Problem 88
Draw Lewis structures for the AsCl \(_{4}^{+}\) and \(\mathrm{AsCl}_{6}-\) ions. What type of reaction (acid-base, oxidation-reduction, or the like) is the following? $$ 2 \mathrm{AsCl}_{5}(g) \longrightarrow \mathrm{AsCl}_{4} \mathrm{As} \mathrm{Cl}_{6}(s) $$
Problem 89
There are two forms of solid sulfur: rhombic and monoclinic. The stable form of sulfur at \(25^{\circ} \mathrm{C}\) is the rhombic form. Upon heating, the rhombic form converts to the monoclinic form, which is the stable form of sulfur at high temperatures. Consider the process: $$ \mathrm{S}_{\text { rhombic }}(s) \longrightarrow \mathrm{S}_{\text { monoclinic }}(s) $$ Predict the signs of \(\Delta H\) and \(\Delta S\) for this process. Which form of sulfur has the more ordered structure (has the smaller positional probability)?
Problem 90
In large doses, selenium is toxic. However, in moderate intake, selenium is a physiologically important element. How is selenium physiologically important?
Problem 91
In the 1950 s and 1960 s, several nations conducted tests of nuclear warheads in the atmosphere. It was customary, following each test, to monitor the concentration of strontium- 90 (a radioactive isotope of strontium) in milk. Why would strontium- 90 tend to accumulate in milk?
Problem 93
Sulfur forms a wide variety of compounds in which it has \(+6\) \(+4,+2,0,\) and \(-2\) oxidation states. Give examples of sulfur compounds having each of these oxidation states.
Problem 95
Hydrogen gas is being considered as a fuel for automobiles. There are many chemical means for producing hydrogen gas from water. One of these reactions is $$ \mathrm{C}(s)+\mathrm{H}_{2} \mathrm{O}(g) \longrightarrow \mathrm{CO}(g)+\mathrm{H}_{2}(g) $$ In this case the form of carbon used is graphite. a. Calculate \(\Delta H^{\circ}\) and \(\Delta S^{\circ}\) for this reaction using data from Appendix \(4 .\) b. At what temperatures is this reaction spontaneous? Assume \(\Delta H^{\circ}\) and \(\Delta S^{\circ}\) do not depend on temperature.
Problem 96
Molten \(\mathrm{CaCl}_{2}\) is electrolyzed for 8.00 \(\mathrm{h}\) to produce \(\mathrm{Ca}(s)\) and \(\mathrm{Cl}_{2}(g) .\) a. What current is needed to produce 5.52 \(\mathrm{kg}\) of calcium metal? b. If 5.52 \(\mathrm{kg}\) calcium metal is produced, what mass (in kg) of \(\mathrm{Cl}_{2}\) is produced?
Problem 97
Calculate the solubility of \(\mathrm{Mg}(\mathrm{OH})_{2}\left(K_{\mathrm{sp}}=8.9 \times 10^{-12}\right)\) in an aqueous solution buffered at \(\mathrm{pH}=9.42 .\)
Problem 98
Which of the following statement(s) is(are) true? a. The alkali metals are found in the earth’s crust in the form of pure elements. b. Gallium has one of the highest melting points known for metals. c. When calcium metal reacts with water, one of the products is \(\mathrm{H}_{2}(g) .\) d. When AlCl \(_{3}\) is dissolved in water, it produces an acidic solution. e. Lithium reacts in the presence of excess oxygen gas to form lithium superoxide.
Problem 99
What is the hybridization of the underlined nitrogen atom in each of the following molecules or ions? a. \(\mathrm{NO}^{+}\) b. \(\mathrm{N}_{2} \mathrm{O}_{3}\left(\mathrm{O}_{2} \mathrm{NNO}\right)\) c. \(\mathrm{NO}_{2}^{-}\) d. \(\mathrm{N}_{2}\)
