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21.6 End-of-Chapter Material

Application Problems

  1. For each application, which of the indicated substances would you select and why? Base your selections on the properties and reactivities of the alkaline earth metals and their compounds.

    1. source of CO2 at low temperature—BeCO3 or CaCO3
    2. window material for x-ray tubes—beryllium or strontium
    3. source of iodide ions in aqueous solution—BaI2 or BeI2
    4. formation of a stable organometallic compound by reacting a metal with an alkyl halide—calcium or magnesium
    5. synthesis of refractory materials—magnesium oxide or barium oxide
  2. Ultrahigh-purity tritium, which is needed in the nuclear weapons industry, is obtained by allowing a mixture of tritium and its nuclear decay product, helium-3, to diffuse through a thin block of palladium metal. Explain why this is an effective method for separating the two substances.

  3. In one technique for harnessing solar energy, the blue-green algae Anabaena cylindrica is used to produce H2 and O2 photosynthetically. The resulting gases are collected, passed through palladium metal, and then recombined in a fuel cell to produce electricity. Draw a diagram showing how this process might work.

  4. Scientists speculate that sodium atoms react with atmospheric ozone to produce a high-energy species, which is then reduced by atomic oxygen. This process is believed to occur as meteors enter Earth’s atmosphere. Write equations for these reactions. Is sodium regenerated in this process?

  5. Propose an effective compound for purifying and regenerating air for breathing in a submarine and justify your choice.

  6. Explain why administering cryptands to a person suffering from iron toxicity could be an effective clinical treatment.

  7. Calcium magnesium carbonate [CaMg(CO3)2], also known as dolomite, is a primary constituent of soils. It is formed when water containing magnesium ions comes in contact with calcium carbonate. Do you expect dolomite to be more or less resistant to acid rain than calcium carbonate? Why?

  8. Few classes of reagents have proved to be as useful for organic syntheses as the Grignard reagents (RMgX), which are produced by reacting an organohalogen compound (RX) with magnesium in an ether solvent. The ease of formation of a Grignard reagent depends on the structure of the organohalogen compound.

    1. For a given R group, arrange the alkyl halides (RX) in order of decreasing reactivity with Mg and justify your reasoning.
    2. Is it possible to make a Grignard reagent using an organosodium compound and MgCl2? Why or why not?
    3. Is MgCl2 or MgI2 preferable for the reaction described in part (b)?
  9. The percentage of the population that developed leukemia in the vicinity of the Chernobyl nuclear reactor rose substantially after the nuclear accident in 1986. Why? Based on information in this chapter, what might have been done to reduce the incidence of leukemia in children who lived in the affected region?

  10. Explain how ingesting large amounts of NaCl could induce a heart attack.

  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 Mg2+ and Ca2+ 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 Mg2+ or Ca2+. 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 of both Mg2+ and Ca2+.

  13. The primary component of ordinary glass is SiO2, 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 Na2O and K2O 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 Pb2+ (ETDA is described in Problem 12), thereby removing lead from the system. If you are thinking of administering EDTA as a clinical treatment for Ni2+ poisoning because of its effectiveness in removing Pb2+, 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[AlSi3O8]; in anorthite, Al3+ replaces one of the Si4+ 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 cell. The Na+, K+, Mg2+, and Ca2+ ions are all transported using this mechanism. Which of these ions would be captured by

    1. oxygen donors with a neutral or low (−1) charge?
    2. carboxylates, phosphates, and some neutral oxygen donors?
    3. polyphosphates with a total negative charge greater than −2?
    4. nitrogen donors?
  17. Sodium carbonate has long been used in the glass industry, for making water softeners, and in the wood pulp and paper industries. Recently, sodium carbonate has proved useful for removing SO2 and H2SO4 from the flue gases of coal- and oil-fired power stations. Write balanced chemical equations showing the reactions that occur when flue gases are passed through solid sodium carbonate.

  18. Hard water contains high concentrations of Ca2+ and Mg2+. These ions react with soaps (sodium and potassium salts of naturally occurring carboxylic acids) to form an insoluble scum. Explain how adding Na2CO3 to hard water can soften the water and improve the ability of soaps to remove dirt and grime.

  19. Do you expect MgCO3 or Mg(OH)2 to be more soluble in water? Based on your answer, explain how adding Ca(OH)2 softens water by removing Mg2+. Be sure to show a balanced chemical equation for the reaction.

  20. How does a low-sodium diet help lower blood pressure? Do you think a diet high in KCl would also be effective at lowering blood pressure? Explain your answer.

Answers

    1. BeCO3; less stable to decomposition due to small size of Be2+
    2. Be; low Z results in little absorption of x-rays
    3. BaI2; has greater ionic character
    4. Mg; smaller size results in stronger polar covalent bonds to carbon
    5. MgO; higher lattice energy and melting point
  1. KO2; the reaction is 4KO2(s) + 4CO2(g) + 2H2O(g) → 4KHCO3(s) + 3O2(g).

  2. Dolomite will be less resistant to acid rain because MgCO3 is more soluble than CaCO3.

  3. Restrict milk consumption and supplement diet with calcium to minimize the uptake of strontium.

  4. The glass containing sodium will have a higher softening or melting temperature because the smaller sodium ions will link the silicate chains more strongly.

  5. Ca2+

  6. Na2CO3(s) + SO2(g) → Na2SO3(s) + CO2(g); Na2CO3(s) + H2SO4(g) → Na2SO4(s) + CO2(g) + H2O(g)