Sample Final Examination Chemistry 217

Sample Final Examination Chemistry 217
Multiple-choice Questions (2 marks each)
Circle the appropriate response.
1. A sky-blue aqueous solution was labeled "chromium(II) perchlorate". This solution
contains the ions
A) Cr2O2+ and ClO4–.
B) Cr2O4+ and Cl–.
C) Cr2+ and Cl–.
D) Cr2+ and ClO4–.
E) Cr3+ and ClO4–.
2. A green compound composed of chromium and oxygen contains 68.42% Cr. What is the
empirical formula of the compound?
A) Cr3O
B) Cr2O3
C) CrO3
D) Cr2O
E) Cr2O2
3.
A)
B)
C)
D)
E)
The F–F bond length in F2(g) is 1.42 Å. If 1 Å = 10–10 m, what is the bond length in pm?
14.2 pm
71 pm
1420 pm
142 pm
0.142 pm
4. If an aqueous solution of sulfuric acid is added to a pool of mercury, SO2(aq) and
mercury(II) sulfate are formed. Which species is reduced?
A) H2SO4(aq)
B) Hg(l)
C) H2O(l)
D) SO2(aq)
E) HgSO4(aq)
5.
A)
B)
C)
D)
E)
When BaO(s) dissolves in water,
the resulting solution is acidic.
hydrogen gas is produced.
O2–(aq) reacts with water to give hydroxide ions.
the resulting solution is neutral.
oxygen gas is produced.
6. Consider the following reactions.
ZrC(s) + 4Cl2(g) ® ZrCl4(g) + CCl4(g)
ZrCl4(g) + 2Mg(s) ® Zr(s) + 2MgCl2(l)
How many moles of Zr(s) are produced from 9.00 moles of chlorine gas?
A) 2.25 mol
B) 1.00 mol
C) 0.444 mol
D) 9.00 mol
E) 2.00 mol
7. How many moles of sodium sulfate must be added to an aqueous solution that contains
2.0 moles of barium chloride in order to precipitate 2.0 moles of barium sulfate?
A) 1.0 mol
B) 2.0 mol
C) Not enough barium chloride is available to precipitate 2.0 moles of barium sulfate.
D) 3.0 mol
E) 1.5 mol
8. Consider the following reaction.
4NH4ClO4(s) ® 2Cl2(g) + 8H2O(g) + 2N2O(g) + 3O2(g)
Calculate the total volume of all gases produced at STP by the decomposition of 5.50
moles of ammonium perchlorate.
A) 20.6 L
B) 14.7 L
C) 123 L
D) 462 L
E) 8.21 L
9. The pressure of a gas in a rigid container at 18oC is 745 Torr. What is the pressure of the
gas at –75oC?
A) 285 Torr
B) 1100 Torr
C) 760 Torr
D) 77.3 Torr
E) 507 Torr
10. Calculate the reaction enthalpy for
2S(s) + 3O2(g) ® 2SO3(g)
from the data
SO3(g) ® S(s) + 3/2O2(g)
A) +791.4 kJ
B) –395.7 kJ
C) –197.9 kJ
D) +395.7 kJ
E) –791.4 kJ
DHo = +395.7 kJ
11. If 100 mL of 1.00 M silver nitrate are added to 100 mL of 1.00 M potassium iodide in a
calorimeter with a heat capacity of 2.30 kJ/K, the temperature rises 4.87 K. Calculate the
enthalpy change for
Ag+(aq) + I–(aq) ® AgI(s)
A) –9.45 kJ
B) –4.72 kJ
C) –21.2 kJ
D) –56.0 kJ
E) –112 kJ
12.
A)
B)
C)
D)
E)
Which of the following represents the first electron affinity of oxygen?
O(g) + 2e–(g) ® O2–(g)
O(g) + e–(g) ® O–(g)
O(g) ® O+(g) + e–(g)
O(s) + e–(g) ® O–(g)
O(s) + 2e– ® O2–(g)
13.
A)
B)
C)
D)
E)
What is the valence-electron configuration of the alkaline earth elements?
np2
ns2
np1
ns1
ns2np1
14. Calculate the energy per photon of radio waves of frequency 92.1 MHz. Planck's constant
is 6.63 ´ 10–34 J · s.
A) 0.0368 J
B) 6.11 ´ 10–26 J
C) 7.20 ´ 10–42 J
D) 1.83 ´ 10–17 J
E) 1.39 ´ 1041 J
15. How many lone pairs of electrons does the iodide atom possess in the Lewis structure of
HI?
