UNIVERSITY OF NATAL DURBAN
EXAMINATION : JUNE 2003
CHEMISTRY 1 (a) – DSC 1EN1
Duration:
1½ Hours
Total Marks: 100
INTERNAL EXAMINER
:
Dr H G Kruger
EXTERNAL EXAMINER
:
Dr D Jaganyi
University of Pietermaritzburg
IMPORTANT : COMPLETE THIS SECTION IMMEDIATELY
SURNAME AND INITIAL (optional) ____________________________________
STUDENT NUMBER: ____________________ SEAT NUMBER: __________
SIGNATURE:_________________________________________________________
This paper consists of 16 pages including a Periodic Table. Please ensure that you have
them all.
QUESTION
1 (30)
2 (30)
3 (40)
TOTAL (100)
INTERNAL
EXTERNAL
FINAL
R = 8.314 JK-1 mol-1 = 0.0821 L atm K-1 mol-1 = 62.4 L Torr K-1 mol-1
1 atm = 101.325 kPa
Vap. Press. of H2O at 26.0oC = 25 Torr.
PLEASE USE THE INFORMATION TECHNOLOGY
DIVISION MCQ ANSWER SHEET FOR QUESTION 1
UNIVERSITY OF NATAL DURBAN
EXAMINATION : JUNE 2003
CHEMISTRY 1 (a) – DSC 1EN1
Page 2
QUESTION 1
PLEASE USE THE INFORMATION TECHNOLOGY
DIVISION MCQ ANSWER SHEET FOR QUESTION 1
MULTIPLE CHOICE: . CHOOSE THE ONE ALTERNATIVE THAT BEST
COMPLETES THE STATEMENT OR ANSWERS THE QUESTION.
1.1
A stock solution of HNO3 is prepared and found to contain 13.5 M of HNO3. If
25.0 mL of the stock solution is diluted to a final volume of 0.500 L, the
concentration of the diluted solution is ____________ M.
(a)
0.270
(b)
1.48
(c)
0.675
(d)
675
(e)
270
(2)
1.2
Pure acetic acid (HC2COOH) is a liquid and is known as glacial acetic acid.
Calculate the molarity of a solution prepared by dissolving 10.00 mL of glacial
acetic acid at 25oC in sufficient water to give 500.0 mL of solution. The density
of glacial acetic acid at 25oC is 1.049 g/mL.
(a) 1.26 x 103
(b)
21.0
(c)
0.0210 (d)
0.350
(e) 3.50 x 10-4
(2)
1.3
Silver ions can be precipated from aqueous solutions by the addition of aqueous
chloride:
Ag+ (aq) + Cl− (aq) → AgCl (s)
Silver chloride is virtually insoluble in water so that the reaction appears to go to
completion. How many grams of solid NaCl must be added to 25.0 mL of 0.366
M AgNO3 solution to completely precipitate the silver?
(a) 9.15 x 10-3
(b) 1.57 x 10-4
(c)
0.535
(d)
0.157
(e) 6.39 x 103
(2)
UNIVERSITY OF NATAL DURBAN
EXAMINATION : JUNE 2003
CHEMISTRY 1 (a) – DSC 1EN1
Page 3
QUESTION 1 (continued)
1.4
A solution is prepared by adding 1.60 g of solid NaCl to 50.0 mL of 0.100 M
CaCl2. What is the molarity of chloride ion in the final solution? Assume that the
volume of the final solution is 50.0 mL.
(a)
0.747
(b)
0.647
(c)
0.132
(d)
0.232
(e)
0.547
(2)
1.5
The molecular weight of urea (NH2)2CO), a compound used as a nitrogen
fertilizer, is ________________ amu.
(a)
44.0
(b)
43.0
(c)
60.1
(d)
8.0
(e)
32.0
(2)
1.6
What is the empirical formula of a compound that is 64.8% C, 13.6% H, and
21.6% O by mass?
(a) C4HO1
(b) C5HO2
(c) C8H20O2
(d) C5H14O1
(e) C4H10O1
(2)
1.7
Lithium and nitrogen react in a combination reaction to produce lithium nitride:
6Li (s) + N2 (g) → 2Li3N (s)
How many moles of N2 are needed to react with 0.500 mol of lithium?
