Chapter 21

There has been some interest in the alkali metal fullerides, \(\mathrm{M}_{n} \mathrm{C}_{60}(\mathrm{s}),\) because at low temperatures, some of these compounds become superconducting. The alkali metal fullerides are ionic crystals comprising \(\mathrm{M}^{+}\) ions and \(\mathrm{C}_{60}^{n-}\) ions. The value of \(n\) can be deduced from the crystal structure. If \(M_{n} C_{60}\) consists of a cubic closest packed array of fulleride ions, with \(\mathrm{M}^{+}\) ions occupying all the octahedral and tetrahedral holes in the fulleride lattice, then what is the value of \(n\) and what is the empirical formula of the fulleride?

Mono Lake in eastern California is a rather unusual salt lake. The lake has no outlets; water leaves only by evaporation. The rate of evaporation is great enough that the lake level would be lowered by three meters per year if not for fresh water entering through underwater springs and streams originating in the nearby Sierra Nevada mountains. The principal salts in the lake are the chlorides, bicarbonates, and sulfates of sodium. An approximate "recipe" for simulating the lake water is to dissolve 18 tablespoons of sodium bicarbonate, 10 tablespoons of sodium chloride, and 8 teaspoons of Epsom salt (magnesium sulfate heptahydrate) in 4.5 liters of water (although the lake water actually contains only trace amounts of magnesium ion). Assume that 1 tablespoon of any of the salts weighs about \(10 \mathrm{g} .(1 \text { tablespoon }=3\) teaspoons.) (a) Expressed as grams of salt per liter, what is the approximate salinity of Mono Lake? How does this salinity compare with seawater, which is approximately 0.438 M NaCl and 0.0512 M MgCl_? (b) Estimate an approximate pH for Mono Lake water. How does your estimate compare with the observed \(\mathrm{pH}\) of about \(9.8 ?\) Actually, the recipe for the lake water also calls for a pinch of borax. How would its presence affect the pH? [Borax is a sodium salt, \(\mathrm{Na}_{2} \mathrm{B}_{4} \mathrm{O}_{7} \cdot 10 \mathrm{H}_{2} \mathrm{O},\) related to the weak monoprotic boric acid \(\left(\mathrm{pK}_{\mathrm{a}}=9.25\right) \cdot\) (c) Mono Lake has some unusual limestone formations called \(t u f\). They form at the site of underwater springs and grow only underwater, although some project above water, having formed at a time when the lake level was higher. Explain how the tufa form. [Hint: What chemical reaction(s) is(are) involved?]

In your own words, define the following terms: (a) dimer; (b) adduct; (c) calcination; (d) amphoteric oxide; (e) three-center two-electron bond.

Briefly describe each of the following ideas, methods, or phenomena: (a) diagonal relationship; (b) preparation of deionized water by ion exchange; (c) thermite reaction; (d) inert pair effect.

Explain the important distinction between each pair of terms: (a) peroxide and superoxide; (b) quicklime and slaked lime; (c) soap and detergent; (d) silicate and silicone; (e) sol and gel.

Of the following oxides, the one with the highest melting point is (a) \(\mathrm{Li}_{2} \mathrm{O} ;\) (b) \(\mathrm{BaO} ;\) (c) \(\mathrm{MgO} ;\) (d) \(\mathrm{SiO}_{2}.\)

The best oxidizing agent of the following oxides is (a) \(\mathrm{Li}_{2} \mathrm{O} ;(\mathrm{b}) \mathrm{MgO} ;(\mathrm{c}) \mathrm{Al}_{2} \mathrm{O}_{3} ;(\mathrm{d}) \mathrm{CO}_{2} ;(\mathrm{e}) \mathrm{SnO}_{2} ;(\mathrm{f}) \mathrm{PbO}_{2}.\)

Predict the products of the following reactions: (a) \(\mathrm{BCl}_{3}(\mathrm{g})+\mathrm{NH}_{3}(\mathrm{g})\) (b) \(\mathrm{K}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g})\) (c) \(\mathrm{Li}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g})\) (d) \(\mathrm{BaO}_{2}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(1)\)

