rESr coDE 0221201,0
FORM TP 2006185
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ADVANCBD PROFICIENCY EXAMtrNATION
CHEMISTRY
I
hour 45 minutes
'
Candidates are advised to use the first 15 minutes for reading thlough
this paper carefully. Writing may begin during this time.
READ THE FOLLOWING INSTRUCTIONS CAREFUI.LY
l.
This paper consists of NINE questions.
2.
There are THREE questions from each Module. Answer
3.
Write answers in this booklet.
4.
ALL working must be shown in this booklet.
5.
The use of non-programmable calculators is permitted.
6.
A data booklet is provided.
ALL questions.
i',.
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rESr coDE
FORM TP 2006185
02212010
MAY/ruNEzoo6
CARIBBEAN EXAMINATIONS COUNCIL
:
.l
ADVANCED PROFICIENCY EXAMINATION
,
i
i
CHEMISTRY
UNIT
2
i
- PAPER 01
.::
NOTE TO CANDIDATES
Page
ll
-Module 3 Question 7,line 3:
)
'
"1000 g of aluminium metal" should read
"1000 kg of aluminium metal".
.\
MODULE
1
Answer ALL questions.
1.
!
Lead (II) chloride (PbCIr) is a sparingly soluble
salt.
;
(a)
Write an expression for the sblubility producr of lead (II) ch:loride.
t 2 marksl
(b)
A saturated solution of PbCl" contains 0.025 mol dm-3 at25 "C. Calculate the
-
PbCl".
K
s'P
of
[ 3 marlcs]
-3(c)
:
A student finds that on adding NaCl(aq) to a saturated solution of PbCl,
tate
,forms.
a
white precipi.
,il
'ii
r
Explain this observation.
:
[ 5 marksJ
Total 10 marks
2.
When stung by an ant, a potent mixture containing an organic acid, methanoic acid (HCOOH),
is injected into the skin. Typically, organic acids are weak acids.
(a)
(i)
Explain the meaning of the term 'weak acid'
[ 2 marks]
(ii)
Account for the sensation that occurs when stung by an ant.
[ 2 rnarks]
(b)
A sample of the mixture responsible for the sting is extracted from the ants and analysed
to determine the pH and acid concentration. The pH of the sample is2.4.
(i)
Suggest a simple method of detennining pH.
lXmarkl
-4(i
i
i
ll
i)
The acid concentration is determined by titrating the sample with a 0.05 mol
dm-3 sodiunr hydroxide solution. l0 cm3 of sodium hydroxide reacts completely
with 5 cml of the sample. Given that thg equation for the reaction between
sodium hydroxide dnd nrethanoic acid is
NaOH(aq) + HCOOH(.aq) --+ HCOO Na(aq) + H"O(l)
a)
Suggest a suitable indicator for this
-titration.
,
[ 1 marli ]
b)
Calculate tlre concentration of the acid in the sample.
)
[trmarkJ
c)
Use your answer to (ii) b) above and the pH value of the sample to
calculate the value of K for the acid.
[ 3 marks]
Total 10 marks
i
:i
3.
(a)
,
rii
;i
,i
The standard hydrogen electrode is the refqience electrode with which other elgctrodgs
I
are gompared to deGrmine standard ef ectrqpe pqtgntials' :
..
, (i),,
' i ',
,,.
j:
,
.
. .
'
.','
diagram to show hoy tfrL standard electrode potential for,the
^i'lub"ll"d
(aq)
(s),elecrrode
can be found by combining it with the sTandard
/iZn
Zn'*
i
hydrogen electrode.,
Dr,3w
[ 3 marks]
(ii)
Which of the half cells is the positive electrode?
Ilmark]
(iii)
(b)
Using rurows, indicate on the diagram drawn in (i) above, the direction in which
[Lmark]
the electrons flow through the external circuit-
AZn"* (aq) / Znis) half cell is connected to a Ag*(aq) / Ag (s) half cell as shown below
Zn (s) | Znz* (aq) :
(i)
: Ag. (aq) / Ag (s)
Write the equations for the reactions occurring at each half cell, using electrode
potentials given in the data booklet.