(a)
3.00
(b)
0.500
(c)
0.167
(d)
1.50
(e)
0.0833
(2)
UNIVERSITY OF NATAL DURBAN
EXAMINATION : JUNE 2003
CHEMISTRY 1 (a) – DSC 1EN1
Page 4
QUESTION 1 (continued)
1.8
Automotive air bags inflate when sodium azide decomposes explosively to its
constituent elements:
2NaN3 (s) → 2Na (s) + 3N2 (g)
How many moles of N2 are produced by the decomposition of 2.88 mol of sodium
azide?
(a)
1.92
(b)
8.64
(c)
4.32
(d)
0.960
(e)
1.44
(2)
1.9
Calcium hydride (CaH2) reacts with water to form hydrogen gas:
CaH2 (s) + 2H2O (l) → Ca(OH)2 (aq) + 2H2 (g)
How many grams of CaH2 are needed to generate 48.0 L of H2 gas at a pressure of
0.888 atm and a temperature of 32oC?
(a)
50.7
(b)
0.851
(c)
143
(d)
35.8
(e)
71.7
(2)
1.10
Zinc reacts with a aqueous sulphuric acid to form hydrogen gas:
Zn (s) + H2SO4 (aq) → ZnSO4 (aq) + H2 (g)
In an experiment, 225 mL of wet H2 is collected over water at 27oC and a
barometric pressure of 748 torr. How many grams of Zn have been consumed?
The vapor pressure of water at 27oC is 26.74 torr.
(a) 4.79 x 106
(b)
0.567
(c)
567
(d)
431
(e) 4.31 x 105
(2)
UNIVERSITY OF NATAL DURBAN
EXAMINATION : JUNE 2003
CHEMISTRY 1 (a) – DSC 1EN1
Page 5
QUESTION 1 (continued)
1.11
The kinetic energy of a 7.3 kg steel ball travelling at 18.0 m/s ______________ J.
(a) 1.2 x 103
(b)
66
(c) 2.4 x 103
(d)1.3 x 102
(e)
7.3
(2)
1.12
Which one of the following statements is false?
(a)
(b)
(c)
(d)
(e)
E is a state function.
The actual numerical value of E can be measured.
∆E = Efinal − Einitial
∆E = q + w
When a system undergoes a process in which it gains energy from the
surroundings, the ∆E for the process is positive.
(2)
1.13
The value of ∆E for a system that performs 213 kJ of work on its surroundings
and loses 79 kJ of heat is _____________ kJ.
(a)
+292
(b)
-292
(c)
+134
(d)
-134
(e)
-213
(2)
1.14
Which one of the following is an exothermic process?
(a)
(b)
(c)
(d)
(e)
1.15
ice melting
water evaporating
boiling soup
condensation of water vapor
Ammonium thiocyanate and barium hydroxide are mixed at 25oC: the
temperature drops.
(2)
o
The value of ∆H for the reaction below is –72 kJ. How many kJ of heat is
released when 1.0 mol of HBr is formed in this reaction?
H2(g) + Br2(g) → 2HBr(g)
(a)
144
(b)
72
(c)
0.44
(d)
36
(e)
-72
(2)
[30]
UNIVERSITY OF NATAL DURBAN
EXAMINATION : JUNE 2003
CHEMISTRY 1 (a) – DSC 1EN1
Page 6
QUESTION 2
2.1
2.2
How many grams of Ca(OH)2 are needed to neutralize 25.0 mL of 0.100 M
HNO3?
(3)
A sample of 70.5 mg of potassium phosphate is added to 15.0 mL of 0.050 M
silver nitrate, resulting in the formation of a precipitate. The equation for the
reaction is:
K3PO4(ag) + 3 AgNO3 → Ag3PO4(s) + 3 KNO3(aq)
(a)
What is the limiting reagent in the reaction?
(b)
Calculate the theoretical yield, in grams, of the precipitate that forms.
(4)
(4)
UNIVERSITY OF NATAL DURBAN
EXAMINATION : JUNE 2003
CHEMISTRY 1 (a) – DSC 1EN1
Page 7
QUESTION 2 (continued)
2.3
H2 and O2 are mixed in a closed cylinder and then ignited. As the reaction occurs,
the system loses 1150 J of heat to the surroundings. The reaction also causes the
piston of the cylinder to rise due to an increase in volume. The rising piston does
480 J of work on the surroundings as it pushes a flying wheel. What is the change
in the internal energy of the system?
