CHEM 3: Final Exam—Summer 2015
Name:____________________________________________
INSTRUCTIONS: On the front and back of the scantron, fill out your name and 7-digit student ID. Fill in this
information from left to right in the provided fields, and bubble in the values on the scantron. 1 point will be
deducted from your exam grade for incomplete or erroneous filling of the scantron.
Please read each question carefully. Where the question specifies “MARK ALL THAT APPLY”, you MIGHT need to
select more than one answer on the scantron.
1.
How many significant figures should be reported in the answer to the calculation below?
(0.021 𝑔 − 0.0184 𝑔)
=?
45.89 𝑚𝐿
A. 0 significant figures
B. 1 significant figure
C. 2 significant figures
D. 3 significant figures
E. 4 significant figures
2.
An electromagnetic wave has a wavelength of 0.594 µm. What is the frequency of this light in GHz?
Hint: 1 GHz = 1 x 109 Hz
A. 5.05 x 105 GHz
B. 1.98 x 10-15 GHz
C. 5.04 x 108 GHz
D. 1.98 x 10-9 GHz
E. None of the above are correct.
3. How many atoms of iron are in 12.9 g of iron?
Information that MIGHT be useful: Iron has a density of 7.87 g/mL, and an atomic mass of 55.85 amu.
A. 7.77 x 1024 atoms
B. 9.87 x 1023 atoms
C. 6.022 x 1023 atoms
D. 1.39 x 1023 atoms
E. 5.51 x 1025 atoms
4. How many moles of gold (Au) are present in a tiny speck of gold with a volume of of 0.159 mm3?
Information that MIGHT be useful: Gold has a density of 19.32 g/cm3, and an atomic mass of 196.96 amu.
A. 1.56 x 10-5 mol Au
B. 4.18 x 10-8 mol Au
C. 1.56 x 10-3 mol Au
D. 1.62 mol Au
E. None of the above are correct.
5.
MARK ALL THAT APPLY: How does the NEUTRAL neon-20 isotope compare to the DIANION of the oxygen-18
isotope, 𝟏𝟖𝑶𝟐− ?
A. They have different number of neutrons.
B. They have different number of protons.
C. They have different number of electrons.
D. They have different relative masses.
E.
All of the above.
6.
Naturally occurring Chlorine consists of the two stable isotopes below, and has an average atomic mass of 35.45
amu. Based ONLY on this information, which isotope is most abundant in nature?
Chlorine Isotope
Isotopic Mass (amu)
A.
Chlorine-35
34.968853
B.
Chlorine-37
36.965903
C.
They are both EQUALLY abundant.
D.
Cannot be determined from information provided. Additional mass spectrometry data
would have to be collected and analyzed.
7.
How many total VALENCE electrons should be included in the Lewis dot structure of a carboryne polyatomic dianion
with the formula B10C2H102-?
A. 40
B. 46
C. 48
D. 50
E. 90
8.
What is the electron configuration of a Mg2+ cation?
A. 1s22s22p6
B. 1s21p62s2
C. 1s22s23s23p4
D. 1s22s22p63s2
E. 1s22s22p63s23p6
9.
An unknown hydrocarbon (CxHY) is composed of 81.71 % carbon by mass. What is the empirical formula of this
substance?
A. C5H
B. C7H18
C. C3H8
D. C2H5
E. CH3
10. Carboranes are cage-like clusters made up of boron, carbon and hydrogen atoms bonded together in polyhedron
shapes. These molecules have been used to make superacids that are a million times stronger than sulfuric acid, and
are important elements in neutron capture therapy for treating cancer.
One such common carborane has an empirical formula of CB5H6. If the molecule is found to have a molar mass of
144.2 g/mol, what is the molecular formula of this substance?
A. In this case, the molecular formula is the same as the empirical formula: CB5H6
B. C2B10H12
C. C3B15H18
D. C2B5H6
E. Cannot determine from information provided—the isotopic abundance data would have to be collected.
11. Hypophosphite salts are important reagents in electroless nickel plating, which is used in everything from coating
door handles to manufacturing hard disk drives. Which Lewis dot structure below is the most reasonable
representation for the hypophosphite anion, H2PO2-?
A.
B.
C.
D.
E.
HINT for Questions 12-15: Be sure to consider the three-dimensional shape of the molecule overall. As inherently limiting twodimensional drawings, the Lewis dot structures, when first drawn, do NOT necessarily reflect the spatial arrangements of the
atoms in the larger molecule. VSEPR THEORY SHOULD BE USED TO PREDICT SHAPES BASED ON LEWIS DOT STRUCTURES.
12. Given the Lewis dot structure below and your understanding of VSEPR Theory, predict the ELECTRON geometry at the
central tellurium atom.
