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Q4:
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CHEMISTRY 120 (2) DR. J. F. C. TURNER
2ND EXAMINATION
MONDAY, 14TH OCTOBER, 2002
2 HOURS
ANSWER ALL QUESTIONS
YOU MAY NOT USE PROGRAMMABLE CALCULATORS, NOTE CARDS OR ANY OTHER SIMILAR WRITTEN MATERIALS
SHOW ALL YOUR WORK
NAME
1(a)
SECTION
Name the following compounds
Co2(SO4)3
Cobalt (III) sulfate
EtCl
Chloroethane or Ethyl chloride
CoSO4
Cobalt (II) sulfate
IF7
Iodine heptafluoride
10
(b)
Write down the molecular formula for each one for the eight compounds shown below
A1
C4H6O
A2
C4H8O
B1
C4H7O2Cl
B2
C4H7O2Cl
C1
C5H9Br
C2
C5H9Br
D1
C5H12
D2
C5H12
8
O
Cl
O
O
OH
OH
A
Br
O
Cl
B
Br
D
C
B and C are isomers, A and D are not
(c)
By looking at the structure, determine which pairs are isomers. For each isomeric pair, put a
check in the box. For those that are not isomers, put a cross in the box
4
(d)
Write the formula for the compounds named below:
Magnesium Oxide
MgO
Beryllium Fluoride
Ammonium Nitrate
NH4NO3
Copper (II) Oxide
BeF2
CuO
4
(g)
Balance the following equations:
Fe + Cl2
FeCl3
C 3H 6 + O 2
CO2 + H2O
2Fe + 3Cl2
2FeCl3
C 3H6 + 9/ 2O2
3CO2 + 3H2O
Fractional constants or whole numbers are OK
7
33
2(a)
Write down the relationship between pressure, (P), volume, (V), temperature, (T) and quantity of
gas, (n), assuming that the gas is ideal or perfect
PV = nRT
2
(b)
A.
Write down three assumptions for perfect gas behavior.
From:
No forces between particles
B
Zero particle size
C
Elastic collisions
Straight line trajectories
6
(c)
Is it possible to liquefy a perfect gas? Why or why not?
No – no forces between particles
4
(d)
Standard temperature and pressure is defined as 0oC and 1 atmosphere pressure. What is the
volume of 1 mole of a perfect gas under these conditions?
22.4 L
1
(e)
What is the volume of a perfect gas at room temperature (298 K) and 1 atmosphere pressure?
24 L
1
(f)
Half a mole of a perfect gas at a temperature T and 1 atmosphere pressure is found occupy
18.46L. What is the temperature T in K or oC?
PV = nRT
=> T = PV/nR
P = 1 atm = 101,325 Pa
V = 18.46 L = 18.46 x 10-3 m3
n = 0.5 mol
T = (101325 x 18.46 x 10-3)/0.5 x 8.314 = 450 K or 176.85 oC
4
(g)
Calculate the pressure, in atmospheres, of a mole of a perfect gas at a temperature of 350 K in a
flask of volume 30ml
PV = nRT
=> P = nRT/V
T = 350 K
V = 30 mL = 30 x 10-6 m3
n = 1 mol
P = (1 x 8.314 x 350 )/ 30 x 10-6 = 96,996,667 Pa = 957 atm
4
(h)
The gas sample in (g) is cooled to 150 K. What is the pressure at this new temperature?
PV = nRT
=> P = nRT/V
T = 150 K
V = 30 mL = 30 x 10-6 m3
n = 1 mol
P = (1 x 8.314 x 150 )/ 30 x 10-6 = 41,570,000 Pa = 410 atm
4
(i)
What volume, in mL, is required to contain 0.01 mole of a perfect gas at a temperature of 200 K
so that the pressure is 0.5 atmospheres?
PV = nRT
=> V = nRT/P
T = 200 K
P = 0.5 atm = 50662.5 Pa
n = 0.01 mol
V = (0.01 x 8.314 x 200 )/ 50662.5 = 328.2 mL
4
(j)
2.8 g of nitrogen gas is held at 500 K at a pressure of 10 atmospheres. What is the density of the
gas at this temperature in gL-1? Need to calculate V as ρ = m/V
PV = nRT
=> V = nRT/P
T = 500 K
P = 10 atm = 50662.5 Pa
n = 2.8/28 = 0.1 mol
V = (0.1 x 8.314 x 500 )/ 101325 x 10 = 0.41 L
ρ = 2.8/0.41 = 6.82 gL-1
[RAM of N = 14 gmol-1R = 8.314 JmolK-1 or ]
4
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3(a)
Draw the structural formula for cyclohexane, C6H12
H2
C
CH2
CH2
CH2
CH2
or
C6H12
C
H2
2
(b)
Combustion of cyclohexane in oxygen produces only carbon dioxide and water. Write a balanced
equation for this reaction.
