Download Exam 3

Name ______Mr. Perfect______________________________________ Date ____F 16_____________
1. Balance the following redox reactions using the half-reaction method. (10 pts)
a.
Cr + NO3- → Cr3+ + NO
[acidic]
Cr → Cr3+ + 3e3e- + 4H+ + NO3- → NO + 2H2O
4H+ + Cr + NO3- → Cr3+ + NO + 2H2O
b.
CrO42- + SO32- → Cr(OH)3 + SO42-
[basic]
2 x (3e- + 5H+ + CrO42- → Cr(OH)3 + H2O)
3 x (H2O + SO32- → SO42- + 2H+ + 2e-)
10H+ + 2CrO42- + 3H2O + 3SO32- → 2Cr(OH)3 + 2H2O + 3SO42- + 6H+
4 10H+ + 2CrO42- + 3H2O + 3SO32- → 2Cr(OH)3 + 2H2O + 3SO42- + 6H+
4OH4OH2CrO42- + 5H2O + 3SO32- → 2Cr(OH)3 + 3SO42- + 4OH2. Calculate Ecell and ΔG for the following voltaic cell under non-standard conditions: [Cu2+] =
0.10 M and [Zn2+] = 1.90 M. (10 pts)
Cu2+(aq) + Zn(s) → Cu(s) + Zn2+(aq)
Nernst Equation
0.0592 𝑉
°
𝐸𝑐𝑒𝑙𝑙 = 𝐸𝑐𝑒𝑙𝑙
−
𝑙𝑜𝑔𝑄
𝑛
F = 96500 J/Vmol
Standard Reduction Potentials
E°
2+
2e- + Cu → Cu
0.342 V
2+
2e- + Zn → Zn -0.762 V
E°cell = Ecat – Ean = 0.342 V – (-0.762 V) = 1.104 V
°
𝐸𝑐𝑒𝑙𝑙 = 𝐸𝑐𝑒𝑙𝑙
−
0.0592 𝑉
0.0592 𝑉
(1.9)
𝑙𝑜𝑔𝑄 = 1.104 𝑉 −
𝑙𝑜𝑔
= 𝟏. 𝟎𝟔𝟔 𝑽
𝑛
2
(0.1)
ΔG = -nFE = -(2 mol e-)(96500 J/V mol)(1.066 V) = -205767 J or -205.8 kJ
Chemistry 102 Exam 3
Name ______Mr. Perfect______________________________________ Date ____F 16_____________
3. Complete the following nuclear reactions. Clearly state the nuclear decay mode to receive full
credit. (10 pts)
Negatron Emission
Electron Capture
97
60
0
0
a) 27 Co  1 e + 60
b) 43Tc + −10𝑒  97
28𝑁𝑖
42 Mo + 0𝛾
c)
226
88
Alpha Particle Decay
Ra  42 He + 222
86𝑅𝑛
Positron Emission
d)
Bi  01 e + 205
82𝑃𝑏
205
83
4. Using the spectrochemical series, fill the electrons in the following crystal field diagram for
the following diamagnetic transition metal complex. Is this the ligand a strong field ligand or a
weak field ligand? Also predict if the compound is square planar or tetrahedral. (10 pts)
Spectrochemical Series
I <Br <Cl <F <OH-<H2O//<NH3<en< NO2-<CN-<CO
Weak Field ligands (High Spin)
Strong Field Ligands (Low Spin)
Tetrahedral
Square Planar
-
-
-
-
[Ni(CO)4]2+
CO gives low spin = strong field
Ni2+
d8 ion
__↑↓__ ___↑__ __↑___
dxy
dyz
dxz
_____
dx2-y2
__↑↓__
dxy
__↑↓__
dz2
__↑↓__ __↑↓__
dz2
dx2-y2
Paramagnetic
__↑↓__ __↑↓__
dxz
dyz
Compound is Square planar.