A) 3
B) 2
C) 1
D) 6
E) 4
16.
A)
B)
C)
D)
E)
How many lone pairs are there in the Lewis structure of dinitrogen tetroxide, O2N–NO2?
10
12
8
4
14
17.
A)
B)
C)
D)
E)
How many valence electrons are there in the carbonate ion, CO32–?
24
26
22
18
20
18.
A)
B)
C)
D)
E)
What type of orbitals are used to form the N–N bond in hydrazine, N2H4?
sp3–sp3
sp–sp
sp–sp3
sp–sp2
sp2–sp2
19.
A)
B)
C)
D)
E)
The O–N–O bond angle in NO3– is
equal to 90o or 180o.
<109o.
equal to 90o or 120o.
equal to 120o.
much less than 120o.
20. Consider the following:
(1) C2H4; (2) C2H2; (3) C6H6
List the carbon-carbon bonds in order of decreasing average bond enthalpy.
A) (2) > (3) > (1)
B) (1) > (2) > (3)
C) (3) > (1) > (2)
D) (3) > (2) > (1)
E) (2) > (1) > (3)
21.
A)
B)
C)
D)
E)
In which of the following would the boiling point of water be lowest?
in New York city where the pressure is about 760 Torr
in a pressure cooker where the pressure is 1400 Torr
in the "mile high" city of Denver
in New Mexico where the pressure is about 710 Torr
at the peak of Mt. Everest
22. The phase diagram for a pure substance is given below.
A)
B)
C)
D)
E)
The substance is stored in a container at 150 atm at 25oC. Describe what happens if the
container is opened at 25oC.
The liquid in the container vaporizes.
The solid in the container sublimes.
The liquid in the container freezes.
The solid in the container melts.
The vapor in the container escapes.
23. List the following in order of increasing boiling point:
hydrogen chloride, hydrogen fluoride, argon
A) HF < Ar < HCl
B) Ar < HCl < HF
C) Ar < HF < HCl
D) HCl < Ar < HF
E) HF < HCl < Ar
24. Calculate the freezing point of a 7.0 m aqueous solution of ethylene glycol. The kf for
water is 1.86 K · kg · mol–1.
A) –13oC
B) –3.8oC
C) –26oC
D) 0oC
E) –0.27oC
25. Calculate the molality of methanol in a bottle of "methyl hydrate" used to help start
automobiles on damp days, if the solution is 90.0% CH3OH by mass. The molar mass of
methanol is 32.0 g · mol–1.
A) 0.320 m
B) 28.8 m
C) 2.81 m
D) 0.900 m
E) 281 m
26. Calculate the vapor pressure at 25oC of a mixture of benzene and toluene in which the
mole fraction of benzene is 0.800. The vapor pressure at 25oC of benzene is 94.6 Torr
and that of toluene is 29.1 Torr.
A) 81.5 Torr
B) 69.9 Torr
C) 105 Torr
D) 75.7 T0rr
E) 124 Torr
Short-answer Questions (4 marks each)
27. If the standard enthalpy of combustion of cyclohexane, C6H12(g), is –3953 kJ · mol–1,
how many liters of cyclohexane measured at 25oC and 107.2 kPa must be burned to
liberate 1000.0 kJ of heat?
28. The absorbance of a dye at 660 nm in a 1 cm cell is 0.761. If the concentration of the dye
is 5.40 ´ 10–4 M, calculate the molar absorption coefficient of the dye. Describe the color
and intensity of the solution of the dye.
29. Given the following data, calculate the second electron affinity of oxygen.
enthalpy of formation of Ca(g): 178 kJ · mol–1
first ionization energy of Ca(g): 590 kJ · mol–1
second ionization energy of Ca(g): 1150 kJ · mol–1
enthalpy of formation of O(g): 249 kJ · mol–1
first electron affinity of O(g): -141 kJ · mol–1
lattice enthalpy of CaO(s): 3505 kJ · mol–1
enthalpy of formation of CaO(s): –635 kJ · mol–1
30. Describe the bonding in acetonitrile, CH3CN.
31. Rhodium has a density of 12.4 g · cm–3 and an atomic radius of 134 pm. What is the
structure of the solid?
32. The addition of 1.96 g of vitamin B12, isolated as cyanocobalamin, to 100 g camphor
lowers the freezing point by 0.57oC. What is the molar mass of vitamin B12? The kf for
camphor is 39.7 K · kg · mol–1.
Long-answer Questions (6 marks each)
33. Draw the Lewis structure of XeF6 and predict this molecule's shape using VSEPR theory.
What are the bond angles?
