Last Name: _____________________________ First Name: _______________
Lab Sec. # ____
TA: ____________________ Lab day/time: _____________
Bryan Enderle, Ph.D.
CHEMISTRY 2A
Final Exam – Winter 2007
Multiple Choice
Circle one
Instructions:
CLOSED BOOK EXAM! DO NOT OPEN the exam until instructed to do so.
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. A scientific
calculator may be used (if it is a programmable calculator, its memory must
be cleared before the exam). Sharing of calculators is not allowed.
(1)
(2)
Read each question carefully (22 problems, 10 pages).
ANSWER ALL THE QUESTIONS YOU ARE SURE OF FIRST, AND
THEN USE THE REMAINING TIME FOR THE REST.
Please show all relevant work where it is indicated for full credit.
The last page contains a periodic table and some useful information.
You may remove it for easy access.
If you finish early, RECHECK YOUR ANSWERS!
(3)
(4)
(5)
U.C. Davis is an Honor Institution
Possible Points
# 1-11
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
1-11 total points:
(3 points each)
/ 33
12.
a
b
c
d
e
# 12-15 (5 points each)
/ 20
13.
a
b
c
d
e
# 16
(15 points)
/ 15
14.
a
b
c
d
e
# 17
(10 points)
/ 10
15.
a
b
c
d
e
# 18
(06 points)
/ 06
# 19
(03 points)
/ 03
# 20
(11 points)
/ 11
# 21
(04 points)
/ 04
# 22
(10 points)
/ 10
Total Score (112)
/ 112
12-15 total points:
WINTER 2007
FINAL CHEM 2A
(Page 2 of 10)
Concepts: Multiple Choice
Questions 1-11: 3 points each (no partial credit)
1.
If
a.
b.
c.
d.
e.
one heats up a gas at constant volume:
pressure increases
# of moles increases
molecules slow down
pressure decreases
the gas explodes
2.
Which element that is positively ionized one time has the following
configuration: 1s2 2s2 2p6 3s2 3p6?
a) Na
b) Ne
c) Ca
d) K
e) Ba
3.
The bond in Cl2 and LiF is, respectively:
a) covalent, ionic
b) ionic, covalent
c) ionic, ionic
d) covalent, covalent
e) polar covalent, ionic
4.
Choose the INCORRECT name formula combination.
a. Fe2O3 iron (III) oxide
b. H2SO3 sulfurous acid
c. SiO2 silicon oxide
d. NH4ClO3 ammonium chlorate
e. CaH2 calcium hydride
5.
Write the net ionic equation for the reaction of magnesium carbonate and
nitric acid.
a. MgCO3(s) + 2 H+ Æ Mg2+ + H2O + CO2(g)
b. MgCO3(s) + 2 HNO3(aq) Æ Mg(NO3)2 + H2O + CO2(g)
c. MgCO3(s) + 2 HNO3(aq) Æ Mg(NO3)2(aq) + H2CO3(aq)
d. Mg2+ + CO32- + 2 H+ Æ Mg2+ + H2O + CO2(g)
e. no reaction
WINTER 2007
6.
FINAL CHEM 2A
(Page 3 of 10)
The quantum numbers of the last electron of arsenic COULD be:
a.
n = 4, l = 2, ml = 1, ms = 1/2
b.
n = 4, l = 1, ml = 1, ms = 1/2
c.
d.
e.
n = 3, l = 1, ml = 1, ms = 1/2
n = 4, l = 3, ml = 1, ms = 1/2
n = 4, l = 1, ml = 1/2, ms = 0
7.
Which of the following statements is NOT true?
a. The atomic radius decreases from left to right through a period of
elements.
b. Cations are larger than the atoms from which they are formed.
c. The metallic character of elements decreases from left to right through a
period of elements.
d. The ionization energy increases from left to right through a period of
elements.
e. The atomic radius increases down the periodic table.
8.
If the formula of an oxide is X2O3, what is the formula of the chloride of X?
a. XCl
b. X3Cl
c. XCl3
d. XCl6
e. X2Cl3
9.
In which of he following molecules would you expect the nitrogen to nitrogen
bond to be the shortest?
a. N2H4
b. N2O4
c. N2O
d. NH3
e. N2
10.
Which combination of hybrid orbital descriptions and electronic geometry
descriptions is INCORRECT?
a. sp/linear
b. sp2/trigonal planar
c. sp3/tetrahedral
d. sp3d/square planar
e. sp3d2/octahedral
11.
How many σ bonds and how many π bonds are present in the carbonic acid
molecule, H2CO3?
a. 2 σ /4 π
b. 3 σ /3 π
c. 4 σ /2 π
d. 5 σ /1 π
e. 6 σ /0 π
WINTER 2007
FINAL CHEM 2A
(Page 4 of 10)
Calculations: Multiple Choice
Questions 12-15: 5 points each (no partial credit)
12.
