122H, Chemistry Section 1 Exam 3, S08
Don't forget to: Use Pencil and SHOW YOUR WORK CLEARLY in the spaces provided. Use UNIT ANALYSIS and ROUND the final answer to the correct number of SIGNIFICANT FIGURES. You MUST use the ICE method to do all equilibrium calculations. FAILURE TO DO THIS MAY RESULT IN REDUCED OR ZERO CREDIT. Please keep your eyes on your own paper and your answers covered. Use paper handed out for scratch paper. I will not grade anything on this paper. Turn in the entire exam when you are done. GOOD LUCK !!
USEFUL INFORMATION
Compound
CH4(g) CO2(g) NO(g) H2O(g) H2O(l) NH3(g)
Br2(g) BrF3(g) F2(g)
(kJ/mol) 75 394 91 242 286 46 31 256 82
Hf0
S0
(J/mol K) 186 214 211 189 70. 192 245 292 203 274
Average Bond Enthalpies (kJ/mol) HH CC C=C OO O=O O-H C-O C=O CO C-H 436 391 161 139 495 463 351 728 1072 413 Magnesium Lead Graphite Methanol Water
Csp (J/g0) 1.02 0.159 0.711 2.55 4.184
NOBr(g)
h= c= 1 mole = R= F=
6.626 x 10-34 J sec/photon 2.998 x 108 m/sec 6.02 x 1023 things 0.0821 L atm/mol K = 8.314 J/mol K 96,500 Coulomb/mol e
1m= 1 Hz = 1 mile = 1 atm = 1 kg = 1 cal =
109 nm 1 sec-1 5280 ft 760 mm Hg 2.20 lb 4.184 J
C + 273 = K 1 Volt = 1 Joule/Coulomb 1 ampere = 1 Coulomb/sec
o
PERIODIC TABLE OF THE ELEMENTS
1A
1
2A
3B
4B
5B
6B
7B
8B
8B
8B
1B
2B
3A
4A
5A
6A
7A
8A
2
H
4
He
4.003
1.008
3
Li
6.939
Be
9.012
5
B
6
C
7
N P
8
O S
9
F
10
Ne
20.18
10.81
12.01
14.01
16.00
19.00
11
Na
22.99
12
Mg
24.31
13
Al
26.98
14
Si
28.09
15
16
17
Cl
35.45
18
Ar
39.95
30.97
32.07
19
K
20
Ca
40.08
21
Sc
44.96
22
Ti
47.90
23
V
24
Cr
52.00
25
Mn
54.94
26
Fe
55.85
27
Co
58.93
28
Ni
58.71
29
Cu
63.55
30
Zn
65.39
31
Ga
69.72
32
Ge
72.61
33
As
74.92
34
Se
78.96
35
Br
79.90
36
Kr
83.80
39.10
50.94
37
Rb
85.47
38
Sr
87.62
39
Y
40
Zr
91.22
41
Nb
92.91
42
Mo
95.94
43
Tc
(99)
44
Ru
101.1
45
Rh
102.9
46
Pd
106.4
47
Ag
107.9
48
Cd
112.4
49
In
114.8
50
Sn
118.7
51
Sb
121.8
52
Te
127.6
53
I
54
Xe
131.3
88.91
126.9
55
Cs
132.9
56
Ba
137.3
57
La
138.9
72
Hf
178.5
73
Ta
181.0
74
W
75
Re
186.2
76
Os
190.2
77
Ir
192.2
78
Pt
195.1
79
Au
197.0
80
Hg
200.6
81
Tl
204.4
82
Pb
207.2
83
Bi
209.0
84
Po
(209)
85
At
(210)
86
Rn
(222)
183.8
87
Fr
(223)
88
Ra
226.0
89
Ac
227.0
104
105
106
107
108
109
Unq
(261)
Unp
(262)
Unh
(263)
Uns
(262)
Uno
(265)
Une
(266)
Equations PV = nRT t1/2 = ln 2/k t1/2 = [A]0/2k t1/2 = 1/[A]0k [A] = [A]0ekt = (1/2)n [A] = kt + [A]0 ln [A] = kt + ln [A]0 1/[A] = kt + 1/[A] 0 k = AeEa/RT ln k = (Ea/R)(1/T) + ln A ln (k2/k1) = (Ea/R)(1/T2 1/T1) n = t/t1/2 q = m Csp T qsys = qwater + qcalorimeter H = E + PV H = E + PV H = qp H0rxn = niH0f(prod) niH0f(react) Hrxn (react) (prod) q = n Hphase Suniverse = Ssystem + Ssurroundings Ssurroundings = Hsystem/T Sphase = Hphase /Tphase Srxn = niS(prod) niS(react) Euniverse = Esystem + Esurroundings = 0 E = q + w E = qv w = Pext V G = H TS G = H TS = TSuniverse at .... ? G0rxn = niG0f(prod) niG0f(react) G = G+ RT ln Q = RT ln (Q/K) Ecell = Eox + Ered G0 = nFE0cell G = nFEcell Ecell = Ecell (RT/nF) lnQ Kw = [H3O+][OH] = 1.0 x 1014 Ka(acid) Kb(conj base) = Kw pX = logX G = RTln K ln K = Hrxn/RT + Srxn/R ln (K2/K1) = (Hrxn/R)(1/T2 1/T1) Kp = Kc(RT)ngas ax2 + bx + c = 0 x = (b (b2 4ac)1/2 )/2a
Pb2+(aq) + 2e
Pb(s)
0.126
Pyridinium ion
C5 H5 NH+
5.6 x 106
C5 H5NH
FIRST NAME________________________ Exam 3, S08
LAST NAME________________________ PLEASE USE PENCIL !!!
