CHEM 1A: Final Exam Practice Problems:
These questions have been compiled from my final exams of previous years. That being said, these practice
problems are not a comprehensive list of all questions that could be asked on the exam. Refer to the
suggested textbook HW, other practice problems on the review materials page, iclicker questions, old quizzes
& challenge problem sets for a comprehensive review.
READ QUESTIONS CAREFULLY.
Answer the following questions in the spaces provided. Show all work and express final answers with the
correct number of significant figures and units to receive full credit. For multiple choice problems, circle all
answers that apply.
1. Which isotope of Aluminum has the same number of protons as Chlorine-35?
a. Aluminum-26
b. Aluminum-29
c. Aluminum-31
d. Aluminum-33
e. None of the above.
2. Which isotope of Chlorine has the same number of neutrons as Aluminum-33?
a. Chlorine-34
b. Chlorine-35
c. Chlorine-36
d. Chlorine-37
e. None of the above.
3. Antimony (Sb) has two naturally occurring isotopes, Antimony-121 (with a mass of 120.90 amu) and Antimony123 (with a mass of 122.90 amu). Which isotope is more abundant?
a. Sb-121
b. Sb-123
c. Neither, they are both equally abundant
d. Cannot determine from information provided
4. Bromine has two naturally occurring isotopes, 79Br and 81Br. The experimentally determined average atomic
mass of bromine is 79.90 amu. What are the natural abundances of the two isotopes (in percent)? Assume 79Br
= 79.00000 amu and 81Br = 81.00000 amu.
5. A compound is found to have an empirical formula of NO2. If an individual molecule of this compound has
a mass of 184 g/mol, determine the molecular formula.
6. Arrange in order of INCREASING size: K, K+, Ca, Ca2+. Explain your reasoning.
7. If the N—N triple bond in nitrogen gas has a bond dissociation energy of 945 kJ/mol, calculate the maximum
wavelength of electromagnetic radiation (in nm) that could fully break the N≡N bond in N2.
Remember: One photon is required to break each bond. Therefore, a mole of photons is required to break a mole
of bonds.
8. Circle all of the d orbitals below.
9. Circle any of the electron dot structures below that could not exist as stable molecules or ions.
10. Two of the compounds below are gases, two are liquids and one is a solid under standard conditions.
A. First, write down the strongest intermolecular force present in each compound.
B. Then use the information from part A to predict the phase of each compound.
Compound
Strongest Intermolecular Force Present
Phase (s, l, g?)
CH3CH2CH3
CH3CH2CH2CH2Cl
CH3CH3
11. Rank the following compounds in order of increasing boiling point: H2O, H2S, H2Se, H2Te. Explain your reasoning
by describing the type of intermolecular forces present in each substance.
Low boiling → High Boiling
12. Consider the three closed flasks represented below. The circles represent gas phase particles, and the shaded
rectangular area represents the liquid phase.
If the flasks separately contain H2O, CH3Cl and C2H2 at the same temperature, which is the correct assignment of flasks?
A)
B)
C)
D)
E)
F)
I = H2O, II = CH3Cl, III = C2H2
I = CH3Cl, II = C2H2, III = H2O
I = C2H2, II = CH3Cl, III = H2O
I = H2O, II = C2H2, III = CH3Cl
I = C2H2, II = H2O, III = CH3Cl
Cannot determine from information provided.
13. Write four reasonable resonance structures for the perchlorate anion, ClO4-. Include formal charge labels in one
structure. Be sure to minimize formal charge.
14. A. Given the six resonance structures for sulfate (SO42-) below, what is the overall bond order of the S—O bond?
HINT: Remember to consider the effects of resonance.
B. What is the molecular shape AND hybridization about the central sulfur atom above?
15. A. Draw a complete Lewis electron dot diagram for the XeF4 molecule.
B. Use the diagram above to predict: (a) the molecular shape of XeF4; (b) the hybridization of the central Xe
atom; (c) the approximate bond angles; (d) is XeF4 polar or nonpolar?