Diamagnetic
5. Using the short-hand notation (Noble Gas Configuration), write the ground-state electron
configuration for the following transition metals: (10 pts)
a. Fe2+
b. Re7+
c. Cu1+
d. Pd2+
[Ar]3d6
[Xe]4f14
[Ar]3d10
[Kr]4d8
Chemistry 102 Exam 3
Name ______Mr. Perfect______________________________________ Date ____F 16_____________
6. Draw the following transition metal complexes in their correct molecular geometry and state
the hybrid orbital involved in the bonding. Name the molecular geometry shape and label the
bond angles to receive full credit. (10 pts)
* Some of the charges and ligands and metals may be incorrect due to the drawing program used.
a) FeCl3
b) K3[Fe(CN)6]
N
C
N
N
C
C
4-
Cl
Fe
N
Cl
C
C
-
Fe
C
Cl
N
N
Trigonal Planar
Octahedral
2
sp
sp3d2
all bond angles are 120°
all bond angles are 90°
7. Draw the isomers for the following compounds: (10 pts)
a. Optical Isomers
Co(en)2Cl2
NH
NH Cl
4-
Cl
Co
NH
NH
b. Coordination Isomers
[Fe(H2O)5Cl]Br
HN
NH
4-
HO
Co
Cl
Cl
HN
NH
OH Cl
4-
HO
Fe
HO
OH
OH Br
4-
Fe
OH
HO
OH
OH
mirror images
8. State the oxidation number and coordination number of the following transition metals for
each of the following compounds: (10 pts)
a) K4[PtCl6]
b) [Cu(NH3)4]SO4
Oxidation Number = +2
Oxidation Number = +2
Coordination Number = 6
Coordination Number = 4
c) [Co(H2O)6]I3
d) K2[CoCl4]
Oxidation Number = +3
Oxidation Number = +2
Coordination Number = 6
Coordination Number = 4
Chemistry 102 Exam 3
Name ______Mr. Perfect______________________________________ Date ____F 16_____________
9. The complex ion [Ti(H2O)6]3+ is violet in solution. Calculate the crystal field splitting energy
in kJ/mol for this ion. (10 pts)
h = 6.626 x 10-34 Js
c = 3.00 x 108 m/s
Absorbed wavelength (nm) Observed Color
6.02 x 1023 ions/mol
400 violet
greenish-yellow
450 blue
yellow
1 nm = 10-9 m
490 blue-green
red
570 yellow-green
violet
580 yellow
dark-blue
600 orange
blue
650 red
green
3.00𝑥108 𝑚
(6.626𝑥10−34 𝐽 𝑠)(
) 6.02𝑥1023 𝑖𝑜𝑛/𝑚𝑜𝑙
ℎ𝑐
𝑠
∆=𝐸 =
=
×
= 𝟐𝟏𝟎 𝒌𝑱/𝒎𝒐𝒍
10−9 𝑚
𝜆
1000 𝐽/𝑘𝐽
(570 𝑛𝑚)(
)
𝑛𝑚
10. Write a partial decay series for Ra-226 undergoing the following sequential decays. (10pts)
Alpha → Alpha → negatron → alpha
Alpha Decay
226
4
222
88𝑅𝑎 → 2𝐻𝑒 + 86𝑅𝑛
Alpha Decay
→ 42𝐻𝑒 + 218
84𝑃𝑜
222
86𝑅𝑛
Negatron Emission
→ −10𝑒 + 218
85𝐴𝑡
218
84𝑃𝑜
218
85𝐴𝑡
Alpha Decay
→ 42𝐻𝑒 + 214
83𝐵𝑖
11. Extra Credit. The following solutions of nickel absorb light in the following regions of the
electromagnetic spectrum: NiCl42-(702 nm) and NiBr42-(756 nm). Which ion has the greater
crystal field splitting energy? (5 pts)
ℎ𝑐
𝐶𝑟𝑦𝑠𝑡𝑎𝑙 𝐹𝑖𝑒𝑙𝑑 𝑆𝑝𝑙𝑖𝑡𝑡𝑖𝑛𝑔 𝐸𝑛𝑒𝑟𝑔𝑦 = ∆= 𝐸 =
𝜆
E702 nm > E756 nm
Chemistry 102 Exam 3