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Final Exam
Chemistry 1210
Spring 2002
Prof. Steve Scheiner
May 3, 2002
Instructions:
You may begin the exam at 9:30 AM. You have until 11:20 AM.
This exam has 50 questions. Each question is worth 2 points for a total of 100 points. You may use a calculator and may refer to a single sheet of paper with notes and formulae.
Use only a #2 Pencil to mark the best answer on the Scantron sheet. You will turn in only the Scantron sheet. You may keep the rest of the exam.
On the Scantron sheet, fill in your last name, first and middle initials, identification number (this is your social security number). Also fill in the appropriate bubbles. Your score on the exam will be sent to your University email address.
Useful Information:
A periodic table is found later in the exam.
moles = mass/molecular weightDensity = mass/volumeAvogadro’s number = 6.02 x 1023
F = (9/5)(C) + 32C = 5/9 (F – 32)K = C + 273
J = kg-m2/s2 kinetic energy = ½ mass x velocity2
speed of light c = 3.0 x 108 m/s
Planck’s constant h = 6.63 x 10-34 J-s
ideal gas law: pV = nRT osmotic pressure π=MRT
1 atm = 760 mm Hg = 760 torr = 101.3 kPa
gas constant R = 0.08206 L-atm/mol-K
1 Å = 10-10 m
1. Which of the following would be equivalent to 8.5 x 10-10 m?
a) 0.85 nmb) 85 pm
c) 85 kmd) 8.5 x 10-12 cm
a) 8.5 x 10-10 m = 0.85 x 10-9 m = 0.85 nm
2. A lake has a concentration of 7.0 ppm of the toxic material dioxin. If the total volume of the lake is 9.0 x 108 L, what is the total amount of dioxin in the lake?
a) 9.0 x 10-6 L b) 6.3 x 10-6 L
c) 6300 Ld) 7.7 x 102 L
c) 7.0 ppm = 7.0 x 10-6 dioxin/lake water. total amount of dioxin = conc x amount of lake water
= 7.0 x 10-6 x 9.0 x 108 L = 63 x 102 L = 6300 L
3. The density of a new light material is 0.64 g/mL. What will be the thickness of a sheet of this material that measures 30 cm wide by 2 m in length, if the total mass of this sheet is 768 g?
a) 20 cmb) 2 mm
c) 388 kgd) 7.2 mm
b) density = mass/volume = mass/(length x width x thickness) so
thickness = mass/(dens x length x width) = 768 g /(0.64 g/cm3 x 30 cm x 200 cm) = 0.2 cm
= 2 mm
4. The thermometer in a cold room reads -64° F. Which of the following expresses this same temperature in another scale?
a) -96° Cb) -35° C
c) 220 Kd) 53 K
c) (-64 - 32)5/9 = -53° C = 220 K
5. A bottle label says that it contains sodium sulfate. Which is the correct formula for this reagent?
a) Na(SO3)b) So2S
*c) Na2SO4d) Na(SO4)2
6. A substance is known to have the following empirical formula CH2O. Which of the following might represent its true molecular formula?
a) C128H64O128b) C3H6O6
c) C6H6O6*d) C12H24O12
7. An entity contains 80 protons, 120 neutrons, and 79 electrons. Which would be its correct designation?
a) 80Hg-b) 120Hg
*c) 200Hg+d) 80Hg+
8. The average atomic mass of tin is 118.7. If we assume that two isotopes of Sn occur naturally with masses 118.0 and 120.0, what is the natural abundance of the first isotope (118)?
