Chapter 22

Write a chemical formula for each compound or ion, and indicate the oxidation state of the group \(5 \mathrm{~A}\) element in each formula: (a) phosphate ion, (b) arsenous acid, (c) antimony(III) sulfide, (d) calcium dihydrogen phosphate, (e) potassium phosphide, (f) gallium arsenide.

Account for the following observations: (a) Phosphorus forms a pentachloride, but nitrogen does not. (b) \(\mathrm{H}_{3} \mathrm{PO}_{2}\) is a monoprotic acid. (c) Phosphonium salts, such as \(\mathrm{PH}_{4} \mathrm{Cl}\), can be formed under anhydrous conditions, but they can't be made in aqueous solution. (d) White phosphorus is more reactive than red phosphorus.

Account for the following observations: (a) \(\mathrm{H}_{3} \mathrm{PO}_{3}\) is a diprotic acid. (b) Nitric acid is a strong acid, whereas phosphoric acid is weak. (c) Phosphate rock is ineffective as a phosphate fertilizer. (d) Phosphorus does not exist at room temperature as diatomic molecules, but nitrogen does. (e) Solutions of \(\mathrm{Na}_{3} \mathrm{PO}_{4}\) are quite basic.

Write a balanced equation for each of the following reactions: (a) preparation of white phosphorus from calcium phosphate, (b) hydrolysis of \(\mathrm{PBr}_{3},(\mathrm{c})\) reduction of \(\mathrm{PBr}_{3}\) to \(\mathrm{P}_{4}\) in the gas phase, \(\mathrm{using} \mathrm{H}_{2}\)

Give the chemical formula for (a) hydrocyanic acid, (b) nickel tetracarbonyl, (c) barium bicarbonate, (d) calcium acetylide (e) potassium carbonate.

Give the chemical formula for (a) carbonic acid, (b) sodium cyanide, (c) potassium hydrogen carbonate, (d) acetylene, (e) iron pentacarbonyl.

Complete and balance the following equations: (a) \(\mathrm{ZnCO}_{3}(s) \stackrel{\Delta}{\longrightarrow}\) (b) \(\mathrm{BaC}_{2}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\) (c) \(\mathrm{C}_{2} \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow\) (d) \(\mathrm{CS}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow\) (e) \(\mathrm{Ca}(\mathrm{CN})_{2}(s)+\mathrm{HBr}(a q) \longrightarrow\)

Complete and balance the following equations: (a) \(\mathrm{CO}_{2}(g)+\mathrm{OH}^{-}(a q) \longrightarrow\) (b) \(\mathrm{NaHCO}_{3}(s)+\mathrm{H}^{+}(a q) \longrightarrow\) (c) \(\mathrm{CaO}(s)+\mathrm{C}(s) \stackrel{\Delta}{\longrightarrow}\) (d) \(\mathrm{C}(s)+\mathrm{H}_{2} \mathrm{O}(g) \stackrel{\Delta}{\longrightarrow}\) (e) \(\mathrm{CuO}(s)+\mathrm{CO}(g) \longrightarrow\)

Write a balanced equation for each of the following reactions: (a) Hydrogen cyanide is formed commercially by passing a mixture of methane, ammonia, and air over a catalyst at \(800^{\circ} \mathrm{C}\). Water is a by- product of the reaction. (b) Baking soda reacts with acids to produce carbon dioxide gas. (c) When barium carbonate reacts in air with sulfur dioxide, barium sulfate and carbon dioxide form.

Write a balanced equation for each of the following reactions: (a) Burning magnesium metal in a carbon dioxide atmosphere reduces the \(\mathrm{CO}_{2}\) to carbon. (b) In photosynthesis, solar energy is used to produce glucose \(\left(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\right)\) and \(\mathrm{O}_{2}\) from carbon dioxide and water. (c) When carbonate salts dissolve in water, they produce basic solutions.

Write the formulas for the following compounds, and indicate the oxidation state of the group \(4 \mathrm{~A}\) element or of boron in each: (a) boric acid, (b) silicon tetrabromide, (c) lead(II) chloride, (d) sodium tetraborate decahydrate (borax), (e) boric oxide, (f) germanium dioxide.

(a) How does the structure of diborane \(\left(\mathrm{B}_{2} \mathrm{H}_{6}\right)\) differ from that of ethane \(\left(\mathrm{C}_{2} \mathrm{H}_{6}\right) ?\) (b) Explain why diborane adopts the geometry that it does. (c) What is the significance of the statement that the hydrogen atoms in diborane are described as "hydridic'?

