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Chemistry 212
Key 5
Spring 2004
1. Which of the following is least likely to be colored?
a) Co3+
b) Cr3+
c) Fe3+
d) Mn2+
e) V5+
2. The reaction of CrBr3(H2O)5 with excess AgNO3 yields 1 mole of AgBr per mole of Cr. The
best representation of this compound is:
a) [Cr(H2O)5Br]Br2
b) [Cr(H2O)3Br2]Br•2H2O
c) [Cr(H2O)4Br]Br2•H2O
d) [Cr(H2O)2Br3]•3H2O
3. The formulae provided as answers to question 2, are examples of __________ isomers.
c) linkage
d) optical
a) coordination sphere
b) geometrical
e) stereo
4. Which of the following elements exhibits a maximum oxidation state of +7?
a) Ba
b) Be
c) Br
d) Co
e) O
f) Se
5. Which of the following elements exhibits forms π-bonds most readily?
a) Ba
b) Be
c) Br
d) Co
e) O
f) Se
6. What is the VSEPR geometry of SF4?
a) bent
b) octahedral
c) seesaw
d) square planar
e) trigonal bipyramidal
7. What mass of AgCl dissolves in 1.0 L of water? Ksp(AgCl) = 1.8 x 10-10
a) 2.6 x 10-8 g
b) 1.3 x 10-5 g
c) 1.9 x 10-3 g
d) 12 g
e) cannot determine from the information given
8. A certain chemical reaction has ∆H = -89 kJ/mol and ∆S = 55 J/mol•K. When does this
reaction proceed spontaneously?
a) The reaction is always spontaneous.
b) The reaction is spontaneous only at high temperatures.
c) The reaction is spontaneous only at low temperatures.
d) The reaction is never spontaneous.
Discussion questions
1. Define: (8 points)
complex – an assembly of a metal ion and bound Lewis bases
electronegativity – the tendency of bound atoms to attract electrons towards themselves
2. Consider the high spin molecule trans-[Fe(NH3)4Cl2]Cl. What is the electron configuration of
the Fe? Draw out the crystal field energy level diagram, show electron placement and label it.
Draw the complex ion. (14 points)
[Ar] 3d5
Cl
H3N
Fe
H3N
NH3
Cl
NH3
Cl
z2 ↑ ↑ x2-y2
↑ ↑ ↑
xy yz
xz
3. Describe how the d orbitals are split by ligands in a tetrahedral field. (8 points)
Assume a metal with 1 electron in its d-orbitals and 4 ligands an infinite distance away
centered between the coordinate axes in non-adjacent volumes (opposite corners on a cube).
At this point the 5 d-orbitals are degenerate and the electron spends an equal length of time in
each. As the ligands approach the metal, their lone pairs of electrons repel the metal delectron when it is in orbitals that point at the ligands (xy, xz, and yz). This raises the energy
of these orbitals relative to the energies of the orbitals pointing along the axes (z2 and x2-y2).
xy, xz, yz
xy
xz
yz
z2 x2-y2
∆
z2 x2-y2
4. Write a balanced equation for the reaction of sodium sulfide with hydrochloric acid? (5
points)
Na2S(aq) + 2 HCl(aq) → 2 NaCl(aq) + H2S(g)
5. Discuss the halogens. (5 points)
Each halogen is obtained by oxidation of the halide ion to the halogen in a molten salt, except
fluorine. None of the halogens is particularly abundant in nature, however all are easily
accessible in concentrated forms rendering this point moot. All halogens have high electron
affinities and ionization energies. Each is the highest of their respective period. All readily
form the –1 ion. All possess the highest electronegativities of their respective periods.
These properties, in conjunction with low X2 bond energies make these elements highly
reactive. Beginning with chlorine, all can form compounds with the halogen in a positive
oxidation state (+1, 3, 5, & 7). They all exist as colored diatomic molecules.
6.
Complete and balance these reactions: (8 points)
a) CaO(s) + H2O(l) → Ca(OH)2 (aq)
b) NaNH2 (s) + H2O(l) → NaOH(aq) + NH3(aq)
7. Provide formulas for silicon dioxide, potassium phosphide, sodium thiosulfate (central sulfur).
Give the oxidation state of the underlined atom for each. (12 points)
SiO2 (+4)
K3P (-3)
Na2S2O3 (+6)
8. In a certain oxidation state, copper behaves as if it were a main group element instead of a
transition metal. What oxidation state is that and why would you expect this to be observed.
(5 points)
Cu+, its electron configuration is [Ar] 4d10. This is the same as Zn2+ and leads to reactivity as
the alkaline earth metals.