking a different shell (closer to nucleus)
allow ‘inner shells’/new shell/full shell/first shell
marking points independent.
not sub-shell or orbital
Total: 14

3 9
9
9
9
9
9
9
9
9
9
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2811 Mark Scheme June 2007


/ = alternative and acceptable answers for the same marking point Abbreviations,
; = separates marking points annotations and
NOT = answers which are not worthy of credit conventions
( ) = words which are not essential to gain credit
used in the
= (underlining) key words which must be used to gain credit
Mark Scheme ecf = error carried forward
AW = alternative wording
ora = or reverse argument

Question Expected answers Marks
2 (a) (i) mass = 0.0500 x 23.0 = 1.15 g [1]

(ii) moles H = 0.0250 2
3 [2] volume H = 0.0250 x 24 = 0.600 dm 2
ecf from calculated moles H 2

3 [1] 0.0500 mol in 50.0 cm
−3 (iii) concentration = 0.0500 x 20 = 1.00 mol dm
+ (b)
2−
Na


+ O

Na



Also accept Na with full shell as long as it contains ‘x’s
(as in example above)

Ignore any inner shells

correct dot and cross [2]
correct charges

(c) (i) 2Na + O ⎯→ Na O [1] 2 2 2

(ii) [1] Na O + 2H O ⎯→ H O + 2NaOH 2 2 2 2 2

correct covalent bonds shown
(iii) [2] electron count (14) for rest of molecule correct

Total: 10

4 9
9
9
9
9
9
9
9
9
9
9
9
9
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2811 Mark Scheme June 2007


/ = alternative and acceptable answers for the same marking point Abbreviations,
; = separates marking points annotations and
NOT = answers which are not worthy of credit conventions
( ) = words which are not essential to gain credit
used in the
= (underlining) key words which must be used to gain credit
Mark Scheme ecf = error carried forward
AW = alternative wording
ora = or reverse argument

Question Expected answers Marks
+ 3 (a) add AgNO /add Ag 3
ignore ammonia
white (precipitate)/goes white/precipitate that dissolves in
dilute NH (aq) 3

+ − [3] Ag + Cl ⎯→ AgCl
(ignore state symbols)
(b) add NaOH
[2]
Cl + 2NaOH ⎯→ NaCl + NaClO + H O 2 2

or partial or completely ionic equation:
+ – –Cl + 2NaOH ⎯→ 2Na + ClO + Cl + H O/ 2 2
– – –Cl + 2OH ⎯→ ClO + Cl + H O 2 2

(c) number of electrons
/electron shells increases down group

van der Waals’ forces
/induced dipole–dipole interactions
[3]
forces greater Cl < Br < I 2 2 2
(d) (i) (trigonal) pyramidal [1]

(ii) electron pairs repel/bonds repel
/electron pairs get as far apart as possible

lone pairs repel more/forces ‘them’ closer

[3] 4 electron pairs surround central atom or N
/diagram with 3 bonds and a lone pair
Total: 12

5 9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
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2811 Mark Scheme June 2007


/ = alternative and acceptable answers for the same marking point Abbreviations,
; = separates marking points annotations and
NOT = answers which are not worthy of credit conventions
( ) = words which are not essential to gain credit
used in the
= (underlining) key words which must be used to gain credit
Mark Scheme ecf = error carried forward
AW = alternative wording
ora = or reverse argument











Question Expected answers Marks
4 (a) (i) They have different numbers of protons/
+ + [1] Ba has one more proton/Ba has 56 p ; Cs has 55 p
(ignore electrons: any mention of ‘neutrons’ is wrong)
[1]
(ii) s

Cs to Ba: nuclear charge increases/more protons
(iii) electrons are in: the same shell/sub-shell/orbital
[3] /similar shielding/same shielding
attraction increases/pull increases …….ORA

[2] smaller
shell has been lost/less shielding/less electron
(iv) repulsion/proton : electron ratio larger
mark separately
(b) (i) loss (of electrons) [1]

(ii) Ba
[2] 0 → (+)2 (accept 2+)

Original solution contains ions/there are mobile ions
(iii) Charge carriers removed as reaction takes place
[2] /as solid forms/ as BaSO forms/as water forms 4
(c) M(BaO) = 137 + 16 = 153
moles BaO = 500/153 or 3.268 mol
moles Ba = 3.268/2 or 1.634
mass Ba formed = 1.634 x 137 = 224 g

accept 223.856209/223.86/223.9 g.
if 6 mol BaO forms 3 mol Ba, award 3rd mark

[4] Alternative method
mass 6BaO=918 g
mass 3Ba = 411 g
1g BaO forms 411/918 g Ba
500 g BaO forms 223.856209/223.86/223.9 g Ba
Total: 16
6

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