a) 70%b) 65%
c) 40%d) 25%
b) 118.7 = a118(118) + a120(120) and a118 + a120 = 1
so 118.7 = a118(118) + (1-a118)(120) solving, get a118 = 0.65 = 65%
9. What is the percentage oxygen by weight in C6H5CO2H?
a) 13%b) 36%
c) 26%d) 1.8%
c) %O = mass of O/total MW = (2x16)/122 = 26%
10. How many Ca atoms are present in 0.4 g of this element?
a) 6.02 x 1023b) 6.02 x 1021
c) 0.01d) 0.4 x 1023
b) 0.4 g of Ca represents 0.4/40 moles = 0.01 moles
multiply by 6.02 x 1023 to get number of atoms, so 6.02 x 1021
11. A material is analyzed and found to contain 85% Sr by weight, and 15% O. What is its empirical formula?
a) SrO2b) Sr5O
c) Sr3Od) SrO
d) consider 100 g which contains 85 g of Sr (85/88 = 0.96 moles) and 15 g of O (15/16 = 0.94 moles) about as many moles of O as Sr so SrO
12. What is the oxidation number of the element N in Ba(NO2)2?
a) +1b) +5
c) +4*d) +3
13. What volume of a 0.25 M solution of KMnO4 would hold 0.05 moles of this substance?
a) 25 Lb) 200 mL
c) 2.0 Ld) 5 mL
b) M = n/V so V = n/M = 0.05 moles / 0.25 mole/L = 0.2 L = 200 mL
14. Consider the following reaction.
CH3OH(g) --> CO(g) + 2H2(g) ΔH= +90.7 kJ
How much heat is produced along with 16 g of H2 at constant pressure?
a) 363 kJb) 181 kJ
c) 90.7 kJd) 45.4 kJ
a) reaction as written specifies 2 moles of H2. 16 g of H2 represents 8 moles, or 4 times the amount, so multiply ΔH by 4 to get 363 kJ
15. The specific heat of copper metal is 0.385 J/g-K. How much energy is required to raise the temperature of 0.85 kg of copper from 22.5° C to 74.5° C?
a) 23.5 kJb) 7.4 J
c) 165 Jd) 17 kJ
d) q = mCΔT = 850 g x 0.385 J/g-K x (74.5 - 22.5) = 17020 J = 17 kJ
16. Which of the following represents a valid balanced equation that describes the formation of the product from its elements in their standard states?
a) 2 Na(s) + SO4(g) --> Na2SO4 (s)
b) 2 Al(s) + 3 O(g) --> Al2O3(s)
c) 2 C(gr) + O(g) + 6 H(g) --> C2H5OH (l)
d) 2 C(gr) + H2 (g) --> C2H2 (g)
d) only d contains elements in their standard states.
17. What is the wavelength of a microwave of frequency 5 x 1010 s-1 ?
a) 0.6 x 1010 mb) 167 m
c) 6 mmd) 1500 cm
c) λ = c/ν = 3.0 x 108 m/s / 5 x 1010 s-1 = 0.6 x 10-2 m = 6 mm
18. Which of the following sets of quantum numbers are not allowed for an electron in an atom?
a) n=6, l =2, ml =1
b) n=3, l =0, ml =0
c) n=3, l =2, ml =-1
d) n=2, l =2, ml =2
d) l can never be as large as n
19. When l =3, which is the correct listing of possible values of ml ?
*a) 3,2,1,0,-1,-2,-3b) 0,1,2
c) 2,1,0,-1,-2d) 3,2,1,0
20. What is the maximum number of electrons that can occupy the n=2 shell?
a) 4b) 18
*c) 8d) 2
21. Which element below is likely to have a smaller first ionization energy than does Na?
*a) Kb) Ar
c) Cld) N
22. Which of the following is least likely to be ionic?
a) CaCl2*b) NO2
c) Cs2Od) MgCl2
23. Which type of atom might have an electron configuration that ends with ns2?
a) alkali metalb) halogen
c) inert gas*d) alkaline earth metal
24. An electron has mass 9.1 x 10-31 kg. What is the total kinetic energy of a mole of electrons, all moving at a velocity of one tenth the speed of light?
a) 247 MJb) 1.4 x 10-23 J
c) 41 x 1023 Jd) 2.5 x 1023 J
a) kinetic energy = ½ mass x velocity2 = ½ x 9.1 x 10-31 kg (3.0 x 107 m/s)2 x 6.02 x 1023
= 2.47 x 108 J = 247 MJ
25. How many valence electrons does an atom have if it has the following electron configuration:
1s22s22p63s2
*a) 2b) 12
c) 3d) 8
26. Which of the following is likely to have the smallest lattice energy?
a) NaIb) MgCl2
c) CaOd) AlCl3
a) NaI has ions with charges of +1 and -1.
