2003 Chemistry

Higher

Finalised Marking Instructions

Page 2

Higher Chemistry

General information for markers

The general comments given below should be considered during all marking.

1 Marks should not be deducted for incorrect spelling or loose language as long as the meaning ofthe word(s) is conveyed.

Example: Answers like 'distiling' (for 'distillation') and 'it gets hotter' (for 'the temperature rises')should be accepted.

2 A right answer followed by a wrong answer should be treated as a cancelling error and no marksshould be given.

Example: What is the colour of universal indicator in acid solution?

The answer 'red, blue' gains no marks.

3 If a right answer is followed by additional information which does not conflict, the additionalinformation should be ignored, whether correct or not.

Example: Why can the tube not be made of copper?

If the correct answer is related to a low melting point, 'It has a low melting point andis coloured grey' would not be treated as having a cancelling error.

4 Full marks are usually awarded for the correct answer to a calculation on its own; the part marksshown in the marking scheme are for use when working is given. An exception is whencandidates are asked to ‘Find, by calculation, …..’.

5 A half mark should be deducted in a calculation for each arithmetic slip.

6 A half mark should be deducted for incorrect or missing units only when stated in the markingscheme. No marks should be deducted for incorrect or missing units at intermediate stages in acalculation.

7 Where a wrong numerical answer (already penalised) is carried forward to another step, nofurther penalty is incurred provided the result is used correctly.

8 Ignore the omission of one H atom from a full structural formula provided the bond is shown.

9 With structures involving an –OH or an –NH2 group, a half mark should be deducted if the 'O' or'N' are not bonded to a carbon, i.e. OH–CH2 and NH2–CH2.

10 When drawing structural formulae, a half mark should be deducted if the bond points to the'wrong' atom, eg

11 A symbol or correct formula should be accepted in place of a name unless stated otherwise inthe marking scheme.

12 When formulae of ionic compounds are given as answers it will only be necessary to show ioncharges if these has been specifically asked for. However, if ion charges are shown, they must becorrect. If incorrect charges are shown, no marks should be awarded.

C C

OH

Page 3

13 If an answer comes directly from the text of the question, no marks should be given.

Example: A student found that 0·05 mol of propane, C3H8 burned to give 82·4 kJ of energy.

C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(l)

Name the kind of enthalpy change which the student measured.

No marks should be given for 'burning' since the word 'burned' appears in the text.

14 A guiding principle in marking is to give credit for (partially) correct chemistry rather than tolook for reasons not to give marks.

Example 1: The structure of a hydrocarbon found in petrol is shown below.

Name the hydrocarbon.

Although the punctuation is not correct, '3, methyl-hexane' should gain the fullmark.

Example 2: A student measured the pH of four carboxylic acids to find out how their strength isrelated to the number of chlorine atoms in the molecule. The results are shown.

Structural formula pHCH3COOH 1·65CH2ClCOOH 1·27CHCl2COOH 0·90CCl3COOH 0·51

How is the strength of the acids related to the number of chlorine atoms in themolecule?

Although not completely correct, an answer such as 'the more Cl2, the stronger theacid' should gain the full mark.

15 Unless the question is clearly about a non-chemistry issue, eg costs in industrial chemistry, anon-chemical answer gains no marks.

Example: Why does the (catalytic) converter have a honeycomb structure?

A response such as 'to make it work' may be correct but it is not a chemical answerand the mark should not be given.

16 When it is very difficult to make a decision about a partially correct answer, a half mark can beawarded.

17 When marks have been totalled, a half mark should be rounded up.

CH3 CH2 CH CH2 CH3CH2

CH3

Page 4

2003 Chemistry Higher

Marking Scheme

Section A

1. C 11. D 21. A 31. D

2. D 12. A 22. C 32. B

3. B 13. B 23. D 33. A

4. C 14. D 24. D 34. D

5. D 15. C 25. A 35. B

6. B 16. C 26. D 36. D

7. C 17. A 27. C 37. C

8. B 18. C 28. A 38. C

9. C 19. A 29. B 39. A

10. D 20. B 30. A 40. B

Page

5

Mar

k Sc

hem

eW

orth

½W

orth

0

1.(a

)2,

3,3–

trim

ethy

lpen

tane

or 3,3,

2–tr

imet

hlyp

enta

ne(c

omm

as, d

ash

may

be

omit

ted)