A. bent
B. linear
C. trigonal planar
D. tetrahedral
E. trigonal pyramidal
13. Flumethrin is a common insecticide used externally in veterinary medicine against parasitic insects and ticks on cattle,
sheep, goats, horses, cats and dogs. Given the Lewis dot structure for Flumethrin below, predict the MOLECULAR geometry
at the highlighted carbon atom.
A. bent
B. linear
C. tetrahedral
D. trigonal planar
E. trigonal pyramidal
14. The substance, Imidacloprid, is currently the most widely used insecticide in the world. Given the Lewis dot structure of
Imidacloprid below, predict the approximate carbon-nitrogen-nitrogen (C-N-N) bond angle as highlighted in the structure.
A. 60o
B. 90o
C. 109.5o
D. 120o
E. 180o
15. MARK ALL THAT APPLY: Based on the Lewis dot structures below and your understanding of VSEPR Theory, predict
which compounds would be NONPOLAR.
A.
B.
C.
D.
E. None of these
molecules are NONPOLAR
16. We’ve learned so much, and come so far in just 6 weeks. Kinda demonstrates what might be possible in the span of 4 years
of intense learning, let alone an entire lifetime, huh?
A. This isn’t really a chemistry question. Mark A on the scantron for a bonus point for all of your hard work.
A. No, really. Mark A for a free point.
17. Determine the molar mass of an unknown gas with a density of 4.315 g/L at a pressure of 98.37 kilopascals (kPa) and a
temperature of 25 oC.
HINT: You’ll likely need to consult the conversion factors on the back page of the exam for this problem. Pay attention to units!
A. 1.07 g/mol
B. 68.4 g/mol
C. 109 g/mol
D. 815 g/mol
E. None of the above are correct.
18. When properly balanced with the smallest whole number coefficients, what is the stoichiometric coefficient on the oxygen
molecules (O2) in the reaction below?
_____ C21H30O2 + _____O2(g) → _____ CO2(g) + _____ H2O(g)
A.
B.
C.
D.
E.
16
32
34
36
42
19. What volume of 5.00 M nitric acid should be diluted to reach a final concentration of 0.250 M with an end volume of 500.0
mL?
A. 2.50 mL
B. 0.0250 L
C. 0.250 L
D. 250. mL
E. 625 mL
20. What is the mass percent of a solution formed by dissolving 5.000 g of ammonium phosphate (NH4)3PO4 in 20.00 mL of
water? Assume the density of the water is 0.9987 g/mL.
A. 20.00 %
B. 20.21 %
C. 25.00 %
D. 25.33 %
E. 24.68 %
21. How many moles of CHLORIDE ions are present in 750 mL of an aqueous solution of 4.00 M AlCl3?
A. 3.0 moles
B. 4.0 moles
C. 6.0 moles
D. 7.5 moles
E. 9.0 moles
22. What is the pH of a 7.9 x 10-5 M aqueous solution of HClO4 (a strong acid)?
A. pH = 3.10
B. pH = 4.10
C. pH = 4.79
D. pH = 5.79
E.
pH = 9.90
23. What is the concentration of hydrogen ions, [H+], in aqueous potassium hydroxide (a strong base) with a pH = 10.2?
A. 2 x 10-10 M
B. 1.00 x 10-14 M
C. 6 x 10-11 M
D. 1.58 x 10-4 M
E. 1.58 x 1010 M
24. What minimum volume of 0.150 M HCl solution (a strong acid) would be needed to fully neutralize 45. mL of 0.300 M
NaOH solution (a strong base)?
A. 90. mL
B. 20. mL
C. 13.5 mL
D. 2.02 mL
E. None of the above are correct.
25. Consider the acid-base reaction below:
3 Mg(OH)2(aq) + 2 H3PO4(aq) → 6 H2O(l) + Mg3(PO4)2(s)
Consider the mixing of 30.0 mL of 3.00 M aqueous magnesium hydroxide solution with 120.0 mL of 0.500 M H3PO4 solution.
Under these conditions, what would be the limiting reagent?
A. Mg(OH)2(aq)
B. H3PO4(aq)
C. H2O(l)
D. Mg3(PO4)2(aq)
E. There would be no limiting reagent: Everything would fully react.
FREE RESPONSE:
1.
Complete the table below by writing the formulas or names as necessary.
Formula
Systematic Name
H3PO4
Hydroiodic acid
Cl2O6
tin (IV) nitride
In2O3
2.
Aqueous sodium carbonate reacts with aqueous nitric acid to generate gaseous carbon dioxide, liquid water and aqueous
sodium nitrate.