What is the mass in grams of 1 atom of sulfur (atomic mass = 32.066 amu)?
a. 5.325 x 10-23 b. 1.931 x 10-25 c. 1.661 x 10-24 d. 5.179 x 10-26
13.
A 5.00 mL sample of a nitric acid solution is titrated with 33.5 mL of 0.201 M
NaOH. What is the molarity of the nitric acid solution?
a. 0.0300 M
b. 0.149 M
c. 1.35 M
d. 6.7 M
e. 0.522 M
14.
What is the mass of 2.00 L of C3H6 when measured at STP?
a. 1.88 g
b. 1.88 Kg
c. 3.75 g
d. 3.75 mg
e. 2.00 g
15. What is the wavelength associated with electrons traveling at 1/10 the speed
of light ?
a) 2.42x10-11 m
b) 0.242 sec-1
c) 3.00 x 108 m sec -1
d) 3.42 x 1011 m
e) 2.42 sec-1
m = 9.109 X 10-31 Kg
c = 3.00 X 108 m s-1
h = 6.626 X 10-34 Kg m2 s-1
u = c/10 Æ λ = 2.42x10-11 m
WINTER 2007
16.
Molecule
ClF3
FINAL CHEM 2A
(Page 5 of 10)
(15 points) Fill in the following table (see ClF3 example):
Electron-Group
Geometry
Trigonal-Bipyramidal
Molecular Geometry
Ideal Bond
Hybridization
Polar or Nonpolar
Angles
(center atom)
T-shaped
90º
polar
sp3d
BeCl2
Linear
Linear
180º
Non-polar
sp
CH4
Tetrahedral
Tetrahedral
109.5º
Non-polar
sp3
OH2
Tetrahedral
Bent
109.5º
Polar
sp3
Non-polar
sp3d
PCl5
Trigonal-Bipyramidal Trigonal-Bipyramidal 90º, 120º
SF6
Octahedral
Octahedral
90º
Non-polar
sp3d2
XeF4
Octahedral
Square Planar
90º
Non-polar
sp3d2
WINTER 2007
FINAL CHEM 2A
(Page 6 of 10)
Partial Credit. Show ALL Your Work. Explain.
17.
(10 points) Combustion of 0.2000 g of a carbon, hydrogen, oxygen compound
yields 0.2998 g CO2 and 0.08190 g water.
(a) What is the percent composition of C, H and O?
(b) What is the empirical formula of this compound?
(c) Is this an inorganic or an organic compound?
(d) The molar mass of the compound is 176.13 amu. What is its chemical
formula?
(a) Percent Composition of C, H and O.
Compute moles of C per 0.2998 g of CO2: 0.2998/44.01 = 0.00681208 mol
Convert to g: 0.00681208*12.011 = 0.08181999 g
Compute moles of H per 0.08190 g of water: (0.08190/18.02)*2 = 0.0090899 mol
Convert to g: 0.0090899*1.008 = 0.0091626 g
Obtain mass of O in 0.20 g sample: 0.2000 – (0. 08181999 + 0. 0091626)=0.109018 g
Convert to moles: 0.109018/15.994 = 0.00681618
%C = (0. 08181999/0.2000) * 100 = 40.91%
%H = (0. 0091626/0.2000) * 100 = 4.581%
%O = (0. 109018/0.2000) * 100 = 54.51%
%C = 40.91
%H = 4.581
%O = 54.51
(b) Empirical Formula
Empirical formula C 0.00681208 H 0.0090899 O 0.00681618
Divide each subscript by the smallest and
multiply all of them by 3 to make them
integer numbers Î empirical formula C3H4O3.
(c) Inorganic or Organic Compound?
Organic
Empirical formula
C3H4O3
Organic
(d) Chemical Formula
Molar mass of C3H4O3 would be approx. 12*3 + 4 + 48 = 88. ==> ½ of the given molar
mass Î Chemical formula is C6H8O6 (vitamin C or ascorbic acid).
Chemical formula
C6H8O6
WINTER 2007
FINAL CHEM 2A
(Page 7 of 10)
18. (6 points) Dissolve 15.0 ml pure ethanol C2H5OH (density = 0.789 g/mL) in
enough water to produce 250.0 mL solution.
(a) What’s the molarity of ethanol in the solution?
(b) What is the name of the resulting hydrocarbon if you replace the OH
group of ethanol with a hydrogen atom?
(c) Is ethanol a base in solution?
(d) If we had propanol instead of ethanol and we assumed the same density,
would the molarity be smaller or bigger than that of the solution with
ethanol? Explain.
