CONFIDENTIAL DK 035
Chemistry
Semester
III
2012/2013
1
hour
KOLEJ MATRIKULASI SELANGOR
KEMENTERIAN PELAJARAN MALAYSIA
PRA UPS III
SEMESTER
III
TWO
YEAR PROGRAMME
SESSION
2012/2013
CHEMISTRY
DK 035
Answers all FOUR (4) questions
TABLE
OF RELATIVE ATOMIC MASSES
Element
|
Symbol
|
Proton number
|
Relative atomic mass
|
|
Aluminum
|
Al
|
13
|
26.98
|
|
Antimony
|
Sb
|
51
|
121.76
|
|
Argon
|
Ar
|
18
|
39.95
|
|
Arsenic
|
As
|
33
|
74.92
|
|
Barium
|
Ba
|
56
|
137.33
|
|
Beryllium
|
Be
|
4
|
9.01
|
|
Bismuth
|
Bi
|
83
|
208.98
|
|
Boron
|
B
|
5
|
10.81
|
|
Bromine
|
Br
|
35
|
79.90
|
|
Cadmium
|
Cd
|
48
|
112.41
|
|
Calcium
|
Ca
|
20
|
40.08
|
|
Carbon
|
C
|
6
|
12.01
|
|
Cerium
|
Ce
|
58
|
140.12
|
|
Cesium
|
Cs
|
55
|
132.91
|
|
Chlorine
|
Cl
|
17
|
35.45
|
|
Chromium
|
Cr
|
24
|
52.00
|
|
Cobalt
|
Co
|
27
|
58.93
|
|
Copper
|
Cu
|
29
|
63.55
|
|
Fluorine
|
F
|
9
|
19.00
|
|
Gold
|
Au
|
79
|
197.00
|
|
Helium
|
He
|
2
|
4.00
|
|
Hydrogen
|
H
|
1
|
1.01
|
|
Iodine
|
I
|
53
|
126.90
|
|
Iron
|
Fe
|
26
|
55.85
|
|
Krypton
|
Kr
|
36
|
83.80
|
|
Lead
|
Pb
|
82
|
207.20
|
|
Lithium
|
Li
|
3
|
6.94
|
|
Magnesium
|
Mg
|
12
|
24.31
|
|
Manganese
|
Mn
|
25
|
54.94
|
|
Mercury
|
Hg
|
80
|
200.59
|
|
Neon
|
Ne
|
10
|
20.18
|
|
Nickel
|
Ni
|
28
|
58.69
|
|
Nitrogen
|
N
|
7
|
14.01
|
|
Oxygen
|
O
|
8
|
16.00
|
|
Phosphorus
|
P
|
15
|
30.97
|
|
Platinum
|
Pt
|
78
|
195.08
|
|
Potassium
|
K
|
19
|
39.10
|
|
Protactinium
|
Pa
|
91
|
231.04
|
|
Radium
|
Ra
|
88
|
226.03
|
|
Radon
|
Rn
|
86
|
222.02
|
|
Rubidium
|
Rb
|
37
|
85.47
|
|
Scandium
|
Sc
|
21
|
44.96
|
|
Selenium
|
Se
|
34
|
78.96
|
|
Silicon
|
Si
|
14
|
28.09
|
|
Silver
|
Ag
|
47
|
107.87
|
|
Sodium
|
Na
|
11
|
22.99
|
|
Strontium
|
Sr
|
38
|
87.62
|
|
Sulphur
|
S
|
16
|
32.07
|
|
Tin
|
Sn
|
50
|
118.71
|
|
Tungsten
|
W
|
74
|
183.84
|
|
Uranium
|
U
|
92
|
238.03
|
|
Zinc
|
Zn
|
30
|
65.39
|
|
LIST OF SELECTED CONSTANT VALUES
Ionization constant for water at 25°C Kw = 1.0 ´ 10-14 mol2
dm-6
Molar volume of gases Vm = 22.4 dm3 mol-1 at STP
= 24 dm3 mol-1 at room
condition (25 °C, 1 atm)
Speed of light in a vacuum c =
3.0 ´ 108 m s-1
Specific
heat of water = 4.18 kJ kg-1 K-1
= 4.18 J g-1 K-1
= 4.18 J g-1 °C-1
Avogadro’s
number NA = 6.02´1023
mol-1
Faraday constant F = 96500 C mol-1
Planck constant h = 6.63´10-34 J s
= 6.63´10-34 Kg m2
s-1
Rydberg constant RH = 1.097 ´ 107 m-1
= 2.18 ´ 10-18 J
Ideal gas constant R = 8.314 m3 Pa mol-1 K-1
= 8.314 J mol-1 K-1
= 0.08206 L atm mol-1 K-1
= 62.36 L mmHg mol-1 K-1
Density of water at 25°C =
1 g cm-3
Freezing
point of water
= 0.00 °C
= 273.15 K
Vapour
pressure of water at 25°C Pwater = 23.76 torr
1.
UNIT AND
CONVERSION FACTOR
VOLUME 1 L = 1
dm3
1mL = 1
cm3
ENERGY 1 J = 1 kg m2 s-2 = 1 N m = 1 ´ 107
erg
1 calorie = 4.184
J
1eV molecule-1 = 96.7 kJ mol-1
PRESSURE 1 atm = 760 mmHg = 760 torr =101 325 Pa =101 325 N m-2
TEMPERATURE 0°C =
273.15 K
OTHERS 1 faraday (F) = 96 500 C
1 newton (N) = 1 kg m s-2
Answers
all FOUR (4) questions
1 a. Define
i. Open system
[ 1 mark ]
ii. Differentiate between endothermic and
exothermic reactions.
