59. (Transition metal complexes,
Le Châtelier's principle) The cobalt complexes participating in the
equilibrium below comprise a humidity sensor. From Le Châtelier's
principle, when the sensor is moist (excess H2O), what color
is the cobalt complex?
60. (Equilibrium, polarity)
Demonstration: A solution of iodine dissolved in water is placed in a separatory
funnel. An equal volume of CCl4 is to be added to the funnel.
Based on polarity,
most of the iodine will prefer to stay in the water layer, most of
the iodine will prefer to transfer into the CCl4 layer
Add the CCl4 in such a way as to minimize mixing. Is the system
Shake several times to show that color changes eventually cease.
The equilibrium constant K for the reaction
I2 (in water) = I2 (in CCl4)
has a value of ~100 near room temperature. If at some time the concentration
of I2 in water is 0.1 mM and of I2 in CCl4
is 1.0 mM, what will happen?
no net movement of I2 between solvents, I2
in water will move into CCl4 , I2 in CCl4 will
move into water.
Once equilibrium for this partitioning experiment has been established,
the amount of each solvent is to be doubled. What will then happen?
no net movement of I2 between solvents, I2
in water will move into hexane, I2 in hexane will move into
Repeat the initial experiment in the reverse order: a solution of CCl4
having the same total I2 concentration is placed in a separatory
funnel and an equal volume of water is to be added to it.
Will the I2 partition itself in the same way after shaking? (Compare
the two separatory funnel color distributions)
In water, I2 can combine with I­p; ion to form a complex,
I3­p;, with a relatively large equilibrium constant of ~1000 M-1. Demonstration:
If KI is added to the water layer containing I2 that had come
to equilibrium with a layer of I2 in CCl4 , what will
no net movement of I2 between solvents, I2 in
water will move into CCl4 , I2 in CCl4
will move into water
61. (Equilibrium) Consider
the bonds that must be made or broken for the reaction
O2N-NO2 (g) = 2 NO2 (g)
The reaction will be
63. (Equilibrium, concentration,
competition) A competition experiment involves O2 and CO vying
for hemoglobin (Hb) sites, defined by the equilibrium
Hb(O2)4 + 4 CO = Hb(CO)4 + 4O2
From Le Châtelier's principle, how is CO poisoning reversed?
decrease O2 pressure, increase O2 pressure,
64. (Equilibrium, Le Châtelier's
principle; Ch. 5 & 9 "Companion") The body-centered cubic
(bcc) phase of a metal has a 68% packing efficiency, while the face-centered
cubic (fcc) phase of the same metal has a 74% packing efficiency. For the
bcc metal = fcc metal
as pressure increases, the equilibrium
shifts to the left, shifts to the right, is unaffected
66. (Enthalpy, equilibrium)
N2(g) + 3H2(g) = 2 NH3(g) + reaction energy;
Which are collectively stronger bonds?
those in the reactants, those in the products
What effect will spraying H2O into the system have if NH3
is far more soluble in H2O than N2 and H2?
no effect, increase product, increase reactants
68. (pH scale) A solution with pH=5 is 100 times more
acidic than a solution with a pH = ?
7, 3, 0.05
70. (Weak acids, Le Châtelier's
principle) CH3COOH = CH3COO- + H+; pKa=5
To make more CH3COOH, add
To make more CH3COO-, add
At pH=2, what is the most prevalent species?
CH3COOH, CH3COO-, equal amounts of the
acid and its conjugate base
At pH=5, what is the most prevalent species?
CH3COOH, CH3COO-, equal amounts of the acid
and its conjugate base
Which plot shows the correct distribution of acetic acid as a function of
83. (Doping, semiconductors, periodic properties; Ch.
8 "Companion") Which dopant will act as an acceptor for Si?
B, Ge, As
As a donor?
B, Ge, As
84. (Equilibrium; Ch. 8 "Companion")
As a dopant in Si, Al is involved in the equilibrium
Al = h+ + Alx. What is the charge on the aluminum in the product?
-1, 0, +1
85. (Phase changes, Le Châtelier's principle; Ch.
9 "Companion") Nickel titanium memory metal has a symmetric cubic
unit cell in its high temperature form and a less symmetric noncubic unit
cell in its low temperature form. Demonstration 9.6 "Companion":
By slightly changing the Ni to Ti ratio, a sample can have, at room temperature,
one or the other of these phases. Two small rods, one in the symmetric structure,
one in the less symmetric structure at room temperature are dropped on the
floor. One produces a ringing sound, the other a soft thud. Which gives
the ringing sound?
the symmetric high temperature phase, the less symmetric low
To cause the ring-sounding sample to give a thudding sound,
heat it, cool it
Demonstration: cool the sample with liquid nitrogen, remove it and drop
it to hear a thud. Rapid hand warming will eventually restore the ring during
Which phase is more mechanically flexible?
the symmetric high temperature phase, the less symmetric low temperature
When nickel titanium memory metal interconverts between the symmetric high
temperature form and the less symmetric low temperature form, which of the
elemental analysis, X-ray diffraction pattern, hardness
When a sample of nickel-titanium in the high temperature phase is bent,
as pictured, the atoms that are under compression and thus favored by Le
Châtelier's principle to convert to the denser low-temperature phase
at the bottom of the bend, in the middle of the bend, at the
top of the bend
Demonstration 9.5 "Companion": Bend memory metal eyeglass
frames and show that they return to their original shape. Then cool with
liquid nitrogen to show that when the eyeglass frames are in the more flexible
low temperature phase they stay bent until they return to room temperature,
where they regain their original shape.