C6H12(l)+ 9O2(g)
6CO2(g) + 6H2O(l)
8
(c)
When 0.105 mol cyclohexane is burned in excess oxygen, how many moles of oxygen are
consumed?
9 x 0.105 = 0.945 mol
6
(d)
In a combustion experiment at 600 K, at which temperature cyclohexane is a gas and behaves as
a perfect gas, 12 moles of O2 and 0.5 moles of cyclohexane are contained in a flask of volume 50 L.
Calculate the total pressure in the vessel in atmospheres.
PV = nRT
=> P = nRT/V
T = 600 K
V = 50 L = 50 x 10-3 m3
n = 12.5 mol
P = (12.5 x 8.314 x 600)/ 50 x 10-3 = 1,247,100 Pa = 12.3 atm
6
(e)
What molecular species are present after the combustion is complete in this system?
O2, H2O and CO2
3
(f)
How many moles of each species are present?
n(CO2) = 0.5 x 6 = 3 mol
n(H2O) = 0.5 x 6 = 3 mol
n(O2) = 12 - 4.5 = 7.5 mol
6
(g)
What is the final pressure in the flask, assuming that the temperature and the volume are the
same. Also assume that, at 600 K, water behaves as a perfect gas.
PV = nRT
=> P = nRT/V
T = 600 K
V = 50 L = 50 x 10-3 m3
n = 3 + 3 + 7.5 = 13.5 mol
P = (13.5 x 8.314 x 600)/ 50 x 10-3 = 13.284 atm
(or P = (12.3/12.5) x 13.5 = 13.284 atm
8
(h)
What are the partial pressures in the flask before and after the reaction?
Before: n(O2) = 12 mol => P(O2) = 12/12.5 x 12.3 = 11.808 atm
Before: n(C6H12) = 0.5 mol => P(C6H12) = 0.5/12.5 x 12.3 = 0.492 atm
After: n(O2) = 7.5 mol => P(O2) = 7.5/13.5 x 13.284 = 7.38 atm
After: n(CO2) = 3 mol => P(CO2) = 3/13.5 x 13.284 = 2.952 atm
After: n(H2O) = 3 mol => P(CO2) = 3/13.5 x 13.284 = 2.952 atm
8
47
4(a)
Aluminum metal, when reacted with titanium tetrachloride at high temperature, forms aluminum
chloride and titanium metal. Write a balanced chemical equation for this reaction. Do not include the
states for this reaction.
4AlCl3 + 3Ti
4Al + 3TiCl4
6
(b)
What mass of aluminum is required to convert 9.5 g of titanium tetrachloride to titanium metal?
RMM for TiCl4 = 48 + 4 x 35.5 = 190 gmol-1
9.5 g = 9.5/190 = 0.05 mol
stoichiometric ratio = 3:4 => (0.05/3) x 4 = 0.067 mol Al = 1.809 g
(c)
[RAM Ti = 48 gmol-1; Cl = 35.5 gmol-1; Al = 27 gmol-1]
Is this reaction a redox reaction?
Yes
(d)
Write the half reactions for Al and Ti in this reaction
6
2
Al - 3e-
Ti - 4e-
Al3+
or
or
Ti
Al3+ + 3e-
Al
Ti4+
Ti4+ + 4e8
(e)
VO43-
Write down the oxidation state of the atom in the following species in bold:
SO42BF4-
NiI2
V(V)
O(-II)
B(III)
Ni(II)
P4
NaMnO4
ClO-
ClO4-
P(0)
Mn(VII)
Cl(I)
Cl(VII)
8
(f)
For each element in bold, write the oxidation state on either side of the equation in the box
provided.
Ga2O3 + 2Al
III
0
Mg(s) + Cu2+(aq)
0
II
CH4 + 2O2
-IV
0
2Ga + Al2O3
0
III
Mg2+(aq) + Cu(s)
II
0
CO2 + 2H2O
IV
-II
12
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5(a)
A portion of the Periodic Table is shown below. Some of the elements are missing. Fill in the
missing symbols of these elements, together with their atomic numbers.
= empty element place
H
He
1
2
Li
Be
B
C
5
6
Al
Si
N
O
F
Ne
P
S
Cl
Ar
15
16
2
3
Na
Mg
3
11
K
Ca
Sc
Ti
21
22
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
29
30
18
4
s block
d block
p block
24
(b)
Write the names of each block in the boxes below the table.
3
(c)
Which of the following acids are strong?
Write S for strong and W for weak in the boxes.
Acid
HBr
CH3CO2H
H2SO4
HCl
NH4+
H3PO4
HNO3
HClO4
Strength
S
W
S
S
W
W
S
S
(d)
Which of the following bases are strong?
Write S for strong and W for weak in the boxes.
8
Base
MeNH2
LiOH
NH3
ClIBa(OH)2
Me2NH
KOH
Strength
W
S
W
W
W
S
W
S
8
43
The End