Positive electrode
Negative electrode
[ 2 marks]
(ii)
Calculate the standard e.m.f. of the cell.
r r ------l-r
-6
. ' :
' : ;: i ,
i,
I
i
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t,
i'
a
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A srudenr sers up the Ag* (aq)/ Ag (q) hqlf cel;t in (b) page,5, using a soliition u'f
0.it'inbl,dn'r-'eSl ions instead of I mol dm-r Ag* ions- Suggest how this wopld
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for;yourans*er.,
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Giveareason
,;'affecithe:p.m,fi:ofthepe,ll.
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ii).
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[ 2 marks]
Total 10 marl<s
MODULE
2
AnswerALL questions.
4.
The Group II elements, beryllium to barium (Be to Ba), and their compounds show distinct
trends / patterns in properties and behaviour'
(a)
Write an equation for the first ionization energy of beryllium (Be)-
Ilmark]
(b)
Using the data booklet provided, explain the trend in the first ionization energy with
atomic radii for the Group II elements.
,
(c)
t 2 marksl
Write an equation for the reaction between ONE of the Group II elernents and water.
[ 2 marksJ
l
(d)
Using standard electrode potentials, explain why the reaction in (c) would occur more
vigorously with barium (Ba) than beryllium (Be), g:iven
[Be2*
+ Z"- if
Be Eo=-l.g5V].
[ 2 marks]
(e)
Explain the variation in the solubiliry of the sulphates of Group II elements as the group
is descended. /'
[ 3 marks]
Total l0 marks
-8).
(a)
Part of the periodic table is shown in Figure
Figure
I below.
L
Write an ion of an element shown in Figure
following substances:
l,
which will react with EACH of the
(i)
Acidified aqueous silver nitrate to form
(ii)
Aqueous lead
(iii)
Aqueous potassium hydroxide to form a red-brown precipitate
(iv)
Aqueous sodium carbonate to form a white precipitate
(D
a
white precipitate
nitrate to form a yellow precipitate
[ 4 marks]
(b)
X is a powdered mixture containing a soluble and an insoluble salt. A sarnple of X
treated in the following manner:
is
I.
Water is added to X and the mixture is filtered.
11.
The residue reacts completely with dilute nitric acid and
m.
One sample of the filtrate reacts with acidified barium chloride to form a white
precipitate. Another sample reacts with aqueous ammonia and sodium hydroxide
to form a white precipitate which is soluble in excess of the reagents.
colourless gas evolvc's,
which forms a white precipitate with aqueous calcium hydroxide. The resulting
solution reacts with both aqueous ammonia and sodium hydroxide to form a
white precipitate, that does not dissolve in excess of the reagents.
a
(i)
Using the information given on page 8, deduce the possible ions present
in the
a)
residue
[ 2 marks]
b)
filtrate.
[ 2 marks]
'
(ii)
write d balanced ionic equation for the reaction between nitric
acid and
residue.
the
[ 2 marks]
Total 10 marks
6'
(a)
Transition elements exhibit special characteristics, which
distinguish them from
Group I and Group II metals. For example, transition elements
exhibit variable oxidation
states.
(i)
Determine the oxidation state of vanadium in
vo.
and
vo2*.
[ 2 marksl
(ii)
(b)
State TWO OTHER characteristics of transition elements.
Complete rhe electronic configuration of a
(i)
.
t 2 marksl
chromium arom, Cr
ls2 2sz 2pu 3s2 3pu
(ii)
Ilmark]
chromium ion, Cr3*.
ls2 2sz 2pu 3s2
3pu
Ilmark]
42212010/CAPE/F 2006
GO ON TO TIIE NEXT PAGE
,l
l0(c)
In
an_aqueous solution
complex
of chrorr
i"" rc.(Hr;;;ai,i:';";'m (III)
chloride (crclr(aq)),
chromium rorms
rhe
Deduce the likery
shape and the bond
angres in this comprex
ion.