A. Write the balanced chemical equation for this process, including phases.
B. Following the equation above, how many milliliters of 0.250 M aqueous sodium carbonate solution are necessary to
generate a theoretical yield of 125 mL of carbon dioxide gas at standard temperature and pressure?
C.
3.
If only 120 mL of the gas was actually produced in the neutralization from part B above, what was the percent yield of
carbon dioxide?
An unknown compound dissolved in water with a concentration of 9.7 x 10-6 M has a pH of 9.28. Is this unknown compound
most likely a strong acid, weak acid, strong base or weak base. Briefly EXPLAIN YOUR REASONING. Include in your
explanation a calculation to support your reasoning.
EXTRA CREDIT: 15 points
Data from the Mauna Loa Observatory in Hawaii indicate the global concentration of carbon dioxide in the atmosphere – the primary
cause of human-driven climate change – has recently reached 400 parts per million (ppm) for the first time in recorded history. This is
100 ppm higher than any time in the last 1 million years.
According to the U.S. Energy Information Association (EIA), the current global combustion of gasoline (mostly C8H18) stands at roughly
22.0 x 109 barrels per year. Now let’s pretend there is a catastrophic event that halts all photosynthesis on Earth so that diatomic
oxygen gas is no longer being generated. Earth is a barren wasteland, and yet somehow the human race is able to survive this
apocalypse and continues to burn gasoline at the same constant rate. How many years (minimum) will it take before the mass percent
of carbon dioxide is equal to the mass percent oxygen in the atmosphere? 1 For the sake of simplicity & to keep this calculation on a
back of an envelope basis, assume the only change in mass of the atmosphere results from the consumption of diatomic oxygen and
the newly introduced carbon dioxide from gasoline combustion.2
Information that might be useful:
 1 barrel = 31.5 gallons
 1 gallon = 3.78 L
 Density of octane (C8H18) = 0.719 g/mL
 Boiling point of octane = 125 oC
 Solubility of octane in water: 0.007 mg/L at 20 oC
 Density of solid carbon dioxide = 1562 kg/m3 at 1 atm & -78.5oC
 Solubility of carbon dioxide in water: 1.45 g/L at 25 oC & 100 kPa
 Age of the Earth: 4.54 x 109 years
 Mass of the Earth’s atmosphere: 5.1 x 1018 kg
 Volume of Earth’s atmosphere: 4.2 x 109 km3
 Current Composition of Earth’s atmosphere (in mass percent):
o 75.47 % N2
o 23.20 % O2
o 1.28 % Ar
o 0.04 % CO2 (400 ppm)
o 0.01 % other gases
1.
2.
A possibility that seems absurd only until the history of our planet’s atmosphere is scrutinized—wherein we find an entire epoch that was defined by the
transformation of the atmosphere through the slow biological activity of microscopic blue-green algae. In a sense, we owe our vigorous activity and
existence as animals today to ancient microscopic cyanobacteria brethren that made life on Earth hospitable to diatomic oxygen respiring organisms.
Check out the Cambrian Explosion to learn more about this thrilling time period in Earth’s history, where drastic evolutionary changes were fueled in a
large part by atmospheric change.
A gross oversimplification indeed, but one that makes this a straightforward calculation to illustrate the insanely rapid pace at which even something as
large as the Earth’s atmosphere can change in a relatively short geological time scale.
FINAL EXAM REFERENCE INFORMATION:
𝑫𝒆𝒏𝒔𝒊𝒕𝒚 =
𝑀𝑎𝑠𝑠
P1V1 = P2V2
𝑉𝑜𝑙𝑢𝑚𝑒
P1/T1 = P2/T2 V1/T1 = V2/T2 V1/n1 = V2/n2
PV=nRT, where R = 0.08206 L·atm/mol·K = 62.37 L·torr/mol·K = 8.314 L·kPa/mol·K
Temperature Conversion: Kelvin = oC + 273.15
PRESSURE CONVERSIONS: 1.00 atm = 14.7 psi = 760. mmHg = 101.325 kPa = 1.013 bar = 760 torr
1.00 bar = 750.06 torr = 0.987 atm
At STP: Pressure = 1.000 atm, Temperature = 273 K & 1 mole of gas = 22.4 L
Average atomic mass = (isotopic mass)∙(isotopic abundance)
1 mole = 6.022 x 1023 particles
c = λ·ν
Molarity = (# of moles)/(volume in liters)
1 cm3 = 1mL
where c = 2.9979 x 108 m/s
Mass % = (Mass of Solute)/(Mass of Solution) x100
Ppm = (Mass of Solute)/(Mass of Solution) x 106
pH = -log[H+]
Summing over all isotopes.
[H+][OH-] = 1.00 x 10-14
Dilution Problems: M1V1 = M2V2
pH + pOH = 14
Table of Electronegativities