Chapter 19

Although the earth was formed from the same interstellar material as the sun, there is little elemental hydrogen \(\left(\mathrm{H}_{2}\right)\) in the earth's atmosphere. Explain.

List two major industrial uses of hydrogen.

How do the acidities of the aqueous solutions of the alkaline earth metal ions \(\left(\mathrm{M}^{2+}\right)\) change in going down the group?

Diagonal relationships in the periodic table exist as well as the vertical relationships. For example, Be and Al are similar in some of their properties as are \(\mathrm{B}\) and \(\mathrm{Si}\). Rationalize why these diagonal relationships hold for properties such as size, ionization energy, and electron affinity.

In most compounds, the solid phase is denser than the liquid phase. Why isn't this true for water?

What is nitrogen fixation? Give some examples of nitrogen fixation.

All the Group \(1 \mathrm{A}\) (1) and \(2 \mathrm{A}\) ( 2 ) metals are produced by electrolysis of molten salts. Why?

Why are the tin(IV) halides more volatile than the tin(II) halides?

Write balanced equations describing the reaction of lithium metal with each of the following: \(\mathrm{O}_{2}, \mathrm{S}, \mathrm{Cl}_{2}, \mathrm{P}_{4}, \mathrm{H}_{2}, \mathrm{H}_{2} \mathrm{O},\) and HCl.

The electrolysis of aqueous sodium chloride (brine) is an important industrial process for the production of chlorine and sodium hydroxide. In fact, this process is the second largest consumer of electricity in the United States, after the production of aluminum. Write a balanced equation for the electrolysis of aqueous sodium chloride (hydrogen gas is also produced).

Many lithium salts are hygroscopic (absorb water), but the corresponding salts of the other alkali metals are not. Why are lithium salts different from the others?

What will be the atomic number of the next alkali metal to be discovered? How would you expect the physical properties of the next alkali metal to compare with the properties of the other alkali metals summarized in Table 19-4?

One harmful effect of acid rain is the deterioration of structures and statues made of marble or limestone, both of which are essentially calcium carbonate. The reaction of calcium carbonate with sulfuric acid yields carbon dioxide, water, and calcium sulfate. Because calcium sulfate is marginally soluble in water, part of the object is washed away by the rain. Write a balanced chemical equation for the reaction of sulfuric acid with calcium carbonate.

Write balanced equations describing the reaction of Sr with each of the following: \(\mathrm{O}_{2}, \mathrm{S}, \mathrm{Cl}_{2}, \mathrm{P}_{4}, \mathrm{H}_{2}, \mathrm{H}_{2} \mathrm{O},\) and HCl.

What mass of barium is produced when molten \(\mathrm{BaCl}_{2}\) is electrolyzed by a current of \(2.50 \times 10^{5}\) A for \(6.00 \mathrm{h} ?\)

How long will it take to produce \(1.00 \times 10^{3} \mathrm{kg}\) of magnesium metal by the electrolysis of molten magnesium chloride using a current of \(5.00 \times 10^{4} \mathrm{A} ?\)

Beryllium shows some covalent characteristics in some of its compounds, unlike the other alkaline earth compounds. Give a possible explanation for this phenomenon.

What ions are found in hard water? What happens when water is "softened"?

Consider element \(113 .\) What is the expected electron configuration for element \(113 ?\) What oxidation states would be exhibited by element 113 in its compounds?

Thallium and indium form +1 and +3 oxidation states when in compounds. Predict the formulas of the possible compounds between thallium and oxygen and between indium and chlorine. Name the compounds.

Boron hydrides were once evaluated for possible use as rocket fuels. Complete and balance the following equation for the combustion of diborane. $$\mathbf{B}_{2} \mathrm{H}_{6}(g)+\mathbf{O}_{2}(g) \longrightarrow \mathbf{B}(\mathrm{OH})_{3}(s)$$

Elemental boron is produced by reduction of boron oxide with magnesium to give boron and magnesium oxide. Write a balanced equation for this reaction.

Write equations describing the reactions of Ga with each of the following: \(\mathrm{F}_{2}, \mathrm{O}_{2}, \mathrm{S},\) and HCl.

Write a balanced equation describing the reaction of aluminum metal with concentrated aqueous sodium hydroxide.

\(\mathrm{Al}_{2} \mathrm{O}_{3}\) is amphoteric. What does this mean?

Discuss the importance of the \(\mathrm{C}-\mathrm{C}\) and \(\mathrm{Si}-\mathrm{Si}\) bond strengths and of \(\pi\) bonding to the properties of carbon and silicon.

Besides the central atom, what are the differences between \(\mathrm{CO}_{2}\) and \(\mathrm{SiO}_{2} ?\)

Silicon is produced for the chemical and electronics industries by the following reactions. Give the balanced equation for each reaction. a. \(\mathrm{SiO}_{2}(s)+\mathrm{C}(s) \longrightarrow \mathrm{Si}(s)+\mathrm{CO}(g)\). b. Silicon tetrachloride is reacted with very pure magnesium, producing silicon and magnesium chloride. c. \(\mathrm{Na}_{2} \mathrm{SiF}_{6}(s)+\mathrm{Na}(s) \longrightarrow \mathrm{Si}(s)+\mathrm{NaF}(s)\).

Write equations describing the reactions of Sn with each of the following: \(\mathrm{Cl}_{2}, \mathrm{O}_{2},\) and HCl.

The compound \(\mathrm{Pb}_{3} \mathrm{O}_{4}\) (red lead) contains a mixture of lead(II) and lead(IV) oxidation states. What is the mole ratio of lead(II) to lead(IV) in \(\mathrm{Pb}_{3} \mathrm{O}_{4} ?\)

Tin forms compounds in the +2 and +4 oxidation states. Therefore, when tin reacts with fluorine, two products are possible. Write balanced equations for the production of the two tin halide compounds and name them.

