Chemistry 5 Test 2
Name(printed): ___________________________________________________
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PERIODIC TABLE OF THE ELEMENTS
1A
1
H
8A
2
He
2A
4
Be
3A
5
B
4A
6
C
5A
7
N
6A
8
O
7A
9
F
4.003
3
Li
6.941
9.012
10.81
12.01
14.01
16.00
19.00
20.18
11
Na
12
Mg
5B
6B
7B
15
P
16
S
17
Cl
18
Ar
24.31
4B
14
Si
22.99
3B
13
Al
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
39.10
40.08
44.96
47.88
50.94
52.00
54.94
55.85
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
85.47
87.62
88.91
91.22
92.91
95.94
(98)
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
132.9
137.3
138.9
178.5
181.0
183.8
87
Fr
88
Ra
89
Ac
104
Rf
105
Db
106
Sg
(223)
226.0
227.0
(261)
(262)
58
Ce
59
Pr
140.1
90
Th
232.0
1.008
8B
10
Ne
1B
2B
26.98
28.09
30.97
32.07
35.45
39.95
28
Ni
29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
58.93
58.69
63.55
65.39
69.72
72.61
74.92
78.96
79.90
83.80
45
Rh
46
Pd
47
Ag
48
Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
101.1
102.9
106.4
107.9
112.4
114.8
118.7
121.8
127.6
126.9
131.3
76
Os
77
Ir
78
Pt
79
Au
80
Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
186.2
190.2
192.2
195.1
197.0
200.6
204.4
207.2
209.0
(209)
(210)
(222)
107
Bh
108
Hs
109
Mt
(263)
(264)
(265)
(268)
60
Nd
61
Pm
62
Sm
63
Eu
64
Gd
65
Tb
66
Dy
67
Ho
68
Er
69
Tm
70
Yb
71
Lu
140.9
144.2
(145)
150.4
152.0
157.3
158.9
162.5
164.9
167.3
168.9
173.0
175.0
91
Pa
92
U
93
Np
94
Pu
95
Am
96
Cm
97
Bk
98
Cf
99
Es
100
Fm
101
Md
102
No
103
Lr
231.0
238.0
237.0
(244)
(243)
(247)
(247)
(251)
(252)
(257)
(258)
(259)
(260)
metals
A few Constants
Avagadro’s Number, N = 6.022*1023 Gas constant, R = 0.08206 L atm/K mole, 1 L atm = 101.3 J
nonmetals
Name __________________________________________________________
PLEASE PRINT CLEARLY
1.
A volume of 10.0 mL of 0.10 M H3PO4 was titrated with 0.10 M NaOH. Part of the pH response to addition of
various amounts of NaOH is shown.
Points A to F identify the concentrations of
phosphoric acid and the various phosphoruscontaining anions formed from it during the
course of the titration. Please identify these
phosphor-containing species at either the set of
points A-E or the set B-F. Data extracted from
the graph are sufficient for this problem. Note,
this is an idealized graph.
4
points/part or 1 point/species
A)
[H3PO4] = 0.1M – 0.012M = 0.088M
[H2PO4-1]=0.012M
[HPO42-] = KA2 = 10-6M or essentially zero
[PO43-] = KA2KA3/[H+] = 10-6*2*10-11/0.012 =1.7*10-15M or essentially zero
B) 15mls of solution, containing
0.05moles of NaH2PO4 (0.05mol Na+ and 0.05mol H2PO4-) , Æ [H2PO-4] = 0.05*10/15 = =
0.033(3)M
[H3PO4] = 0.033(3)M
other ions essentially zero from part A
C) First equivalence point:
[H2PO-4] = 0.1*10/20 = 0.05M
[H3PO4] zero,
other ions essentially zero from A
D) titrating the second proton:
[H2PO-4] = 0.05*10/25 = 0.02M
[HPO2-4] = 0.02M
other ions and phosphoric acid zero or essentially zero
E) second eq. point:
[HPO2-4] = 0.1*10/30 = 0.033(3) M
other ions and phosphoric acid zero or essentially zero
F) titrating the 3rd proton:
[HPO2-4] = [PO3-4] = 0.05*10/35 = 0.014M
other ions and phosphoric acid zero or essentially zero
2.
A separation of 0.010 M manganese (II) from 0.010 M iron (III) is to be made by hydroxide precipitation.
Determine the pH range suitable for such a separation as follows:
a.
The lowest pH is that at which 99.9% of the iron (III) precipitates as iron (III) hydroxide.
b.
The highest pH is 0.10 unit below that at which manganese (II) hydroxide just precipitates.
KSP’s for the iron and manganese bases are respectively 6.3*10-38 and 2*10-13.
Fe(OH)3(S) ' Fe3+(aq)+ 3OH- (aq)
KSP = [Fe3+][OH-]3 ,
[OH-] = {6.3*10-38/1*10-5}1/3
[OH-] = 1.85*10-11
pOH = 10.73, pH = 3.27
Mn(OH)2 ' Mn2+ + 2OHKSP = [Mn2+][OH-]2 solving,
pOH = 5.35
pH = 8.65
∴ the pH range must be 3.27-8.55
3.
The heat liberated when one mole of ammonia is formed from the elements at 25 oC in a calorimeter
fitted with a piston which can move against the standard pressure of the atmosphere is 46.11 kJ. Find ∆E, ∆H,
q and w for the process.
1/2N2 + 3/2H2 ' NH3
∆E = q + w = q – P∆V, ∆H = ∆E + P∆V
∴ ∆H = ∆E – w = q = -46.11 kJ
w = -P∆V = -∆nRT = 2.48 kJ
∆H = q = -46.11 kJ
∆E = q + w = -43.63kJ
4.
The standard enthalpy of combustion of gaseous ethane (C2H6) is -1560 kJ-mole-1 at 25 oC. How
much heat is liberated when one mole of ethane is burned in a bomb calorimeter (∆V=0) at 25 oC? The
volume of liquid water produced in the reaction may be ignored.
C2H6(g) + 7/2O2(g) Æ 2CO2(g) + 3H2O(l)
∆H = -1560 kJ/mol
Since ∆V = 0, w = 0 and ∆H = q + ∆nRT (see last problem for proof),
q = ∆H – ∆nRT
q = -1560 kJ – (2-4.5)*8.3 J/mol-K * 298K = -1554 kJ -
5.
Determine ∆Hfo of gaseous nitrogen pentoxide (N2O5) given:
N2(g) + O2(g) Æ 2NO(g)
∆Ho = 180.5 kJ
2NO2(g) Æ 2NO + O2(g)
∆Ho = 114.1 kJ
2N2O5(g) Æ 4NO2(g) + O2(g)
∆Ho = 110.2 kJ
N2(g) + 5/2O2(g) Æ N2O5(g)
∆Hfo = ∆H1 + (-∆H2) + ½(-∆H3)
∆Hfo = 180.5kJ + (-114.1)kJ + (-55.1)kJ = 11.3 kJ