(2)
UNIVERSITY OF NATAL DURBAN
EXAMINATION : JUNE 2003
CHEMISTRY 1 (a) – DSC 1EN1
Page 8
QUESTION 2 (continued)
2.4
Suppose we confine 1 g of butane and sufficient oxygen to completely combust it
in a cylinder as above. The cylinder, however, is perfectly insulating, so that no
heat can escape to the surroundings. A spark initiates combustion of the butane
and CO2 and H2O form. If we use this cylinder to measure the enthalpy change in
the reaction, would the piston rise, fall, or stay the same? Motivate your answer.
HINT: 2C4H10(g) + 13 O2(g) → 8 CO2(g) + 10 H2O(g)
2.5
(3)
How much heat is released when 4.5 g of methane gas is burned in a constantpressure system?
CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) ∆H = −890 kJ
(3)
UNIVERSITY OF NATAL DURBAN
EXAMINATION : JUNE 2003
CHEMISTRY 1 (a) – DSC 1EN1
Page 9
QUESTION 2 (continued)
2.6
Propane is combusted in presence of oxygen to form CO2 and H2O. Apply Hess’s
law on the following heats of formations to calculate the standard enthalpy change
for the reaction where propane is burned in oxygen under standard conditions:
C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(l)
3 C(s) + 4H2(g) → C3H8(g)
C(s) + O2(g) → CO2(g)
H2O(l) → ½H2(g) + ½O2(g)
∆H = −103.85 kJ
∆H = −393.5 kJ
∆H = 285.8 kJ
(6)
2.7
Describe the process of converting Pyrite (FeS2) to sulfuric acid.
(5)
[30]
UNIVERSITY OF NATAL DURBAN
EXAMINATION : JUNE 2003
CHEMISTRY 1 (a) – DSC 1EN1
Page 10
QUESTION 3
3.1
Write down a balanced reaction for Marble with hydrochloric acid. Indicate the
phase of each molecule.
(2)
3.2
Write down the approximate composition of gun metal?
(2)
UNIVERSITY OF NATAL DURBAN
EXAMINATION : JUNE 2003
CHEMISTRY 1 (a) – DSC 1EN1
Page 11
QUESTION 3 (continued)
3.3
Use the electronegativity of the elements (given in brackets) to discuss the
polarity of the LiH bond. Indicate the charges of each atom (use δ+ or δ− only).
Li (1.0) and H (2.1).
(3)
3.4
Complete the following reactions (give an indication of the state of the products
eg colour, solubility, gas, solid etc):
H2SO4(aq) + R−NH2(l) →
NH3(g) + HCl(g) →
(2)
(2)
UNIVERSITY OF NATAL DURBAN
EXAMINATION : JUNE 2003
CHEMISTRY 1 (a) – DSC 1EN1
Page 12
QUESTION 3 (continued)
Ca(OCl)2(g) + HCl(aq) →
Mg2+(aq) + NH4OH(aq) →
Ca2+(aq) + C2O42−(aq) →
Ba2+(aq) + H2S(g) →
Ca2+(aq) + NH4OH(aq) →
(2)
(2)
(2)
(2)
(2)
UNIVERSITY OF NATAL DURBAN
EXAMINATION : JUNE 2003
CHEMISTRY 1 (a) – DSC 1EN1
Page 13
QUESTION 3 (continued)
Ca2+(aq) + NAOH (conc) →
(2)
Pb2+(aq) + NH4OH(aq) →
3.5
(2)
Name 2 of the 4 main cement clinkers (give the approximate chemical
composition as well as the industrial abbreviation).
(4)
UNIVERSITY OF NATAL DURBAN
EXAMINATION : JUNE 2003
CHEMISTRY 1 (a) – DSC 1EN1
Page 14
QUESTION 3 (continued)
3.6
Explain how Germanium can be “doped” with Arsenic to produce a n-type semi
conductor. (Give a 2-dimensional structure of the resulting crystal matrix).
(5)
3.7
Define a primary explosive and give an example.
(2)
UNIVERSITY OF NATAL DURBAN
EXAMINATION : JUNE 2003
CHEMISTRY 1 (a) – DSC 1EN1
Page 15
QUESTION 3 (continued)
3.8
Discuss the rocket fuel used for the American space shuttles. (Give appropriate
reactions).
(4)
[40]