General Chemistry Principles, Patterns, and Applications, 2011

11. The general mechanism by which valinomycin functions is described in the text. If you were asked to develop
a new antibiotic that functions like valinomycin, what type of structural features would you want to
incorporate into it?
12. You have been asked to determine the concentrations of both Mg 2+ and Ca 2+ in a sample of hard water using
EDTA (ethylenediaminetetraacetic acid), which forms stable complexes with both metal ions. The procedure
requires two titrations. In the first, you adjust the pH of the water to about 10 by adding a solution of KOH.
You then add a small amount of an indicator that, by itself, is blue at pH 10 but which forms a red complex
with either Mg 2+ or Ca 2+ . Titrating the sample with a solution of EDTA will cause the solution to turn from red
to blue when all the metal ions have reacted with the EDTA. The second titration is identical to the
first, except that it is carried out at pH 13, and the volume of EDTA solution needed to reach the endpoint
is less than in the first titration. What is the difference between what is being measured in these two
titrations? Which titration measures the concentration of only a single metal ion? Identify that metal ion and
explain how the procedure described allows you to determine the concentrations ofboth Mg 2+ and Ca 2+ .
13. The primary component of ordinary glass is SiO 2 , which is difficult to work with due to its high melting point
(1700°C). Adding metal oxides lowers the melting temperature to a workable level (700–900°C) and causes
the liquid to flow more easily. Both Na 2 O and K 2 O are commonly used for this purpose. Which of these oxides
produces a glass that hardens more rapidly and at a higher temperature? Why is there a difference?
14. Lead poisoning can be treated by administering EDTA, an organic compound that binds to Pb 2+ (ETDA is
described in Problem 12), thereby removing lead from the system. If you are thinking of administering EDTA
as a clinical treatment for Ni 2+ poisoning because of its effectiveness in removing Pb 2+ , what additional factors
do you need to consider?
15. Silicon, aluminum, and oxygen, the most abundant constituents of Earth’s crust, are found in many minerals.
For example, two feldspars, which are typical components of granites, are albite and anorthite. Albite has the
composition Na[AlSi 3 O 8 ]; in anorthite, Al 3+ replaces one of the Si 4+ ions. Suggest a plausible cation in anorthite
in place of Na + .
16. When a plant root is immersed in an aqueous environment, its uptake of metal ions is dictated by equilibrium
considerations. Metal ions can be captured by reaction with various types of carrier molecules. The resulting
complexes can pass through the cell membrane and dissociate, thereby transporting the metal ions into the
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