Chapter 16 Text

eMedia Exercises 659
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In many reactions the addition of A1C13 produces the
same effect as the addition of H+. (a) Draw a Lewis structure
for A1C13 in which no atoms carry formal charges,
and determine its structure using the VSEPR method.
(b) What characteristic is notable about the structure in
part (a) that helps us understand the acidic character of
AlCls ? (c) Predict the result of the reaction between AIC13
and NH3 in a solvent that does not participate as a reactant.
(d) Which acid-base theory is most suitable for discussing
the similarities between A1C13 and H+?
[16 llll What is the boiling point of a 0.10 M solution of NaHSO4
if the solution has a density of 1.002 g/mL?
(16.1121 Cocaine is a weak organic base whose molecular formula
is CJ7H21NO4- An aqueous solution of cocaine was
found to have a pH of 8.53 and an osmotic pressure of
52.7 torr at 15QC. Calculate Kb for cocaine.
[16.1131 The iodate ion is reduced by sulfite according to the following
reaction:
lO5~(acj) + 3SO32~(aq)^r(ac]) + 3SO42~(fli7)
The rate of this reaction is found to be first order in IO3",
first order in SO32~, and first order in H+. (a) Write the
rate law for the reaction, (b) By what factor will the rate
of the reaction change if the pH is lowered from 5.00 to
3.50? Does the reaction proceed faster or slower at the
lower pH? (c) By using the concepts discussed in Section
14.6, explain how the reaction can be pH-dependent even
though H+ does not appear in the overall reaction.
[16.114] (a) Using dissociation constants from Appendix D, determine
the value for the equilibrium constant for each of
the following reactions. (Remember that when reactions
eMedia Exercises
^ 16.116 You can measure the pH in the Acids and Bases simulation
(eChapter 16.4) for aqueous solutions of 13 different
compounds, (a) List the compounds available in the simulation,
and identify each as a strong acid, a weak acid,
a strong base, or a weak base, (b) For each compound,
measure and record the pH of a 0.05 M solution.
16.117 (a) Using data from the Acids and Bases simulation
(eChapter 16.4), calculate the Ka of HNO2. (b) Determine
the percent ionization of HNO2 at 2.0 M, 0.20 M, 0.020 M,
and 0.0020 M concentrations, (c) Explain the trend in percent
ionization using Le Chatelier's principle.
16.118 The Introduction to Aqueous Acids animation (eChapter
36.5) illustrates the ionization in water of two different
strong acids and one weak acid, (a) Given that all
three ionize to produce hydrogen ion in water, what is it
about the behavior of the weak acid that makes it different
from the strong acids? (b) What is the consequence
of this difference in terms of pH?
«-119 The Introduction to Aqueous Bases animation (eChapter
16.5) illustrates the ionization of a weak base, (a) Write
are added, the corresponding equilibrium constants are
multiplied.)
(i)
(aq) + OH (acj) ^—- CO3 (aq) + HjOfZ)
NH3(«j)
(b) We usually use single arrows for reactions when the
forward reaction is appreciable (K much greater than I)
or when products escape from the system, so that equilibrium
is never established. If we follow this convention,
which of these equilibria might be written with a single
arrow?
[16.115] Lactic acid, CH3CH(OH)COOH, received its name
because it is present in sour milk as a product of bacterial
action. It is also responsible for the soreness in muscles
after vigorous exercise, (a) The pKa of lactic acid is 3.85.
Compare this with the value for propionic acid
(CH3CH2COOH, pKa = 4.89), and explain the difference,
(b) Calculate the lactate ion concentration in a
0.050 M solution of lactic acid, (c) When a solution of
sodium lactate, (CH3CH(OH)COO)Na, is mixed with
an aqueous copper(II) solution, it is possible, to obtain a
solid salt of copper(II) lactate as a blue-green hydrate,
(CH3CH(OH)COO)2Cu-xH2O. Elemental analysis of
the solid tells us that the solid is 22.9% Cu and 26.0% C
by mass. What is the value for x in the formula for
the hydrate? (d) The acid-dissociation constant for the
Cu (ag) ion is 1.0 X 10~8. Based on this value and
tbe acid-dissociation constant of lactic acid, predict
whether a solution of copper(II) lactate will be acidic,
basic, or neutral. Explain your answer.
the equation that corresponds to the ionization of ammof
nia in water, (b) In the animation the ammonia molecule
ionizes, producing aqueous hydroxide. What is it about
> the behavior of ammonia in water that makes ammonia