CHM 112 / Page 1 of 13
SEMESTER
Examination Paper
(COVER PAGE)
Session
:
August 2002
Programme
:
Cambridge A-Level Programme
Course
:
CHM 112 : Chemistry 2
Date of Examination
:
October 31, 2002
Time
:
4.00 – 6.00 p.m
Duration
:
2 Hours
Special Instructions
:
Reading Time
:
Nil
This paper consists of TWO (2) sections. Attempt ALL questions from Section A and answer ALL
from Section B in the answer booklet provided. All questions carry equal marks.
Materials permitted
:
Calculator
Materials provided
:
Data Booklet & OMR Sheet
Examiner(s)
:
Kuldip Singh and Subramaniam P
Moderator
:
Subramaniam P
This paper consists of 13 printed pages, including the cover page.
CHM 112 / Page 2 of 13
INTI COLLEGE
MALAYSIA
CAMBRIDGE A-LEVEL PROGRAMME
CHM 112 : CHEMISTRY 2
SEMESTER EXAMINATION : AUGUST 2002 SESSION
This paper consists of TWO (2) sections. Attempt ALL questions from Section A and
answer ALL from Section B in the answer booklet provided. All questions carry equal
marks.
SECTION A
1.
(40 marks)
Two diatomic gases, X2 and Y2, react as follows
X 2 (g) + Y2 (g)
2 X Y(g)
A mixture containing 0.5 moles each of X2 and Y2 is heated in a closed container and
the reaction allowed to reach equilibrium. The graph shows how the number of moles
of each gas varies with time.
What is the value of the equilibrium constant Kc for this reaction?
A.
B.
C.
D.
2.
1.5
3
9
18
The standard electrode potentials of Ag+(aq) / Ag(s) and Zn2+(aq) / Zn(s) are + 0.80 V and
–0.76V, respectively. Which of the following conclusions can be drawn from these
data?
A.
B.
C.
D.
Silver displaces zinc from a solution containing zinc ions.
Silver is an oxidising agent.
Zinc has a greater tendency than silver to form positively charged ions.
Zinc ions can act as a reducing agent.
CHM 112 / Page 3 of 13
3.
When a large current was passed through acidified aqueous copper (11) sulphate, there
was simultaneous liberation, at the cathode, of x mol of copper and y dm3 of hydrogen
(measured at s.t.p).
How many moles of electrons passed through the solution?
A.
B.
C.
D.
4.
The extraction of aluminium involves the electrolysis of purified aluminium oxide in
cryolite, Na3 AlF6. What is the main purpose of the cryolite?
A.
B.
C.
D.
5.
y
22.4
y
x+
11.2
y
x+
5.6
y
2x +
11.2
x+
To prevent oxidation of the anode
To provide an additional source of aluminium
To prevent the oxidation of the cathode carbon
To increase the electrical conductivity of the molten mixture
If the reaction
P+Q→R+S
is described as being of zero order with respect to P, it means that
A.
B.
C.
D.
P is catalyst in this reaction
no P molecules possess sufficient energy to react.
the concentration of P does not change during the reaction.
the rate of reaction is independent of the concentration of P.
CHM 112 / Page 4 of 13
6.
In the conversion of compound X into compound Z, it was found that reaction
proceeded by way of compound Y, which could be isolated. The steps involved were:
X → Y; ∆H, positive
Y → Z; ∆H, negative
Which reaction profile fits these data?
7.
Lead is the final product formed by a series of changes in which the rate-determining
stage is the radioactive decay of uranium – 238. This radioactive decay is a first-order
reaction with a half-life of 4.5 x 109 years.
What would be the age of a rock sample, originally lead-free, in which the molar
proportion of uranium to lead is now 1 : 3?
A.
B.
C.
D.
8.
1.5 x 109 years
2.25 x 109 years
4.5 x 109 years
9.0 x 109 years
Which of the following sets contains a basic, an acidic and an amphoteric oxide?
A.
B.
C.
D.
Al2O3, SiO2, P4O10
MgO, Al2O3, P4O10
MgO, P4O10, SO3
Na2O, MgO, Al2O3
CHM 112 / Page 5 of 13
9.
Which change is true for the elements barium, calcium and magnesium, with
decreasing atomic number?
A.
B.
C.
D.
10.
11.
Which element is in Group II of the Periodic Table?
element
melting point / °C
Density / g cm-3
A
B
C
D
98
113
649
1744
0.97
2.07
1.74
11.3
Electrical
conductivity / ohm-1
m-1
2.4 x 107
5.0 x 10-16
2.2 x 107
6.0 x 107
The ions P3-, S2- and Cl- have radii 0.212 nm, 0.184 nm and 0.181 nm respectively.
Which one of the following correctly explains the decrease in radius in going from P3to Cl–?
A.
B.
C.
D.
12.
The ionization energy decreases
The elements become more powerful reducing agents
The lattice energy of the oxides becomes greater
The sulphates become less soluble.
increase in the total number of electrons and in the nuclear charge
an increase in the total number of electrons with the nuclear charge remaining
constant
a constant total number of electrons and an increase in the nuclear charge
a decrease in the total number of electrons with the nuclear charge remaining
constant.