1. (3 pts) Sudsy shampoo has a pH of 9.00 while Frothy shampoo has a pH of 3.00. Sudsy shampoo is ___________ times more
(FILL IN THE BLANK)
ACIDIC
(CIRCLE ONE)
BASIC
than Frothy.
2. (2 pts) Can nickel metal be oxidized by chlorine gas ? B. Can mercury metal reduce chloride ion ?
YES YES
NO NO
3. (4 pts) Blood plasma has a pH of approximately 7.4. What conjugate pairs could you use to create a buffer in this range ? A. Acid _______________________ Base _______________________
B. What is the pH of this system when the concentrations of acid and base are equal ? (Show your work)
4. (3 pts) In class we saw that distilled water is
NEUTRAL
SLIGHTLY ACIDIC
(CIRCLE ONE)
SLIGHTLY BASIC .
B. Write a balanced chemical equation to explain this.
5. (3 pts) What concentration nitric of acid is needed to give an aqueous solution with a pH of 1.33 ?
Exam 3, S08
Page 2
6. (20 pts) A standard voltaic cell is constructed with Cu2+(aq)/Cu(s) and Cr2O72(aq)/Cr3+(aq) half cell compartments connected by a sodium chloride salt bridge at 298 K. An inert platinum electrode is used in the chromium compartment. A. Write the equation for the spontaneous cell reaction.
B. Ecell0 for this cell is ________ V. The number of electrons transferred in this reaction is _________ C. In this reaction _________ is REDUCED FROM OXIDATION STATE ____ TO OXIDATION STATE ____ D. The REDUCING AGENT is ______________ E. Represent this cell using cell notation (such as Ag(s) | Ag+(1 M) || ...)
G. Sketch a picture of the cell and label all of the important features.
Exam 3, S08
Page 3
7. (8 pts) A solution contains 0.035M sodium benzoate, NaC6H5CO2 and 0.044 M of benzoic acid, C6H5COOH. Calculate the approximate pH of this solution after the addition of 0.015M of sodium hydroxide. (Assume that the volume remains constant, ICE)
B. What is the maximum amount of hydrochloric acid that can be added to the original solution before a large pH change occurs ?
8. (7 pts) In class I passed around a gold leaf. The gold was put onto the leaf as a result of: a.) Galvanizing b.) Electroplating c.) Anodizing
(circle one)
B. What current is required to deposit 25 grams of gold onto a leaf from an aqueous solution of gold chloride in 20 minutes ? (Hint: See useful information)
Exam 3, S08
Page 4
9. (6 pts) Pyridine, C5H5N, is a colorless liquid with a disagreeable odor and sharp taste. It is also a useful organic solvent that dissolves in water. An aqueous solution of pyridine is 0.025 M. There are two unique ways to convert this solution above into a buffer. To illustrate each method choose two reagents and indicate how much of each you would add to one liter of solution in order to create a pyridine buffer. (ASSUME THAT THE VOLUME REMAINS CONSTANT AS EACH SUBSTANCE IS ADDED.) A. _______________ moles of ______________ B. _______________ moles of ______________
10. (8 pts) A standard voltaic cell is constructed with Hg2+(aq)|Hg(l) and Cl2(g)|Cl (aq) half cell compartments connected by a salt bridge. A. Calculate the equilibrium constant for the reaction at 298 K.
B. Write the expression for calculating the cell potential at standard pressure (1 atm) when the concentration of Hg2+(aq) is 0.050M, and Cl(aq) is 0.010M. You do not need to do this calculation.
Exam 3, S08
Page 5
11. (3 pts) A Lewis acid
ACCEPTS
DONATES
CIRCLE ONE
FILL IN THE BLANK
__________________ .
12. (2 pts) The conjugate base of NH3 is ______________________. 13. (13 pts) In class I demonstrated that an aqueous solution of sodium bicarbonate is
ACIDIC NEUTRAL BASIC
(CIRCLE ONE)
Assume that you have a 0.10 M solution of sodium bicarbonate. B. Calculate the approximate pH of this solution, first assuming that bicarbonate acts as an acid in water.
C. Now calculate the approximate pH of this solution assuming that bicarbonate acts as a base in water.
D. Do your calculations support your answer in part A ? Explain
Exam 3, S08
Page 6
14. (8 pts) Indicate whether each of the following compounds will give an acidic A, basic B, or neutral N, solution when dissolved in water. Write the hydrolysis reaction for any with a pH different than 7.
(HINT: SEE USEFUL INFORMTION)
Hydrolysis Reaction
A B N
Sodium sulfite
A
B
N
Iron(III) iodide
A
B
N
Calcium nitrate
15. (3 pts) A reducing agent
ACCEPTS
DONATES
CIRCLE ONE
__________________ .
FILL IN THE BLANK
16. (4 pts) An aqueous solution of potassium iodide is electrolyzed using two platinum (inert) electrodes.
A. Two possible products can form at the cathode. They are: (circle two) K(s) I2 (s) I (aq) O2(g) K+ (aq) H2(g) H2O(l)
B. Two possible products can form at the anode. They are: (circle two) K(s) I2 (s) I (aq) O2(g) K+ (aq) H2(g) H2O(l)
C. Now decide which product is correct for each: Anode product ___________ Cathode product _____________
17. (3 pts) Consider the acids: Formic acid (HCOOH), nitrous acid, and hydrofluoric acid.
A. The formula for the strongest conjugate base is _________________ B. If formic acid is combined with fluoride ion you would predict the reaction to be:
PRODUCT REACTANT
(CIRCLE ONE)
favored at equilibrium.