34. Potassium chloride has an NaCl-type cyrstal structure. If the density of potassium
chloride is 1.984 g/cm3, determine the length of an edge of the unit cell.
35. Explain FIVE of the following terms and give examples where
illustrate your definition.
a.
VSEPR
b.
dipole moment
c.
resonance
d.
Boyle's Law
e.
partial pressure
f.
ppm
g.
Henry's Law
appropriate to
36. Cobalt(II)chloride exists as a hydrated salt that can be represented by the formula CoCl2 .
xH2O. In an experiment to determine the exact formula of this hydrated salt, 1.024 g of
the hydrate was dissolved in 250 mL of water and excess sodium hydroxide was added to
the resulting solution. The reaction that occured produced 0.573 g of cobalt(II)hydroxide.
Determine the formula of hydrated cobalt(II)hydroxide (i.e. the value of x in CoCl2 .
xH2O)
*** END OF EXAMINIATION ***
Final Examination Chemistry 217
Answer Key
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
D
B
D
A
C
A
B
D
E
E
E
B
B
B
A
A
A
A
D
E
E
A
B
A
E
A
Moles cyclohexane = (1000 kJ)/(3953 kJ/mol) = 0.2530 mol
Volume cyclohexane = nRT/P
= (0.2530 mol)(0.0821)(298 K)/(107.2/101.3 atm)
= 5.85 L
28. A = C (conc)(path length)
0.761 = C (5.40 ´ 10–4 M)(1 cm)
C = 1.41 x 103
660 nm absorbs in red therefore expect blue/green colour.
A is large therefore very intense colour.
29. O-(g) ====> O2-(g)
?
O(g) ====> O-(g)
-141
249
1/2O2(g) ====> O(g)
+
2+
Ca (g) ====> Ca (g)
1150
590
Ca(g) ====> Ca+(g)
Ca(s) ====> Ca(g)
178
CaO(s) ====> Ca(s) + 1/2O2(g)
635
__________________________________________
CaO(s) ====> Ca2+(g) + O2-(g)
3505
? = 844 kJ/mol
30. sigma single bonds for all C-H and C-C using sp3 orbitals
on the methyl carbon and sp orbitals on the central carbon
one sigma bond C-N using sp orbitals on carbon and nitrogen
two pi bonds C-N using 2 p orbitals on carbon and nitrogen
31. Assume fcc and try.
Volume = (81/2 r)3 = (83/2)(1.34 x 10-8 cm)3 = 5.44 x 10-23 cm3
Mass of one Rh atom = (102.9 g/mol)/(6.022 x 1023 atoms/mol)
= 1.709 x 10-22 g
Density = 4(1.709 x 10-22 g)/(5.44 x 10-23 cm3) = 12.5 g/cm3
Therefore it is face-centred cubic structure
32. DT = ikf x molality
0.57oC = (1)(39.7 K kg/mol)(molality)
molality = 1.4358 x 10-2 mol/kg = (1.96 g/MWt (B12))/0.100 kg)
MWt(B12) = 1365 g/mol
33. F6Xe: Shape based on a pentagonal bipyramid--distorted octehedral
All 90o.
34. 4 KCl per unit cell
Wt of 4KCl = 4(39.1 g/mol + 35.35 g/mol)/6.023 x 1023
= 4.95102 x 10-22 g
Volume = (4.95102 x 10-22 g)/(1.984 g/cm3) = 2.495 x 10-22 cm3
Edge Length = (Volume)1/3 = 6.29 x 10-8 cm or 6.29 A
35. a. VSEPR - valence-shell electron-pair repulsion model to predict geometric "shape"
around a central atom
b. diplole moment - a measure of separation between positive and negative centres in
polar molecules
c. resonance - 2 or more structures describing a molecule where the average gives a real
description
d. Boyle's Law - at constant T PV is a constant
e. partial pressure - pressure exerted by a particular gas in a mixture
f. ppm - part per million
g. Henry's Law - concentration of a gas in a solution is proportional to the pressure of
the gas over the solution (Cg = kPg)
36. 0.573 g of Co(OH)2 ===> 6.16 x 10-3 moles
Moles of CoCl2 . xH2O = Moles of Co(OH)2
MWt (CoCl2 . xH2O) = (1.024 g)/(6.16 x 10-3 moles) = 166.2 g/mol
CoCl2 . xH2O = 166.2
xH2O = 36.2
x = 36.2/18 = 2
CoCl2 . 2H2O