Write a balanced equation for each of the following reactions: (a) Diborane reacts with water to form boric acid and molecular hydrogen. (b) Upon heating, boric acid undergoes a condensation reaction to form tetraboric acid. (c) Boron oxide dissolves in water to give a solution of boric acid.

In your own words, define the following terms: (a) allotrope, (b) disproportionation, (c) interhalogen, (d) acidic anhydride, (e) condensation reaction, (f) protium.

Although the \(\mathrm{ClO}_{4}^{-}\) and \(\mathrm{IO}_{4}^{-}\) ions have been known for a long time, \(\mathrm{BrO}_{4}^{-}\) was not synthesized until \(1965 .\) The ion was synthesized by oxidizing the bromate ion with xenon difluoride, producing xenon, hydrofluoric acid, and the perbromate ion. (a) Write the balanced equation for this reaction. (b) What are the oxidation states of \(\mathrm{Br}\) in the Br-containing species in this reaction?

Write a balanced equation for the reaction of each of the following compounds with water: (a) \(\mathrm{SO}_{2}(g)\) (b) \(\mathrm{Cl}_{2} \mathrm{O}_{7}(g),(\mathrm{c})\) \(\mathrm{Na}_{2} \mathrm{O}_{2}(s),(\mathbf{d}) \mathrm{BaC}_{2}(s)\) (e) \(\mathrm{RbO}_{2}(s),\) (f) \(\mathrm{Mg}_{3} \mathrm{~N}_{2}(s),(\mathrm{g}) \mathrm{NaH}(s)\)

What is the anhydride for each of the following acids: (a) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (b) \(\mathrm{HClO}_{3}\) (c) \(\mathrm{HNO}_{2}\), (d) \(\mathrm{H}_{2} \mathrm{CO}_{3},\) (e) \(\mathrm{H}_{3} \mathrm{PO}_{4} ?\)

Explain why \(\mathrm{SO}_{2}\) can be used as a reducing agent but \(\mathrm{SO}_{3}\) cannot.

A sulfuric acid plant produces a considerable amount of heat. This heat is used to generate electricity, which helps reduce operating costs. The synthesis of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) consists of three main chemical processes: (1) oxidation of \(\mathrm{S}\) to \(\mathrm{SO}_{2},(2)\) oxidation of \(\mathrm{SO}_{2}\) to \(\mathrm{SO}_{3},(3)\) the dissolving of \(\mathrm{SO}_{3}\) in \(\mathrm{H}_{2} \mathrm{SO}_{4}\) and its reaction with water to form \(\mathrm{H}_{2} \mathrm{SO}_{4}\). If the third process produces \(130 \mathrm{~kJ} / \mathrm{mol}\), how much heat is produced in preparing a mole of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) from a mole of \(\mathrm{S}\) ? How much heat is produced in preparing 5000 pounds of \(\mathrm{H}_{2} \mathrm{SO}_{4} ?\)

(a) What is the oxidation state of \(\mathrm{P}\) in \(\mathrm{PO}_{4}^{3-}\) and of \(\mathrm{N}\) in \(\mathrm{NO}_{3}^{-} ?(\mathbf{b})\) Why doesn't \(\mathrm{N}\) form a stable \(\mathrm{NO}_{4}^{3-}\) ion analogous to \(\mathrm{P} ?\)

Ultrapure germanium, like silicon, is used in semiconductors. Germanium of "ordinary" purity is prepared by the hightemperature reduction of \(\mathrm{GeO}_{2}\) with carbon. The Ge is converted to \(\mathrm{GeCl}_{4}\) by treatment with \(\mathrm{Cl}_{2}\) and then purified by distillation; \(\mathrm{GeCl}_{4}\) is then hydrolyzed in water to \(\mathrm{GeO}_{2}\) and reduced to the elemental form with \(\mathrm{H}_{2}\). The element is then zone refined. Write a balanced chemical equation for each of the chemical transformations in the course of forming ultrapure Ge from \(\mathrm{GeO}_{2}\)

The solubility of \(\mathrm{Cl}_{2}\) in \(100 \mathrm{~g}\) of water at \(\mathrm{STP}\) is \(310 \mathrm{~cm}^{3}\). Assume that this quantity of \(\mathrm{Cl}_{2}\) is dissolved and equilibrated as follows: $$ \mathrm{Cl}_{2}(a q)+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{Cl}^{-}(a q)+\mathrm{HClO}(a q)+\mathrm{H}^{+}(a q) $$ (a) If the equilibrium constant for this reaction is \(4.7 \times 10^{-4}\), calculate the equilibrium concentration of \(\mathrm{HClO}\) formed. \((\mathbf{b})\) What is the \(\mathrm{pH}\) of the final solution?