86. (Semiconductors, bands;
Ch.8 "Companion") Pictured below is an energy band diagram for
When doped into Si, Al is a(n)
When doped into Si, P is a(n)
Which energy level corresponds to Al?
Which energy level corresponds to P?
87. (Semiconductors, doping;
Ch 8 "Companion") Which is a weaker acceptor (analogous to weaker
Which is a weaker donor (analogous to weaker base)?
98. (Equilibrium) Keq = [NO2]2/[N2O4];
heat + N2O4 = 2 NO2
As temperature increases, the equilibrium constant, K
increases, decreases, remains constant
99. (Autoionization, equilibrium;
Ch. 8 "Companion") If the product of n and p in a semiconductor
is a constant, the two are
directly related, inversely related
100. (pH scale) Demonstration:
Predict a pH value for 0.1 M NaOH.
1, 7, 13
102. (Doping, equilibrium,
autoionization; Ch. 8 "Companion") KSi = [h+]x[e-] = p x n = 1020
cm­p;6 For this endothermic autoionization reaction, as temperature increases,
increases, decreases, remains constant
116. (Equilibrium) If K =
100 = [I2 in CCl4] / [I2 in water] for
I2 in water = I2 in CCl4
What is K for the reverse reaction, I2 in CCl4 = I2
100, 1, 0.01
121. (Coordination chemistry,
equilibrium) Demonstration: A green solution of Ni(H2O)62+
has added to it a small quantity of ammonia, which turns the solution blue
through formation of Ni(NH3)62+; the value
of K for this reaction is ~109. To this blue solution is added
about the same number of moles of the chelating ligand ethylenediamine (en),
turning the solution violet through formation of Ni(en)32+;
the value of K for this reaction is also ~109. Using these same
quantities, what happens if en is added first, then the ammonia is added?
the violet solution turns blue; the violet solution stays violet
122. (Vapor pressure, equilibrium)
Demonstration: The same amount of solid iodine is added to two identical
glass tubes, which are then stoppered and heated to the same temperature.
The color in the two tubes is seen to be the same and solid iodine is still
present in the bottom of the tubes. When a lot of additional iodine crystals
are added to one of the tubes
the color of the vapor in that tube will become darker, there is
no change in the color of the vapor, the color of the vapor in that
tube will become lighter
124. (Equilibrium, semiconductors,
doping; Ch. 8 "Companion;" LeChâtelier's principle) When
doped into Si, Cu is a weak acceptor, Cu = Cu- + h+.
To convert most of the copper to Cu-, dope with
a strong acceptor like aluminum, a strong donor like phosphorus
126. (Chromatography, equilibrium)
The chromatographic equilibrium for a species A can be described as A in
mobile phase <==> A in stationary phase
A mixture of two volatile compounds is injected onto a column with air,
which doesn't interact with the column. Which of the three peaks below is
1, 2, 3
Which of the other two peaks corresponds to the larger equilibrium constant
1, 2, 3
139. (Semiconductors, equilibrium,
Ch. 8 "Companion") When a semiconductor having autoionization
equilibrium constant K is irradiated with light above its band gap energy
n x p = K, n x p > K, n x p < K
147. (Semiconductors, equilibrium;
Ch. 8 "Companion") Given that the band gap energy for Ge is less
than that for Si, at room temperature what will be true of the equilibrium
constants for autoionization of the two solids?
KSi > KGe, KSi = KGe, KSi < KGe
148. (Semiconductors, equilibrium;
Ch. 8 "Companion") Compare the number of carriers per cm3 in silicon
and water at room temperature from the graph below?
104 times more in silicon, equal numbers, 104
times more in water
150. (Semiconductors; Ch.
8 "Companion") Conductivity reflects the concentration of electrons,
n, and holes, p; and n x p = K. In pure Si, K = 1020 cm-6.
There are approximately how many charge carriers per cm3?
1020, 1010, 10
When Si is doped with Al to make p = 1017, there are now approximately
how many charge carriers per cm3?
156. (Equilibrium) I2
in water = I2 in oil; K1 = [I2 in oil ] / [I2
I2 in oil = I2 in ether; K2 = [I2 in ether
] / [I2 in oil].
What is K3 for the summed reaction, I2 in water = I2
in ether; K3 = [I2 in ether] / [I2 in water]
K3 = K1 + K2, K3 = K1 x K2 , K3 = K1 / K2 , K3 = K2 / K1
157. (Chirality) Chiral molecules
rotate the plane of polarized light because the left- and right-hand circularly
polarized components of the light (which trace out chiral opposite-handed
helices) experience different refractive indices in their interactions with
a chiral molecule and travel at different velocities (c/n), causing a net
rotation of the plane-polarized light. If RHCPL travels faster through a
solution of the d isomer of a chiral molecule, causing a clockwise
rotation, which other combination causes the light to travel at this same
d isomer with LHCPL, l isomer with LHCPL,
l isomer with RHCPL
Is the plane of polarized light rotated in the same direction in both
of these experiments?
More questions are needed for this section. Please submit contributions