The oxyanion of nitrogen in which it has the highest oxidation state is the nitrate ion \(\left(\mathrm{NO}_{3}^{-}\right) .\) The corresponding oxyanion of phosphorus is \(\mathrm{PO}_{4}^{3-} .\) The \(\mathrm{NO}_{4}^{3-}\) ion is known but not very stable. The \(\mathrm{PO}_{3}^{-}\) ion is not known. Account for these differences in terms of the bonding in the four anions.

In each of the following pairs of substances, one is stable and known, and the other is unstable. For each pair, choose the stable substance, and explain why the other is unstable. a. \(\mathrm{NF}_{5}\) or \(\mathrm{PF}_{5}\) b. \(\mathrm{AsF}_{5}\) or \(\mathrm{AsI}_{5}\) c. \(\mathrm{NF}_{3}\) or \(\mathrm{NBr}_{3}\)

Arsenic reacts with oxygen to form oxides that react with water in a manner analogous to that of the phosphorus oxides. Write balanced chemical equations describing the reaction of arsenic with oxygen and the reaction of the resulting oxide with water.

The Group \(5 \mathrm{A}\) (15) elements can form molecules or ions that involve three, five, or six covalent bonds; \(\mathrm{NH}_{3}, \mathrm{AsCl}_{5},\) and \(\mathrm{PF}_{6}^{-}\) are examples. Draw the Lewis structure for each of these substances, and predict the molecular structure and hybridization for each. Why doesn't \(\mathrm{NF}_{5}\) or \(\mathrm{NCl}_{6}^{-}\) form?

Compare the Lewis structures with the molecular orbital view of the bonding in \(\mathrm{NO}, \mathrm{NO}^{+},\) and \(\mathrm{NO}^{-} .\) Account for any discrepancies between the two models.

Many oxides of nitrogen have positive values for the standard free energy of formation. Using NO as an example, explain why this is the case.

In many natural waters, nitrogen and phosphorus are the least abundant nutrients available for plant life. Some waters that become polluted from agricultural runoff or municipal sewage become infested with algae. The algae flourish, and fish life dies off as a result. Describe how these events are chemically related.

Phosphate buffers are important in regulating the pH of intracellular fluids. If the concentration ratio of \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-} / \mathrm{HPO}_{4}^{2-}\) in a sample of intracellular fluid is \(1.1: 1,\) what is the \(p\) H of this sample of intracellular fluid? \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}(a q) \rightleftharpoons \mathrm{HPO}_{4}^{2-}(a q)+\mathrm{H}^{+}(a q) \quad K_{\mathrm{a}}=6.2 \times 10^{-8}\).

Phosphoric acid \(\left(\mathrm{H}_{3} \mathrm{PO}_{4}\right)\) is a triprotic acid, phosphorous acid \(\left(\mathrm{H}_{3} \mathrm{PO}_{3}\right)\) is a diprotic acid, and hypophosphorous acid \(\left(\mathrm{H}_{3} \mathrm{PO}_{2}\right)\) is a monoprotic acid. Explain this phenomenon.

Use bond energies to estimate the maximum wavelength of light that will cause the reaction $$\mathrm{O}_{3} \stackrel{h v}{\longrightarrow} \mathrm{O}_{2}+\mathrm{O}$$

Write a balanced equation describing the reduction of \(\mathrm{H}_{2} \mathrm{SeO}_{4}\) by \(\mathrm{SO}_{2}\) to produce selenium.

Complete and balance each of the following reactions. a. the reaction between sulfur dioxide gas and oxygen gas b. the reaction between sulfur trioxide gas and water c. the reaction between concentrated sulfuric acid and su\(\operatorname{crose}\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)\)

Ozone is desirable in the upper atmosphere but undesirable in the lower atmosphere. A dictionary states that ozone has the scent of a spring thunderstorm. How can these seemingly conflicting statements be reconciled in terms of the chemical properties of ozone?

How can the paramagnetism of \(\mathrm{O}_{2}\) be explained using the molecular orbital model?

Describe the bonding in \(\mathrm{SO}_{2}\) and \(\mathrm{SO}_{3}\) using the localized electron model (hybrid orbital theory). How would the molecular orbital model describe the \(\pi\) bonding in these two compounds?

Write the Lewis structure for \(\mathrm{O}_{2} \mathrm{F}_{2}\). Predict the bond angles and hybridization of the two central oxygen atoms. Assign oxidation states and formal charges to the atoms in \(\mathrm{O}_{2} \mathrm{F}_{2} .\) The compound \(\mathrm{O}_{2} \mathrm{F}_{2}\) is a vigorous and potent oxidizing and fluorinating agent. Are oxidation states or formal charges more useful in accounting for these properties of \(\mathrm{O}_{2} \mathrm{F}_{2} ?\)

Give the Lewis structure, molecular structure, and hybridization of the oxygen atom for OF \(_{2}\). Would you expect \(\mathrm{OF}_{2}\) to be a strong oxidizing agent like \(\mathrm{O}_{2} \mathrm{F}_{2}\) discussed in Exercise \(61 ?\)

Fluorine reacts with sulfur to form several different covalent compounds. Three of these compounds are \(\mathrm{SF}_{2}, \mathrm{SF}_{4},\) and \(\mathrm{SF}_{6}\) Draw the Lewis structures for these compounds, and predict the molecular structures (including bond angles). Would you expect OF \(_{4}\) to be a stable compound?

How does the oxyacid strength of the halogens vary as the number of oxygens in the formula increases?