27. Which of the following correctly lists the order of atomic or ionic size?
a) I- < I < I+*b) Fe+3 < Fe+2 < Fe
c) Na+ < Li < Li+d) Kr < Ar < Cl
28. Which is the correct order of increasing electronegativity?
a) F < O < Nb) As < Co < K
c) C < Si < Ge*d) As < S < F
29. Which species below violates the octet rule?
a) NH3b) CH4
*c) PCl5d) SiO2
30. A central atom contains 4 bonding domains and 2 nonbonding domains. What is the most likely molecular geometry?
a) tetrahedralb) see-saw
*c) square planard) trigonal biplanar
31. Which would be the best description for the shape of the SF4 molecule?
a) square planarb) see-saw
c) tetrahedrald) square pyramid
b) 4 bonding domains, and 1 nonbonding domain.
32. Which molecule would you predict to be nonpolar?
a) COb) CF4
c) CHCl3d) IF5
b) CF4 is tetrahedral, like CH4, so all bond dipoles cancel
33. According to molecular orbital theory, which of the following should have the weakest bond (lowest bond order)?
a) O2b) N2+
c) F2d) F2-
d) bond order of F2- is only ½
34. What would happen to the temperature inside a cylinder if you lowered the pressure from 1 atm to 190 torr, while holding the volume constant?
a) the temperature would remain the same
b) the temperature would be increased by a factor of 4
c) the temperature would be decreased by a factor of 4
d) the temperature would be reduced by a factor of 190
e) it would go below absolute zero, and thereby fall into a black hole
c) since pV=nRT, T = pV/nR. V/nR constant so T directly proportional to p. 190/760 = ¼.
35. What is the pressure of 600 mL of 0.5 moles of an ideal gas, if the temperature is 25° C?
a) 1.7 atmb) 20 atm
c) 15 torrd) 37 torr
b) pV=nRT, so p=nRT/V = 0.5 mole x 0.08206 L-atm/K-mole x 298 K/0.6 L = 20.4 atm
36. Which of the following gases would you expect to be the least dense at 40 torr and at a temperature of 50 K?
a) O2b) NH3
c) CO2d) C3H8
b) density is proportional to MW
37. Which is the correct order of increasing molecular disorder?
a) liquid < solid < gasb) gas < liquid < solid
*c) solid < liquid < gasd) solid < gas < liquid
38. Which types of intermolecular forces are present in a sample of CH3OCH3?
a) ion-dipole and dipole-dipole
b) hydrogen bonds and dispersion
c) dipole-dipole, dispersion and hydrogen bonds
*d) dipole-dipole and dispersion
e) love and affection
39. The condensation of water vapor to liquid droplets in a cloud supplies a great deal of energy to fuel the formation of hurricanes and tornadoes. If the heat of vaporization of water is 2.4 kJ/g, how much energy will be supplied by the formation of a cloud containing 10,000 kg of water?
a) 10,000 kJb) 24,000 kJ
c) 24,000 MJd) 4167 kJ
c) q = ΔHvap x m = 2.4 kJ/g x 107 g = 2.4 x 107 kJ = 2.4 x 104 MJ = 24,000 MJ
40. You are told that substance A has a higher boiling point than substance B. What inference can you make about some of their other properties?