[4 marks]
b. A
0.1375 g sample of solid magnesium is burned in a constant-volume bomb
calorimeter that has a heat capacity of 1769 J oC-1. The
calorimeter contains exactly 300 g of water, and the temperature increases by
1.126 oC. Calculate the heat of combustion for Magnesium in kJ mol-1.
[ Specific Heat Capacity of water = 4.18 J g-1
oC-1 ]
[
5 marks ]
2 a) By
using data below, construct an appropriate energy cycle diagram to show
the dissolution process
of sodium hydroxide, NaOH and calculate enthalpy of
hydration of OH-.
∆H
(kj mol-1)
|
|
Enthalpy of hydration
of Na+
|
-410
|
Enthalpy of solution
of NaOH
|
-44.5
|
Lattice energy of
NaOH
|
-900
|
[5 marks]
b)
The
Born-Haber cycle for magnesium chloride, MgCl2 is as shown below:
Enthalpy
Mg2+ (g)
+ 2e + 2Cl (g)
Bond dissociation DH4 = +243 kJ
DH5 = –368 kJ
energy
C Mg2+ (g) + 2Cl- (g)
Second Ionization
energy of Mg DH3 =
+1450 kJ
Mg+ (g) + e
+ Cl2 (g)
DH6 = U kJ
DH2 = +736 kJ
Mg (g) + Cl2 (g)
DH1 = +151 kJ
Mg (s) + Cl2 (g)
DH7
= –645 kJ
MgCl2 (s)
Name
the enthalpies labeled ∆H2 and ∆H5. Write the equation for reaction C. Calculate
the lattice energy for MgCl2.
[5 marks]
3. a) A galvanic
cell consist of a silver cathode immersed in a 0.15 M solution of
AgNO3 and a platinum anode that has gaseous hydrogen
bubbling over it at a pressure of 1.0 atm. The hydrogen ion concentration of
the solution is 0.02 M.
Based on the data given, draw and labeled the cell diagram to
represent the above galvanic cell.
[
6 Marks ]
b) An
electrochemical cell is set up using copper and silver half-cells.
Cu(s)| Cu2+(aq)
|| Ag+(aq) | Ag(s)
i.
What is the overall cell reaction?
ii.
Calculate the cell potential under standard
condition
iii.
The cell potential is 0.45V when the
concentrations of copper(II) ion and silver ion are x M and 0.70 M respectively.
What is
the value for x?
[
4 Marks ]
E0cell Cu2+ | Cu(s) = 0.34 V Ag+(aq) | Ag(s) = 0.80 V
4 a) Predict
the products of the electrolysis of concentrated aqueous solution of sodium
chloride in a cell using graphite electrodes. Give reasons.
[4 marks]
b) In
electrolysis of molten chromium(III) chloride, CrCl3 using graphite
electrodes, calculate the time (in minutes) required to obtain 3.24 g of
chromium using a current of 10.0 A.
[6 marks]
End
of question paper
NO
|
PART
|
ANSWERS
|
||||||||||||||||||||||||||||
1
|
(a) i
|
Open
system is a system that allowed the
exchange of mass and energy
from the system to its surrounding
|
||||||||||||||||||||||||||||
ii
|
|
|||||||||||||||||||||||||||||
b
|
q
= mwcw∆T +
Cc∆T @
= (300g)(4.18 Jg-1oC-1)(1.126oC) +
(1769 JoC-1)(1.126oC)
= 3403.898
J @ 3.4039 kJ
=
5.6584 x
10-3 mole
 5.6584 x
10-3 mole Mg ≡ 3.4039 kJ
1.0 mole
Mg ≡ 601.57 kJ
The enthalpy of Mg is 601.57
kJ/mol
|
2
|
(a)
|
∆Hsoln = -∆Hlattice + ∆Hhyd of Na+ + ∆Hhyd of OH-
@
- 44.5
= -(-900) + (-410) + ∆Hhyd
of OH-
∆Hhyd of OH- = -534.5 kj mol-1
|
(b)
|
∆H2
= First Ionisation Energy of Mg and
∆H5
= Electron affinity of Cl
Equation
for reaction C :
Mg2+ (g) + 2e + Cl2 (g)
DH7 = DH1
+DH2 +DH3 +DH4 +DH5
+DH6
@
–645
kJ = +151 kJ + +736 kJ
+1450 kJ +243 kJ + (–368 kJ) + DH6
DH6 = -2857 kJmol-1 (lattice
energy of MgCl2)
|
3
|
a
|
||||||||||||
bi.
|
 Cu(s) +
2Ag+(aq) Cu2+(aq) +
2Ag(s) |
||||||||||||
bii.
|
Eocell =
Eocathode
- Eoanode
= + 0.80 V – (+0.34 V)
=
+ 0.46 V
|
||||||||||||
biii.
|
@
x =
1.1 M
|
4
|
(a)
|
At
cathode:
Hydrogen gas is produced
@
2H2O(l) + 2e- à H2(g) + 2OH-(aq)
Reason:
Eo for water
molecules is more positive
@
H2O is easier
to be reduced than Na+
At
anode:
Chlorine gas is
produced.
@
2Cl- (aq) à Cl2(g) + 2e-
Reason:
Because of high
concentration of Cl-
|
(b)
|
Cr3+(l) + 3e- à Cr(s)
Number of mole of Cr =
 = 0.0623
mol
1 mol Cr º 3
mole of e- º 3
F º 3 x 96500 C
0.0623 mol Cr º 0.0623 mol x 3 x 96500 C @
= 18035.85 C
Q = I x t
18035.85 C = 10.0 t
t
= 30 minutes
|
End
of Answers
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