Which one of the following sets of solid elements A, B, C or D, includes a giant
metallic structure, a macromolecular structure and a simple molecular structure?
A.
B.
C.
D.
Na Mg Al
Mg Al Si
C Si Sn
Al Si S
CHM 112 / Page 6 of 13
13.
Fluorine is above chlorine in Group VII. Which one of the following statements about
fluorine and fluorine compounds is correct?
A.
B.
C.
D.
14.
An excess of aqueous silver nitrate is added to aqueous barium chloride, and the
precipitate is removed by filtration. What are the main ions in the filtrate?
A.
B.
C.
D.
15.
Ag+ and NO3- only
Ag+, Ba2+ and NO3Ba2+ and NO3- only
Ba2+, NO3- and Cl-
Why can silicon tetrachloride be hydrolysed by water whereas carbon tetrachloride
cannot?
A.
B.
C.
D.
16.
The electronegativity of fluorine is less than that of the other Group VII
elements.
Fluorine is the most powerful oxidizing agent of the Group VII elements.
Hydrogen fluoride is the strongest acid of all the Group VII hydrides.
Hydrogen fluoride is easily decomposed to its elements.
The Si - Cl bond is more polar than the C - Cl bond.
The carbon tetrachloride and silicon tetrachloride molecules have different
shapes.
The covalent bonds in silicon tetrachloride are weaker than those in carbon
tetrachloride.
Silicon can use available d orbitals whereas carbon cannot.
Which one of the following changes occurs in Group IV as the atomic number
increases?
A.
B.
C.
D.
The oxides become more basic
The hydrides become more stable to heat.
The electronegativity increases.
The melting point of the tetrachloride decreases.
CHM 112 / Page 7 of 13
17.
A sales leaflet claims that ‘applications of a solution of ammonium sulphate, which is
acidic, improve the growth of acid-loving rhododendron bushes both by increasing the
availability of nitrogen and also by increasing the pH of the soil’.
What is wrong with this statement?
A.
B.
C.
D.
18.
The gaseous oxides of nitrogen have positive enthalpy changes of formation. Which
factor is likely to make the most significant contribution to these enthalpy changes?
A.
B.
C.
D.
19.
Aqueous ammonium sulphate is not acidic
Ammonium sulphate does not dissolve in water.
To be a fertiliser, nitrogen is needed in its oxidised form (nitrate) and not its
reduced form (ammonium)
The pH of the soil will be reduced, not increased.
The high electron affinity of nitrogen atoms.
The high bond energy of the nitrogen molecule, N2
The high electron affinity of oxygen atoms.
The similar electronegativities of oxygen and nitrogen.
Each of the following equilibria is subjected to two changes carried out separately:
(i)
(ii)
the pressure is reduced at constant temperature.
the temperature is increased at constant pressure.
For which equilibrium will both of these changes result in a increase in the proportion
of products?
∆H = +53 kJ mol-1
A.
H 2 (g) + I 2(g)
B.
4 NH 3(g) + 502 (g)
C.
N 2 (g) + 3H 2 (g)
2 NH 3(g)
∆H = -92 kJ mol-1
D.
N 2O 4 (g)
2 NO 2 (g)
∆H = +57 kJ mol-1
2 HI(g)
4 NO(g) + 6 H2O(g) ∆H = -950 kJ mol-1
CHM 112 / Page 8 of 13
20.
Which graph correctly describes a trend found in the halogen group?
SECTION B : Answer ALL questions.
1.
(a)
The melting points of four chlorides are given below:
Compound
sodium chloride
aluminium chloride
carbon tetrachloride
silicon tetrachloride
(i)
(ii)
Formula
NaCl
AlCl3
CCl4
SiCl4
m.p. (°C)
801
178
–23
–70
Briefly relate these melting points to the structure of, and bonding in,
each of these chlorides.
(4 marks)
Describe the reaction, if any, of each of these four chlorides with water,
stating the approximate pH of any solution formed, and writing a
balanced equation for any reaction that takes place. Offer an
explanation for any differences that occur in their reactivities.
(4 marks)
CHM 112 / Page 9 of 13
(b)
A spray used to relieve the pain and swelling caused by insect stings contains
aluminium sulphate, Al2 (so4)3 as its active ingredient. A 5.000 g sample of
the spray was dissolved in water and an excess of aqueous barium chloride was
added. The precipitated barium sulphate weighted 2.047g.
Calculate the percentage of aluminium sulphate in the spray.
(4 marks)
2.
(a)
Describe the fuel cell which uses hydrogen and oxygen, giving the reactions
taking place at the electrodes.
(4 marks)
(b)
Using the data booklet, calculate the emf of the cell described in (a).
(3 marks)
(c)
In the rechargeable nickel/cadmium cell, the cadmium electrode releases
electrons to the external circuit. The relevant electrode reactions are:
Cd(OH)2 + 2 e–
Cd(s) + 2 OH–(aq)
NiO(OH)(s) + H2O(l) + e–
Ni (OH) 2 (s) + OH − (aq)
Draw a cell diagram for this arrangement , showing polarity of the electrodes,
and construct a balanced equation for the reaction that occurs during this
discharge.