Listed are several pairs of substances. For some pairs, one or both members of the pair react individually with water to produce a gas. For others, neither member of the pair reacts with water. The pair for which each member reacts with water and yields the same gaseous product is (a) \(\mathrm{Al}(\mathrm{s})\) and \(\mathrm{Ba}(\mathrm{s}) ;\) (b) \(\mathrm{Ca}(\mathrm{s})\) and \(\mathrm{CaH}_{2}(\mathrm{s}) ; \quad(\mathrm{c}) \quad \mathrm{Na}(\mathrm{s})\) and \(\mathrm{Na}_{2} \mathrm{O}_{2}(\mathrm{s}) ; \quad\) (d) \(\mathrm{K}(\mathrm{s})\) and \(\mathrm{KO}_{2}(\mathrm{s}) ;(\mathrm{e}) \mathrm{NaHCO}_{3}(\mathrm{s})\) and \(\mathrm{HCl}(\mathrm{aq}).\)

Complete and balance the following. Write the simplest equation possible. If no reaction occurs, so state. (a) \(\operatorname{Li}_{2} \mathrm{CO}_{3}(\mathrm{s}) \stackrel{\Delta}{\longrightarrow}\) (b) \(\mathrm{CaCO}_{3}(\mathrm{s})+\mathrm{HCl}(\mathrm{aq}) \longrightarrow\) (c) \(\mathrm{Al}(\mathrm{s})+\mathrm{NaOH}(\mathrm{aq}) \longrightarrow\) (d) \(\operatorname{BaO}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(1) \longrightarrow\) (e) \(\mathrm{Na}_{2} \mathrm{O}_{2}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{g}) \longrightarrow\)

Assuming that water, common reagents (acids, bases, salts), and simple laboratory equipment are available, give a practical method to prepare (a) \(\mathrm{MgCl}_{2}\) from \(\mathrm{MgCO}_{3}(\mathrm{s}) ;\) (b) \(\mathrm{NaAl}(\mathrm{OH})_{4}\) from \(\mathrm{Na}(\mathrm{s})\) and \(\mathrm{Al}(\mathrm{s}) ;\) and (c) \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) from \(\mathrm{NaCl}(\mathrm{s}).\)

Write the simplest chemical equation to represent the reaction of (a) \(\mathrm{K}_{2} \mathrm{CO}_{3}\left(\text { aq) and } \mathrm{Ba}(\mathrm{OH})_{2}(\mathrm{aq})\right.\); (b) \(\operatorname{Mg}\left(\mathrm{HCO}_{3}\right)_{2}(\) aq) on heating; (c) tin(II) oxide when heated with carbon; (d) \(\mathrm{CaF}_{2}(\mathrm{s})\) and \(\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{concd}\) aq); (e) \(\mathrm{NaHCO}_{3}(\mathrm{s})\) and \(\mathrm{HCl}(\mathrm{aq}) ;\) (f) \(\mathrm{PbO}_{2}(\mathrm{s})\) and HBr(aq); and (g) the reduction of \(\mathrm{SiF}_{4}\) to pure \(\mathrm{Si},\) by using Na as the reducing agent.

Write an equation to represent the reaction of gypsum, \(\mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O},\) with ammonium carbonate to produce ammonium sulfate (a fertilizer), calcium carbonate, and water.

Write chemical equations to represent the most probable outcome in each of the following. If no reaction is likely to occur, so state. (a) \(\mathrm{B}(\mathrm{OH})_{3} \stackrel{\Delta}{\longrightarrow}\) (b) \(\mathrm{Al}_{2} \mathrm{O}_{3}(\mathrm{s}) \stackrel{\Delta}{\longrightarrow}\) (c) \(\mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}(\mathrm{s}) \stackrel{\Delta}{\longrightarrow}\)

A chemical dictionary gives the following descriptions of the production of some compounds. Write plausible chemical equations based on these descriptions. (a) lead(II) carbonate: adding a solution of sodium bicarbonate to a solution of lead nitrate. (b) lithium carbonate: reaction of lithium oxide with ammonium carbonate solution. (c) hydrogen peroxide: by the action of dilute sulfuric acid on barium peroxide. (d) lead(IV) oxide: action of an alkaline solution of calcium hypochlorite on lead(II) oxide.

Name the chemical compound(s) you would expect to be the primary constituent(s) of (a) stalactites; (b) gypsum; (c) "barium milkshake"; (d) blue sapphires.