*a) intermolecular forces in A are stronger than in B
b) A has a higher vapor pressure than B at a given temperature
c) A has a lower molecular weight than does B
d) B forms hydrogen bonds but A does not
e) A stands for “apple” and B for “banana”
41. What is the best name for the process that occurs when one moves from the left to the right in a phase diagram crossing a phase change, below the triple point?
a) evaporation*b) sublimation
c) fusiond) deposition
e) subliminal advertising
42. An element crystallizes in a face-centered cubic unit cell of length 2.84 Å . If the density of this element is 6.32 g/cc, what is this element’s atomic weight?
a) 22b) 145
c) 45d) 87
a) density = m/V = 4 atoms x AW/ 6.02 x 1023 x V so AW = 6.02 x 1023 x V x density/4 =
= 6.02 x 1023 x (2.84 x 10-8 cm)3 x 6.32 g/cm3 /4 = 21.8
43. Which would be the best explanation why sweat cools your body as it evaporates?
a) sweat is produced by the sweat glands at a temperature well below body temperature
*b) the conversion of liquid water to vapor is endothermic
c) sublimation occurs for water at very low temperatures
d) sweating occurs at the triple point of water
e) sweating produces a natural desire to consume more Gatorade
44. The enthalpy of fusion of ethanol is 0.11 kJ/g at its freezing point of -114° C. The heat capacity of liquid ethanol is 2.3 J/K-g. How much heat is required to transform 100 g of solid ethanol at -114° C to liquid at -14° C?
a) 11 kJb) 23 kJ
c) 2300 kJd) 34 kJ
d) solid to liquid transition: q=ΔHfus x m = 0.11 kJ/g x 100 g = 11 kJ
temp rise of liquid from -114 to -14: q= mCΔT = 100 g x 2.3 J/K-g x 100 K = 23 kJ
sum of two results is 34 kJ
45. 20 g of C2H5OH (ethanol) are dissolved in 150 g of water. What is the correct mole fraction of ethanol in water?
a) 0.13b) 0.12
c) 0.003d) 0.05
d) C2H 5OH: n= 20 g/ 46 g/mol = 0.43 mole water: n = 150 g/ 18 g/mol = 8.33mole
X = 0.43/(0.43 + 8.33) = 0.05
46. Pure benzene freezes at 5.5° C, and has a freezing point depression constant of 5.12 °C/m. What would you expect the freezing point to be if 24 g of glucose (C6H12O6) is dissolved in 535 g of benzene?
a) -0.25° Cb) 1.3° C
c) 4.2° Cd) 5.8° C
c) n(glucose) = 24 g / 180 g/mol = 0.13 moles
m = n/kg solvent = 0.13/0.535 kg = 0.25 m
ΔTf = Kf x m = 5.12 °C/m x 0.25 m = 1.3°, subtracting this from 5.5 yields 4.2° C
47. Which of the following aqueous solutions would you predict to have the highest boiling point?
a) 0.06 m KBrb) 0.05 m CaCl2
c) 0.05 m NaCld) 0.02 m K3PO4
b) when 0.05 multiplied by 3 (particles of CaCl2) get 0.15, highest value of those shown
48. You are given a solution that is 6.5% by mass KCl in water. What is its correct molality?
a) 0.070b) 0.93
c) 0.088d) 8.7
b) assume 100 g of solution: 6.5 g KCl, 93.5 g water.
n(KCl) = 6.5/74.5 = 0.087 moles
molality = 0.087 moles/0.0935 kg = 0.93
49. A solution is prepared that contains 0.250 g of a substance X dissolved in 250 mL of aqueous solution. If the osmotic pressure of this solution is 1.20 torr at 30° C, what is the molecular weight of X?
a) 15,700b) 21
c) 1560d) 48
a) π=MRT = (n/V)RT = (m/[MWxV])RT so MW = mRT/πV
MW = 0.25 g x 0.08206 L-atm/K-mol x 303 K /([1.2/760] atm x 0.25 L) = 15,700
50. Which is the best explanation for the observation that living cells are enlarged to the point of bursting when immersed in distilled water?
a) the concentration of salts within the cell reduce its freezing point
b) the semipermeable membrane of the cell allows salt to exit from the cell into the surroundings
*c) the concentration of salts within the cell causes water from outside to enter the cell
d) the salts within the cell dissociate to multiple ions
e) living cells contain tiny little bombs that explode when the cell is placed under a microscope