1

2-m

ethy

l, 3-

dim

ethy

lpen

tane

or 3,3,

4–tr

imet

hylp

enta

neor 2,

3,3–

met

hylp

enta

ne

2,3–

met

hylp

enta

neor m

ethy

lpen

tane

(b)

cycl

oalk

anes

orri

ng s

truc

ture

orna

phth

aor

arom

atic

s (b

enze

nes)

orcy

clic

phen

ol

benz

yl h

ydro

carb

ons

1 (2)

Page

6

Mar

k Sc

hem

eW

orth

½W

orth

0

2.(a

)St

rong

or

rigi

d or

dur

able

or toug

h or

har

d or

har

d to

pun

ctur

e1

ligh

tor do

es n

ot b

urn

(b)

amid

e li

nkor pe

ptid

e li

nk1

poly

amid

eor po

lype

ptid

e

amin

o gr

oup

or amin

e gr

oup

(2)

Page

7

Mar

k Sc

hem

eW

orth

½W

orth

0

3.(a

)pl

ottin

g po

ints

cor

rect

ly a

nd jo

inin

g w

ith

a lin

e1

poin

ts n

ot jo

ined

or one

poin

t not

plo

tted

corr

ectly

or poin

ts jo

ined

by

stra

ight

line

(b)

210 Po

20

6 Pb +

He

(or

α)or

num

bers

on

rhs

any

wro

ng s

ubsc

ript

or

supe

rscr

ipt

210 Po

206 Pb

1

(c)

210

g co

ntai

n 6

x 10

23 (

atom

s)

105

g co

ntai

n ½

x 6

x 1

023 (

atom

s)

= 3

x 1

023

(½)

(½)

6 x

1023

in 1

mol

(3)

α

Page

8

Mar

k Sc

hem

eW

orth

½W

orth

0

4.(a

)an

y su

gges

tion

that

iron

for

med

is m

olte

n or

in li

quid

stat

eor

iron

is f

orm

ed (

in q

uest

ion)

or exot

herm

ican

swer

impl

ies

that

iron

flo

ws

dow

n in

to c

rack

1or ra

il m

elts

, etc

(b)

∆H re

quire

d = ∆H

1 – ∆

H2

= (

-167

6) –

(-8

25)

(½)

= -

851

kJ

(mol

-1)

(½)

(2)

Page

9

Mar

k Sc

hem

eW

orth

½W

orth

0

5.(a

)sy

nthe

sis

gas

or s

yn. g

as1

synt

hetic

gas

(b)

oxid

atio

n or

deh

ydro

gena

tion

1

(c)

(i)

1

(ii)

the

rmos

ettin

g1

ther

moh

arde

ning

(4)

CN

N

OH

H HH

CO

NH

2H

2N

NC

ON

H H

H H

CO

NH

2N

H2

Page

10

Mar

k Sc

hem

eW

orth

½W

orth

0

6.(a

)(i

)re

acta

nts

or p

rodu

cts

coul

d go

on

fire

(fl

amm

able

)or to

pre

vent

bur

ning

1

(ii)

to c

onde

nse

any

vapo

urs

(or

reac

tant

s or

pro

duct

s w

hich

eva

pora

te)

1ea

sier

to c

ontr

ol th

ete

mpe

ratu

re/c

onde

nsat

ion

or safe

r w

ay to

hea

t

(b)

1

HC

CO

CC

CC

CH

HH

HH

HH

HH

OH

HH

H

O

CH

3CH

2-O

-CC

H2C

H2C

H2C

H3

or

Page

11

Mar

k Sc

hem

eW

orth

½W

orth

0

6.(c

)1

mol

C2H

5OH

=

46

g

46 g

x 13

0 g

3.6

g x

130

x

=

7.1

2 g

or 1 m

ol C

2H5O

H =

46

g

(½)

(½)

(½)

(½)

(½)

46 g

13

0 g

3.6

g13

0 x

= 1

0.17

4 g

a

ctua

l yie

ld =

10.

