Name______________________________________
Student ID Number___________________________
TA Name___________________________________
Lab Section_________________________________
Winter 2016 - Enderle
CHEMISTRY 2A
Exam I
Multiple Choice (circle one)
Instructions:
CLOSED BOOK EXAM! No books, notes, or additional scrap paper are
permitted. All information required is contained on the exam. Place all work
in the space provided. If you require additional space, use the back of the
exam.
(1) Read each question carefully.
(2) There is no partial credit for the problems in Part I and Part II. You will
lose 10 points if you do not circle your multiple choice answers on the
front page or if you do not write your TA’s name or section in the space
above.
(3) The last page contains a periodic table and some useful information.
You may remove this for easy access.
(4) Graded exams will be returned in the laboratory sections next week.
(5) If you finish early, RECHECK YOUR ANSWERS!
U.C. Davis is an Honor Institution
Possible Points
1–14. 42 points
15. 06 points
16–18. 22 points
19. 11 points
20. 10 points
21. 15 points
Total Score (106)
Points
1.
A
B
C
D
E
2.
A
B
C
D
E
3.
A
B
C
D
E
4.
A
B
C
D
E
5.
A
B
C
D
E
6.
A
B
C
D
E
7.
A
B
C
D
E
8.
A
B
C
D
E
9.
A
B
C
D
E
10.
A
B
C
D
E
11.
A
B
C
D
E
12.
A
B
C
D
E
13.
A
B
C
D
E
14.
A
B
C
D
E
Exam I
Page 2 of 9
Part I: Multiple Choice
Circle the correct answer here and on the cover – No partial credit (3 points each)
1. Dalton’s atomic theory predicted that elements in compounds combine in small whole
number ratios. What is this law called?
A. Conservation of Mass B. Constant Composition C. Definite Proportions
D. Multiple Proportions
E. Avogadro
2. What is the approximate percent by mass of hydrogen in C2H6 (molar mass = 30.068 g/mol)
A. 6
B. 20
C. 24
D. 60
E. 80
3. Identify the unknown isotope (X) that has one more neutron than protons and a mass number
equal to nine times the charge on the ion X3+.
A. B
B. C
C. Al
D. Si
E. Ge
4.
What multipliers are needed for the three respective simultaneous reactions below, in order
to obtain this overall reaction: 2 Al (s) + 3 Cl2 (g) → 2 AlCl3 (s)?
Find the multipliers (α, β, γ, δ). [2 Al (s) + 6 HCl (aq) → 2 AlCl3 (aq) + 3 H2 (g)] x α
[HCl (g) → HCl (aq)] x β
[H2 (g) + Cl2 (g) → 2 HCl (g)] x γ
[AlCl3 (s) → AlCl3 (aq)] x δ
A. 1, 6, 3, -2
B. -1, -3, 6, 2
C. -1, 6, 3, -2 D. 1, 0, 3, -1 E. 1, 1, 1, 1
5. If these cations (Hg2+, Ba2+, Pb2+, Fe3+, & K+) were added to an aqueous solution containing
the sulfide ion, which of the following would likely precipitate? If there is more than one answer,
then circle all correct answers.
A. HgS
B. BaSO4
C. PbSO4
D. Fe2S3 E. K2S
6. The halogen that most likely has a -1 oxidation state is ________.
A. F
B. Cl C. Br D. I E. At
7. How many H atoms are in the molecule shown here?
A. 2 B. 8 C. 12 D. 14 E. 18
8. How many hydrogen atoms are present in a 154.3 g sample of C12H26?
A. 5.454 x 1026 B. 2.186 x 1021 C. 7.184 x 1022 D. 1.418 x 1025
9. Which of the following is a strong acid?
A. HF
B. H2O C. HC2H3O2 D. H2SO4
E. 7.184 x 1024
E. HNO2
10. How many mL of water must be added to 25 mL of 0.75 M HCl (aq) to make a 0.15 M HCl
(aq) solution?
A. 25.0 mL B. 50.0 mL C. 75.0 mL D. 100.0 mL E. 125.0 mL
Exam I
Page 3 of 9
11. Magnesium has 3 stable isotopes with masses of 23.98504, 24.98584, and 25.98259
respectively. Mg-25 is 10.13%. What are the percentages of the other two isotopes? (The atomic
mass of magnesium is 24.3050 u.)
A. 78.9% and 10.9% B. 50% and 50% C. 44.9% and 44.9%
D. 83.6% and 16.4% E. 78.9% and 21.1%
12. What is the molarity of 10.9 g KCl dissolved in 150.0 mL of water?
A. 0.0727 M B. 0.146 M C. 0.975 M D. 0.0219 M E. 0.667 M
13. What volume of 0.561 M KMnO4 (aq) is necessary to exactly react with 6.54 g KI in the
following reaction? 2 KMnO4 + 10 KI + 8 H2SO4 → 6 K2SO4 + 2 MnSO4 + 5 I2 + 8 H2O
A. 0.0140 mL B. 1.20 mL C. 14.0 mL D. 163.2 mL E. impossible to determine
14. The relative abundance of lead-204 in lead is 1.48%. What size block of lead (in cubic
centimeters) will contain 8.34 × 1021 atoms of lead-204? The density of lead is 11.35 g/cm3.
A. 0.253 B. 17.1 C. 17.4
D. 194
E. 253
Part II: Short Answer
Fill in the blank. No partial credit for work shown.
15. (6 points) Provide the oxidation states for the elements indicated in the table.
Compound
Provide the oxidation state here
for the following elements
ClF (g)
Cl: +1
[Cu(CO)5F]2CO3 (aq)
Cu: +2
How many protons are in ClF? 26
Exam I
Page 4 of 9
16. (4 points) Balance the following reactions using coefficients in terms of the variables w, x, y,
and z. One of the coefficients is done for you.