Shape:
-llmarkl
Bond angle:
(d)
It
w
has been observerr rh6r
^
e
ak
r
y
"",
d,
[ I rnark ]
^^,_
::K"sl::ffi :l';,,|i;j
; ?:: H;,
"jJ:Ii:il,1r)
io n
s,
r
c,(H, o )u r, *(aq i s
)
[ 2 mar!.:s]
Total l0 marks
il
MODUI-E
3
Answer ALI- questions.
7.
tion of aluminium frr
for
the large-scale produclethod
(A,,o3),r0i;;;#il,l]:ffi i;J,1lliHi"#:l:'h+;*:,,1m:T?"liff
*iS;tH""
(a) Describe and explain the
use of
(i)
(ii)
(b)
EACH of the foilowing
in the Hau-Heroult process.
Cryotite
Carbon
[ 2 marks]
[ 2 marks]
Account for the requirement
of 5.6 x lOeJ of energy to
produce 1000 kg of aluminium
metal.
[ 2 marksJ
-12(c)
(i)
Calculate the theoretical yield
of alurninium expected from l900kg
of AI"O.,.
Slrow all working.
[ 3 marlcsJ
(ii)
Sr::*"n,.on
the efficiency of the process in
the extracrion of aruminium
fronr its
Ilmark]
Total l0 marks
8.
chlorofluorocarbons' cFCs, have
found application
in a variety of commerciar products
because of their special properties. -rto*"rr".,-cFCs
can
persist in the atmosphere for
years and scientists have provided
many
evidence of their a""omp'osition
productrl;;" stratosphere.
The resistance has proven to
be of concern regarding the
impact on human hearth.
(a)
ff:,1Y,3-:"H:rcial
products in which cFCs courd
be found before regularions
[ 2 marks]
(b)
State TWO properries of CFCs
that make them applicable in the products
given in (a).
[ 2 marksl
l3
(c)
"i*ib,T,?::,ff fi
(d)
".::",::,;,;ni:";"ilil:T3"andexp,ain,hesignincance
been estimated
that 3 molecule
nrnra^,,r^ of
^r
Deror-e
Jt
las
(i)
(ii)
it
is deshoy"J,'n"'a
^ _ _2 persisrs
c{Ct,
urorr
z
r".
[ 2 rnarksJ
in rhe
rrr
rne iatmosphere
for 120 year.s
Suggest
a reason fnr rh^
persistence
-_
of this
its.mot""ur*'ilLforrthe
----v cFc
vr u rr
in
teatures.
Explain the impact
of
C{CI,
the
rne atmosphere
in terms of
Iz marks]
in the atmosphere
on human health.
[ 2 marks]
Totat I0 marks
:'
-14-
g.
During,n"
r?,*:.^:jl1 hrTrn
the naturalcotrcentrations
(i)
(i
i)
(iii)
acriviries have contrib
of o^i0", of nitrogen
il;":::r:"i:T::*t.
Describe with the
aid ur
4ru
of an
ai equation how
in the arrn^"^;:::
njtro
[ 2 marksJ
oNE human. acfiviry
I?."_lltt
thar alters the atmospheric
nrrogen
and explain tne
concenration of
cne#isto,r""ii,"o i"
oxides of
: the production
of the pollutant.
Describe, *::l_,1"
aid.of an eguation,
one
oioxil. u"r-u potrutant environmr
presence of nitrogen
(iv)
ponution by artering
in;;;ffi$ir:l]."t.
ney:paper reporrs
indicate
of rhe arctic o""un
:rosslng
there is insufficient
ice. Suggest
*::l
[ 2 mari<s]
[ 3 marks]
]rli" iH:;#.",-r:ii:':jbl"
an exptanation
F;;
that occurs due
ro rhe
to comprete a surrace
ffi'}|:l#eto
Norwav because
[ 3 marks]
END OF'
Total l0 rnarks
T,EST,