174

x

= 7

.12

g

(-½

for

wro

ng o

r no

uni

ts)

(½)

(½)

(½)

(5)

70

100

70

100

3.6

g 4

6 100

70

46

6.3

Page

12

Mar

k Sc

hem

eW

orth

½W

orth

0

7.(a

)m

oles

of

Mg

=

=

0.1

65 m

ol (

½)

mol

es o

f ac

id=

=

0.2

mol

es (

½)

mol

e ra

tio =

1 m

ol M

g :

2 m

ol a

cid

Not

eno

ugh

HC

l(aq

). T

here

fore

Mg

in e

xces

s (1

)2

(b)

1

Syst

em n

ot s

eale

d

(c)

rate

– s

low

er(½

)vo

lum

e –

sam

e

(½)

1 (4)

to s

yrin

ge

wat

er

3.24

0.4 100050

x

4

Page

13

Mar

k Sc

hem

eW

orth

½W

orth

0

8.(a

)(i

)ca

rbon

yl g

roup

at e

nd o

f ca

rbon

cha

in in

ald

ehyd

eor on

ly o

ne H

att

ache

d to

car

bony

lor al

dehy

de

or keto

ne1

(ii)

blu

e (½

)or

ange

/bri

ck r

ed/b

row

n (½

)1

(iii)

C3H

6O +

H2O

2H+(a

q) +

C2H

5CO

OH

+ 2

e-1

H+(a

q) a

nd e

- on

rhs

but n

otba

lanc

ed(i

v) p

ropa

noic

(ac

id)

1

(b)

(i)

addi

tion

or redu

ctio

n1

(ii)

1 (6)

HC

CC

H

HC

NHH

OH

H

orC C

N

H3C

CH

3

OH

CC

C

O

(

C C

O C

)

H

O (

– C

HO

)C

Page

14

Mar

k Sc

hem

eW

orth

½W

orth

0

9.(a

)to

tal v

olum

e no

t kep

t con

stan

t (ch

ange

s, in

crea

ses)

or chan

ges

conc

entr

atio

n of

all

rea

ctan

ts –

not

just

pota

ssiu

m io

dide

or mor

e th

an o

ne v

aria

ble

chan

ged

1

(b)

use

mor

e ac

cura

te m

easu

ring

cyl

inde

rs (

or s

yrin

ges)

for

smal

ler

volu

mes

in s

tep

1or st

art t

imer

whi

le a

ddin

g hy

drog

en p

erox

ide

(whe

n ha

lfof

the

pero

xide

has

bee

n ad

ded)

or put w

hite

tile

/pap

er b

elow

bea

ker

or repe

at e

xper

imen

t (a

ny tw

o)1 (2

)

Page

15

Mar

k Sc

hem

eW

orth

½W

orth

0

10.

(a)

rate

of

forw

ard

reac

tion

equa

ls r

ate

of b

ackw

ard

reac

tion

or conc

entr

atio

ns o

f re

acta

nt(s

) an

d pr

oduc

t(s)

are

con

stan

t1

rate

s ar

e co

nsta

nt

(b)

iodi

ne w

ill g

o fr

om c

hlor

ofor

m la

yer

(bot

tom

laye

r) in

toth

e K

I la

yer

(top

laye

r) to

res

tore

equ

ilibr

ium

or equi

libr

ium

mov

es to

left

(ra

te o

f ba

ckw

ard

reac

tion

incr

ease

s)1

(c)

0.3

g of

iodi

ne is

dis

solv

ed in

chl

orof

orm

(½

)

ther

efor

e, c

once

ntra

tion

= =

30

g l-1

(½

)

(uni

ts n

ot n

eces

sary

)1 (3

)

01.03.0

Page

16

Mar

k Sc

hem

eW

orth

½W

orth

0

11.

(a)

line

sho

uld

go u

p to

+ 7

5(½

)

line

sho

uld

then

go

dow

n to

– 2

6(½

)1

(b)

(i)

het

erog

eneo

us1

(ii)

sam

e st

artin

g le

vel

low

er p

eak

(½)

sam

e fi

nish

ing

leve

l(½

)1

(c)

(i)

=

1.2

cm

3 s-1

(-½

for

wro

ng o

r no

uni

ts)

110

24 - 36

Page

17

Mar

k Sc

hem

eW

orth

½W

orth

0

11(c

)(i

i)

1 m

ol O

2 fr

om 2

mol

of

H2O

2 (½

)1

mol

H2O

2 =

34

g (

½)

24 li

tres

O2

from

2 x

34

g of

H2O

2 (½

)

0.04

litr

es f

rom

=

0.1

13 g

(½

)

( -

½ f

or w

rong

or

no u

nits

)

2 (6)

24

0.04

x

68

Page

18

Mar

k Sc

hem

eW

orth

½W

orth

0

12.