When ammonium perchlorate decomposes thermally, the products of the reaction are \(\mathrm{N}_{2}(g), \mathrm{O}_{2}(g), \mathrm{H}_{2} \mathrm{O}(g),\) and \(\mathrm{HCl}(g)\) (a) Write a balanced equation for the reaction. [Hint: You might find it easier to use fractional coefficients for the products.] (b) Calculate the enthalpy change in the reaction per mole of \(\mathrm{NH}_{4} \mathrm{ClO}_{4}\). The standard enthalpy of formation of \(\mathrm{NH}_{4} \mathrm{ClO}_{4}(s)\) is \(-295.8 \mathrm{~kJ}\) (c) When \(\mathrm{NH}_{4} \mathrm{ClO}_{4}(s)\) is employed in solid-fuel booster rockets, it is packed with powdered aluminum. Given the high temperature needed for \(\mathrm{NH}_{4} \mathrm{ClO}_{4}(s)\) decomposition and what the products of the reaction are, what role does the aluminum play? (d) Calculate the volume of all the gases that would be produced at STP, assuming complete reaction of one pound of ammonium perchlorate.

The dissolved oxygen present in any highly pressurized, hightemperature steam boiler can be extremely corrosive to its metal parts. Hydrazine, which is completely miscible with water, can be added to remove oxygen by reacting with it to form nitrogen and water. (a) Write the balanced equation for the reaction between gaseous hydrazine and oxygen. (b) Calculate the enthalpy change accompanying this reaction. (c) Oxygen in air dissolves in water to the extent of \(9.1 \mathrm{ppm}\) at \(20^{\circ} \mathrm{C}\) at sea level. How many grams of hydrazine are required to react with all the oxygen in \(3.0 \times 10^{4} \mathrm{~L}\) (the volume of a small swimming pool) under these conditions?

One method proposed for removing \(\mathrm{SO}_{2}\) from the flue gases of power plants involves reaction with aqueous \(\mathrm{H}_{2} \mathrm{~S}\). Elemental sulfur is the product. (a) Write a balanced chemical equation for the reaction. (b) What volume of \(\mathrm{H}_{2} \mathrm{~S}\) at \(27^{\circ} \mathrm{C}\) and 760 torr would be required to remove the \(\mathrm{SO}_{2}\) formed by burning 2.0 tons of coal containing \(3.5 \% \mathrm{~S}\) by mass? (c) What mass of elemental sulfur is produced? Assume that all reactions are \(100 \%\) efficient.

Manganese silicide has the empirical formula MnSi and melts at \(1280^{\circ} \mathrm{C}\). It is insoluble in water but does dissolve in aqueous HF. (a) What type of compound do you expect MnSi to be: metallic, molecular, covalent-network, or ionic? (b) Write a likely balanced chemical equation for the reaction of \(\mathrm{MnSi}\) with concentrated aqueous \(\mathrm{HF}\).

Chemists tried for a long time to make molecular compounds containing silicon- silicon double bonds; they finally succeed in \(1981 .\) The trick is having large, bulky R groups on the silicon atoms to make \(\mathrm{R}_{2} \mathrm{Si}=\mathrm{SiR}_{2}\) compounds. What experiments could you do to prove that a new compound has a silicon-silicon double bond rather than a silicon-silicon single bond?

Both dimethylhydrazine, \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NNH}_{2}\), and methylhydrazine, \(\mathrm{CH}_{3} \mathrm{NHNH}_{2}\), have been used as rocket fuels. When dinitrogen tetroxide \(\left(\mathrm{N}_{2} \mathrm{O}_{4}\right)\) is used as the oxidizer, the products are \(\mathrm{H}_{2} \mathrm{O}\) \(\mathrm{CO}_{2}\), and \(\mathrm{N}_{2}\). If the thrust of the rocket depends on the volume of the products produced, which of the substituted hydrazines produces a greater thrust per gram total mass of oxidizer plus fuel? [Assume that both fuels generate the same temperature and that \(\mathrm{H}_{2} \mathrm{O}(g)\) is formed. \(]\)

Borazine, \((\mathrm{BH})_{3}(\mathrm{NH})_{3},\) is an analog of \(\mathrm{C}_{6} \mathrm{H}_{6},\) benzene. It can be prepared from the reaction of diborane with ammonia, with hydrogen as another product; or from lithium borohydride and ammonium chloride, with lithium chloride and hydrogen as the other products. (a) Write balanced chemical equations for the production of borazine using both synthetic methods. (b) Draw the Lewis dot structure of borazine. (c) How many grams of borazine can be prepared from \(2.00 \mathrm{~L}\) of ammonia at STP, assuming diborane is in excess?