(a) Molarity
Determine how many moles are in solution:
15.0 x 0.789 [mL x g/mL] = 15.0 x 0.789 g = 11.8 g
Convert g to mole;
Molar mass is (2x12.01) + (6x1.008) + (1x16.00) = 46.07 g / mol Î
11.8 /46.07 mol = 0.256 mol of ethanol in 250 mL solution.
Apply definition of molarity
M = (mol solutes) / (liters of solution)
M = 0.256/0.2500 = 1.02
Molarity = 1.02
(b) Name of hydrocarbon
Ethane
(c) Is ethanol a base in solution?
No
(d) Smaller or bigger molarity?
Propanol has a molar mass larger than ethanol, hence the # of moles in
250mL solution is smaller than in the case of ethanol, and hence molarity is
smaller.
Smaller
WINTER 2007
FINAL CHEM 2A
(Page 8 of 10)
19. (3 points) What are the aluminum and sulfate ion concentrations in
0.0165 M Al2(SO4)3(aq)? What is the oxidation state of the metal ion?
Balanced equation Al2(SO4)3 (s) Æ 2Al3+(aq) + 3 SO42- (aq)
[Al3+] = 0.0165 x (2/1) = 0.0330 mol/L
[SO42-] = 0.0165 x (3/1) = 0.0495 mol/L
[Al3+] = 0.0330 M
[SO42-] = 0.0495 M
Oxidation state of metal ion = +3
20. (11 points) Write the symbol and electronic configuration of the:
(a) 3rd row alkali metal.
Na: 1s2 2s2 2p6 3s1
(b) 4th row alkaline earth metal.
Ca: 1s2 2s2 2p6 3s2 3p6 4s2
(c) 2nd row halogen.
F: 1s2 2s2 2p5
(d) Element in IVA group and in the fifth row.
Sn: [Kr] 5s2 4d10 5p2
(e) Which of the elements of group IVA have d electrons in their electronic
configurations?
Ge, Sn and Pb
WINTER 2007
21.
FINAL CHEM 2A
(4 points)
(Page 9 of 10)
Consider the Lewis structure of the triatomic anion:
[ P = Si = X ]
-
If you know that element X belongs to the third period of the periodic
table, which element is X? Show your work. Explain why.
Formal charge for P atom = -1
Formal charge for Si atom = 0
Assume formal charge for X atom = y
(-1) + (0) + (y) = -1 therefore y = 0. The Lewis structure thus indicates that
X atom has 6 electrons in its outer shell. X element belongs to the VIA
group, and because it also belongs to the third period, it is the element of
sulfur.
Sulfur
(10 points) Complete the MO energy level diagram for O2 2-.
a.
Fill in the electrons using arrows (↑ and/or ↓) for the atomic and
molecular orbitals.
b.
Designate all the energy levels (i.e., σ2s*, π2p, σ2s, etc.)
c.
Calculate the bond order for O2 2-.
d.
Is O2 2- a paramagnetic or diamagnetic chemical species?
22.
σ2p*
↑↓
↑↓
π2p*
↑↓
↑↓
↑
↑↓
2p
↑↓
π2p
↑↓
E
↑↓
2s
2s
↑↓
Bond order for O2
=
1
2p
σ2s*
↑↓
2-
↑↓
σ2p
↑↓
c.
↑↓
↑
d.
σ2s
Paramagnetic or Diamagnetic?
Circle ONE
WINTER 2007
FINAL CHEM 2A
(Page 10 of 10)
Periodic Table
Solubility rules:
Compounds which are soluble or mostly soluble:
•
Group 1, NH4+, chlorates, acetates, nitrates
•
Halides (except Pb2+, Ag+, and Hg22+)
•
Sulfates (except Sr2+, Ba2+, Pb2+, and Hg22+)
Compounds which are insoluble:
•
•
Hydroxides, sulfides (except above rule, and sulfides of group 2)
Carbonates, phosphates, chromates (except above rules)
Some useful equations and data:
PLEASE NOTE: Important values and equations required for calculations are given with
the respective problem. The following may or may not be of any use.
λ=
h
mυ
d=
PM
RT
Molarity =
Moles
Liter
n (moles) =
mass (g)
molar mass (g/mol)
PV = nRT
NA = 6.022 x 1023
h = 6.626x10-34 Js
1 J = 1 kg m2 s-2 = 1 N m
mL·M = mmol
Ptotal = P1 + P2 + …
TK = ToC + 273.15
R = 0.082 L atm mol-1 K1
1 nm = 10-9 m
c = 3.00 x 108 m s-1
c = νλ
xA = nA / ntot = PA / Ptot
Ephoton = hν
Rate2/Rate1=(M1/M2)1/2
1 atm = 760 mmHg
∆E = RH(1/ni2 – 1/nf2)
me = 9.109387x10-28 g
∆ p = m ∆υ
d=
m
V
% Yield =
Actual Yield
Theoretica l Yield
x100