(a)

prop

ane

mol

ecul

es a

re h

eld

toge

ther

by

wea

k fo

rces

or etha

nol m

olec

ules

are

hel

d to

geth

er b

y st

rong

for

ces

(1)

the

inte

rmol

ecul

ar f

orce

s in

pro

pane

are

van

der

Waa

ls’

forc

es(½

)

the

inte

rmol

ecul

ar f

orce

s in

eth

anol

are

hyd

roge

n bo

nds

(½)

van

der

Waa

ls’

forc

es a

re d

ue to

mom

enta

rydi

spla

cem

ent o

f el

ectr

ons

betw

een

atom

s(½

)(½

)

hydr

ogen

bon

ding

ari

ses

beca

use

the

O-H

bon

d is

hig

hly

pola

rise

d (t

here

is a

larg

e di

ffer

ence

in th

eel

ectr

oneg

ativ

itie

s of

O a

nd H

)(½

)

the

smal

l pos

itive

cha

rge

on H

and

sm

all n

egat

ive

char

geon

O s

tron

gly

attr

act

(½)

(4)

Page

19

Mar

k Sc

hem

eW

orth

½W

orth

0

13.

(a)

[H+(a

q)]

= 1

x 1

0-8 m

ol l-1

(uni

ts n

ot n

eces

sary

)

1

(b)

this

mus

t be

the

salt

of a

str

ong

alka

li (

or b

ase)

and

aw

eak

acid

or alka

li s

tron

ger

than

aci

d1

(c)

HC

N o

r C

NH

1 (3)

Page

20

Mar

k Sc

hem

eW

orth

½W

orth

0

14.

(a)

Seaw

ater

(so

dium

chl

orid

e), c

arbo

n di

oxid

e, a

mm

onia

(- ½

for

any

om

issi

on)

or corr

ect f

orm

ulae

1

(b)

CaC

O3

CaO

+ C

O2

∆

H =

+ve

(½)

C +

O2

CO

2∆H

= -v

e

(½)

1

use

of e

xoth

erm

ic/

endo

ther

mic

(c)

Ca(

OH

) 2 +

2N

H4C

lC

aCl 2

+ 2

H2O

+ 2

NH

31

Page

21

Mar

k Sc

hem

eW

orth

½W

orth

0

14.

(d)

mag

nesi

um c

arbo

nate

is in

solu

ble

or mag

nesi

um c

arbo

nate

for

ms

a pr

ecip

itate

1

(e)

CO

2 or

NH

3 or

NH

4Cl r

ecyc

led

(reu

sed)

or coke

add

ed to

lim

esto

ne to

pro

vide

ene

rgy

by r

eact

ing

wit

h O

2 fr

om a

ir (

or b

y bu

rnin

g)or ca

lciu

m c

hlor

ide

prod

uced

as

by-p

rodu

ctor (s

ome)

rea

ctan

ts f

ound

nat

ural

ly (

easi

ly o

btai

ned,

che

ap)

or cont

inuo

us p

roce

ss

recy

clin

g oc

curs

or no w

aste

pro

duct

sor no

n-po

llutin

gor by

-pro

duct

s ar

e us

eful

(any

two,

1 m

ark

each

)2 (6

)

Page

22

Mar

k Sc

hem

eW

orth

½W

orth

0

15.

(a)

hydr

olys

is (

hydr

olys

ing)

1di

gest

ion

or dena

turi

ng

(b)

(i)

1

(ii)

A

CB

on

rhs

(ign

ore

dist

ance

s; o

rder

mus

t be

corr

ect)

AB

C, B

AC

, CA

B o

n rh

sor C

BA

on

lhs

(w

orth

1 m

ark)

2

BC

Aor C

BA

on

rhs

(4)

HC

H

CO

O–

NH

2

Page

23

Mar

k Sc

hem

eW

orth

½W

orth

0

16.

(a)

Q =

It =

0.5

x 1

4 x

60 (

½)

= 4

20 C

(½

)

2H+ +

2e-

H

2

n =

2

(½)

2 x

96 5

00 C

1

mol

H2 (½

)

420

C0.

052

litre

s

2 x

96 5

00 C

x

0.05

2 (½

)

= 2

3.89

5 lit

res

(½)

(– ½

for

wro

ng o

r no

uni

ts)

3

(b)

add

vari

able

res

isto

r (t

o ke

ep c

urre

nt c

onst

ant)

or use

plat

inum

ele

ctro

des

1

add

a de

vice

to k

eep

cons

tant

curr

ent

(4)

[EN

D O

F M

AR

KIN

G I

NST

RU

CT

ION

S]

2 x

96 5

00

420