16. As a helium balloon rises in altitude, what would happen to the balloon?
A. The volume of the balloon would remain constant.
B. The volume of the balloon would decrease.
C. The volume of the balloon would increase.
D. Cannot determine from information provided.
17. The friction of tires against a roadway causes the rubber to heat up. Assuming a fixed tire volume, how would
you expect the pressure inside the tires to change as this happens?
A. The pressure will remain constant
B. The pressure will go down
C. The pressure will go up
D. Cannot determine from information provided.
18. Under what conditions are you MOST likely to observe ideal gas behavior?
A. High Temperature, High Pressure
B. Low Temperature, High Pressure
C. Low Temperature, Low Pressure
D. High Temperature, Low Pressure
19. When measured at 23.4 oC and 734.3 torr, an unknown gas has a density of 1.427 g/L. Calculate the molar mass
of the unknown gas.
20. Match the reactions on the LEFT with the reaction types on the RIGHT.
________
Ca3(PO4)2 + 6 CuCl → 3 CaCl2 + 2 Cu3PO4
A. Synthesis
________
CaO + CO2 → CaCO3
B. Double Replacement
________
2 C8H18 + 25 O2 → 16 CO2 + 18 H2O
C. Decomposition
________
2 LiCl + H2 → 2 Li + 2 HCl
D. Single Replacement
________
2 AlCl3 → 2 Al + 3 Cl2
E. Combustion
21. Write the balanced equation that describes the chemical transformation that occurs when aqueous solutions of
barium nitrate and ammonium sulfate are mixed. Predict if a solid will form and write phase symbols for each
species in the chemical reaction.
22. Consider the reaction of uranium (IV) oxide with hydrofluoric acid to produce uranium (IV) fluoride and water.
A. If 10.0 g of UO2 is treated with a solution containing 1.88 g of HF, what is the limiting reagent?
B. If only 4.55 grams of UF4 is produced, determine the percent yield.
23. A. An aqueous solution of lead (II) bromide has an overall concentration of 110. ppm. Determine the
concentration of lead ions (Pb2+) in moles per liter (mol/L). Assume the density of the solution is 1.00 g/mL.
B. If 50.00 mL of the solution above was diluted to a final volume of 250.0 mL, calculate the final molarity of
lead ions.
24. A compound is composed only of Carbon, Hydrogen and Bromine, and is known to have the percent
composition data below:
 85.9% Bromine by mass
 12.9% Carbon by mass
 1.2% Hydrogen by mass
A. Use the data above to determine the empirical formula for this substance.
B. Circle any of the compounds below that are consistent with the empirical formula you calculated in Part A
(above).
C. Place a star next to any of the compounds shown above that would be NONPOLAR molecules.
25. A. Using the information below, calculate the average bond dissociation energy of the triple bond (C≡O) in
carbon monoxide, in kJ/mol.
2 CO(g) + 2 H2O(g) → 2 CO2 + 2 H2(g)
ΔHrxn = -82.2 kJ
Average Bond Dissociation Energies (BDE) in kJ/mol:
C—O: 358
H—O: 467
C═O: 799
O—O: 204
H—H: 432
O═O: 498
C—H: 413
C—C: 347
C═C: 614
C≡C: 839
C≡O: ________
B. Using the enthalpy of reaction from above (ΔHrxn), calculate how much heat would be produced (in kJ), if
11.2 Liters of carbon monoxide (at STP, Standard Temperature and Pressure) fully reacted according to the
equation above.
26. Tetraphosphorus gas reacts with chlorine gas to generate a liquid, polar, molecular compound. Predict the
product of this reaction, write the balanced chemical equation then determine the heat of the reaction (qreaction)
if 25.0 g of tetraphosphorus reacted with 50.0 grams of chlorine gas to produce this compound.
27. Dichromate (Cr2O72-) reacts with nitrous acid (HNO2) to produce chromium (III) ions and nitrate ions (NO3-). Write
the balanced half reactions for this redox process, then write the complete balanced reaction in acidic
conditions.
a. (5 points) Reduction [r] Half-Reaction:
b. (5 points) Oxidation [o] Half-Reaction:
c. (5 points) Complete Balanced Equation (under ACIDIC conditions):