1 CxHyNwOz + __________________ O2 → ________ CO2 + ________ H2O + ________ NO2
Answer: 1, ½(2x+y/2+2w-z) → x,y/2,w
17. (3 points each, 6 total) Write the balanced net ionic chemical equation for the following
reactions (include states for each species).
A. Al metal reacts with hydrochloric acid.
2Al (s) + 6 HCl (aq) → 2AlCl3 (aq) + 3H2 (g)
2Al (s) + 6 H+ (aq) → 2Al3+ (aq) + 3H2 (g)
B. Calcium carbonate reacts with nitric acid.
CaCO3 (s) + 2 HNO3 (aq) → Ca(NO3)2 (aq) + CO2 (g) + H2O (l)
CaCO3 (s) + 2H+ (aq) → Ca2+ (aq) + CO2 (g) + H2O (l)
18. (12 points) Fill in the blanks of the table giving the chemical name or chemical formula.
Chemical Formula
Chemical Name
S2F10
disulfur decafluoride
Sr3N2
strontium nitride
HNO2
nitrous acid
HI (aq)
hydroiodic acid
Hg2Cl2
mercurous chloride
CH4
methane
Exam I
Page 5 of 9
Part III: Long Answer
Please show all work – Partial credit – Use the correct number of significant figures
19. (11 total points) Given the reaction: PbO2 (s) + S (s) → Pb2+ (aq) + SO2 (g)
a) (1 pt each—2 total) Which reactant is reduced? Which reactant is oxidized?
Reduced:
PbO2 (s)
Oxidized: S (s)
b) (3 points) Balance the reduction half reaction (acidic solution).
2e− + 4H+ (aq) + PbO2 (s) → Pb2+ (aq) + 2H2O (l)
c) (3 points) Balance the oxidation half reaction (acidic solution).
S (s) + 2H2O (l) → 4e− + 4H+ (aq) + SO2 (g)
d) (3 points) Give the overall reaction with state symbols in acidic conditions.
4H+ (aq) + 2PbO2 (s) + S (s) → 2Pb2+ (aq) + 2H2O (l) + SO2 (g)
Exam I
Page 6 of 9
20. (10 points total) 0.1005 g of menthol is combusted, producing 0.2829 g of CO2 and 0.1159 g
of H2O. Menthol contains carbon, hydrogen, and oxygen atoms.
A. (8 points) Find the empirical formula of menthol
C: 0.2829 g x ((1 mol/1mol) ÷ 44.0098) = 0.006428 mol C
H: 0.1159 g x ((2 mol/1 mol) ÷ 18.0152) = 0.01287 mol H
C: 0.006428 mol (12.011 g/mol) = 0.07721 g C
H: 0.01287 mol (1.008 g/mol) = 0.01297 g H
O: 0.1005 - (0.07721 + 0.01297) = 0.01032 g
O: 0.01032 g ÷ 15.999 g/mol = 0.0006452 mol
C: 0.006428 mol ÷ 0.0006452 mol = 9.96
H: 0.01287 mol ÷ 0.0006452 mol = 19.94
O: 0.0006452 mol ÷ 0.0006452 mol = 1
C10H20O
Empirical
Formula
B. (2 points) What is the molecular formula of menthol (156.3 u)?
𝟏𝟓𝟔. 𝟑
=𝟏
𝟏𝟓𝟔. 𝟐𝟕
𝑴𝒐𝒍𝒆𝒄𝒖𝒍𝒂𝒓 𝒇𝒐𝒓𝒎𝒖𝒍𝒂 = 𝑪𝟏𝟎 𝑯𝟐𝟎 𝑶
𝑪𝟏𝟎 𝑯𝟐𝟎 𝑶 → 𝟏𝟓𝟔. 𝟐𝟕𝒖 Molecular
Formula
Exam I
Page 7 of 9
21. (15 points total) When 120.0 g of C7H16 (l) is combusted with 350.0 g of O2 (g), 300.0 g of
CO2 (g) is collected in a laboratory.
A. (3 points) Write the combustion reaction and balance.
C7H16 (l) + 11 O2 (g) → 7 CO2 (g) + 8 H2O (l)
B. (5 points) What mass of CO2 (g) could theoretically be produced in this reaction?
Fuel: 120.0 g (mol/100.198 g)(7 mol/1 mol)(44.01 g/mol) = 368.95 g
O2: 350 g (mol/32 g)(7 mol/11 mol)(44.01 g/mol) = 306.3g theoretical yield
O2 is limiting reactant, thus 306.3 g.
Mass of CO2
in grams
C. (2 points) What is the % yield for this reaction?
(300.0 / 306.3) x 100% = 97.94% yield
% Yield
D. (5 points) How many grams of the excess reactant are present after the reaction is
complete?
(306.3 g)(mol/44.01 g)(1 mol/7 mol)(100.198 g/mol) = 99.62 g C7H16 (l) used
[or start with 300 g, ok!]
120.0 g – 99.62 g = 20.4 g remaining
Mass of Excess
Reagent
Exam I
Page 8 of 9
Exam I
Avogadro’s number = 6.022 x 1023 / mol
K = C + 273.15
M1 V 1 = M2 V 2
d = m/V
2.54 cm = 1.00 in (exact)
Page 9 of 9
F = 9/5 C + 32
Solubility Rules:
Compounds that are soluble or mostly soluble
• Group 1, NH4+, chlorates, acetates, nitrates
• Halides (except Pb2+, Ag+, and Hg22+)
• Sulfates (except Ca2+, Sr2+, Ba2+, Pb2+, and Hg22+)
Compounds that are insoluble
• Hydroxides, sulfides (except above rule, and group 2 sulfides)
• Carbonates, phosphates, chromates (except above rules)