(3 marks)
(d)
A current was passed through 2 beakers, containing aqueous silver nitrate
solution and copper (11) solution, connected in series. After 30 min 0.10 g of
Cu was deposited.
Calculate
(i)
the mass of silver deposited
(ii)
the current used in the electrolysis.
(4 marks)
CHM 112 / Page 10 of 13
3.
Chrome yellow, the pigment used for yellow road markings, is lead (II) chromate (VI),
Pb Cr O4.
(a)
Write an equation, with state symbols, for the formation by precipitation of
PbCrO4.
(2 marks)
(b)
The solubility product of PbCrO4 at 15 °C is 1.69 x 10-14 mol² dm-6.
(i)
(ii)
(iii)
(c)
Write an expression for the solubility product, Ksp, of PbCrO4.
(2 marks)
What is the solubility, in mol dm-3, of PbCrO4?
(2 marks)
Concentrated aqueous lead (II) nitrate is added dropwise to
0.010 mol dm-3 potassium chromate (VI). What is the concentration, in
mol dm-3 of lead (II) ions when the first trace of precipitate appears?
(2 marks)
Chrome yellow has been used for a long time as a yellow pigment in oil
paintings.
(i)
(ii)
Use the standard redox potentials below to explain why the yellow
colour changes when the painting is exposed to an atmosphere
containing sulphur dioxide.
SO 24 − + 4 H+ + 2e-
2 H2O + SO2
E° = +0.17V
CrO 24 − + 8H+ + 3e-
Cr3+ + 4H2O
E° = +1.33V
(2 marks)
What colour change takes place?
(2 marks)
CHM 112 / Page 11 of 13
4.
(a)
The equation for the reaction between iodine and aqueous sodium thiosulphate
is given below.
2 Na2 S2 O3 + I2 → Na2 S4 O6 + 2 NaI
Chlorine however oxidises aqueous sodium thiosulphate to sodium sulphate.
(i)
(ii)
5.
Write a balanced equation for this reaction.
(2 marks)
Suggest why sodium thiosulphate reacts differently with iodine and
chlorine.
(3 marks)
(b)
What are the products of the reaction of NaCl, NaBr, NaI with conc. H2SO4?
(5 marks)
(c)
Explain briefly why the addition of chlorine to drinking water is of great
importance.
(3 marks)
(a)
State Le Chatelier’s principle
(3 marks)
(b)
A misture of 0.50 mol of ethanoic acid and 1.00 mol of ethanol was shaken for
a long time to reach equilibrium. The whole mixture was titrated quickly with
1.00 mol dm-3 sodium hydroxide and 80 cm3 of alkali were required.
CH3 CH2 OH(l) + CH3 COOH(l)
CH3 COOCH2 CH 3( l ) + H2 O(l)
By making use of the titration results and the equation, calculate
(i)
how many moles of ethanoic acid remained at equilibrium.
(2 marks)
(ii)
(iii)
(iv)
(v)
how many moles of ethanoic acid had reacted.
(2 marks)
how many moles of ethanol were left in the equilibrium mixture.
(2 marks)
write the expression for the equilibrium constant, Kc, for the above
equation.
(2 marks)
Calculate a value for Kc for this reaction.
(2 marks)
CHM 112 / Page 12 of 13
6.
At 700 °C, nitrogen monoxide and hydrogen react as follows:
2NO(g) + 2H2(g) → N2(g) + 2H2O(g)
The results of some investigations of the rate of this reaction are shown below:
(a)
Explain what is meant by the term order of reaction.
(2 marks)
(b)
(i)
Use the below data to determine the order of the reaction with respect
to
(1)
(2)
nitrogen monoxide,
hydrogen
(1 mark)
Experiment
number
1
2
3
4
5
6
Initial
concentration
of nitrogen
monoxide
/ mol dm-3
0.0020
0.0040
0.0060
0.012
0.012
0.012
Initial
concentration
of hydrogen
Initial
rate of
reaction
/ mol dm-3
0.012
0.012
0.012
0.0020
0.0040
0.0060
/ mol dm-3 s-1
0.0033
0.013
0.030
0.020
0.040
0.060
(ii)
Use these answers to write a rate equation for the reaction. This will
include the rate constant, k.
(1 mark)
(iii)
Determine a value for k, stating the units.
(2 marks)
(c)
Explain briefly why the initial reaction rate would be expected to increase by
increasing each of the following:
(i)
(ii)
the pressure,
the temperature
(2 marks)
[Note: a different explanation is required for each of these factors.]
CHM 112 / Page 13 of 13
(d)
With the aid of a sketch of the Boltzmann distribution, explain how both an
increase in temperature and the presence of a catalyst increase the rate of a
chemical reaction.
(4 marks)
(e)
Describe and explain the trend observed in the ease of thermal decomposition
of the carbonates of the Group II elements magnesium to barium. Write
equations where appropriate.
(4 marks)
-
THE END -
Ms.Words/CHM112AUG02F/Lynn