Boron hydrides were once evaluated for possible use as

Although the earth was formed from the same interstellar material as the sun, there is little elemental hydrogen (H2) in the earths atmosphere. Explain

List two major industrial uses of hydrogen

How do the acidities of the aqueous solutions of the alkaline earth metal ions (M2) 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 B and Si. Rationalize why these diagonal relationships hold for properties such as size, ionization energy, and electron affinity

Atomic size seems to play an important role in explaining some of the differences between the first element in a group and the subsequent group elements. Explain.

Silicon carbide (SiC) is an extremely hard substance. Propose a structure for SiC.

In most compounds, the solid phase is denser than the liquid phase. Why isnt this true for water?

What is nitrogen fixation? Give some examples of nitrogen fixation

All the Group 1A and 2A metals are produced by electrolysis of molten salts. Why?

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

Hydrogen is produced commercially by the reaction of methane with steam: a. Calculate H and S for this reaction (use the data in Appendix 4) b. What temperatures will favor product formation at standard conditions? Assume H and S do not depend on temperature

The major industrial use of hydrogen is in the production of ammonia by the Haber process: a. Using data from Appendix 4, calculate H, S, and G for the Haber process reaction. b. Is the reaction spontaneous at standard conditions? c. At what temperatures is the reaction spontaneous at standard conditions? Assume H and S do not depend on temperature

Write balanced equations describing the reaction of lithium metal with each of the following: O2, S, Cl2, P4, H2, H2O, 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).

What are the three types of hydrides? How do they differ?

Reference Table 20.5 and give examples of the three types of alkali metal oxides that form. How do they differ?

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 20.4?

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: O2, S, Cl2, P4, H2, H2O, and HCl.

The U.S. Public Health Service recommends the fluoridation of water as a means for preventing tooth decay. The recommended concentration is 1 mg F per liter. The presence of calcium ions in hard water can precipitate the added fluoride. What is the maximum molarity of calcium ions in hard water if the fluoride concentration is at the USPHS recommended level? (Ksp for CaF2  4.0  1011.)

Slaked lime, Ca(OH)2, is used to soften hard water by removing calcium ions from hard water through the reaction Although CaCO3(s) is considered insoluble, some of it does dissolve in aqueous solutions. Calculate the molar solubility of CaCO3 in water (Ksp  8.7  109 ).

What mass of barium is produced when molten BaCl2 is electrolyzed by a current of 2.50  105 A for 6.00 h?

Electrolysis of an alkaline earth metal chloride using a current of 5.00 A for 748 s deposits 0.471 g of metal at the cathode. What is the identity of the alkaline earth metal chloride?

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

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

Assume that element 113 has been produced. 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

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: F2, O2, S, and HCl.

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

Al2O3 is amphoteric. What does this mean?

What are three-centered bonds?

Discuss the importance of the and bond strengths and of bonding to the properties of carbon and silicon.

Besides the central atom, what are the differences between CO2 and SiO2?

The three most stable oxides of carbon are carbon monoxide (CO), carbon dioxide (CO2), and carbon suboxide (C3O2). The space-filling models for these three compounds are For each oxide, draw the Lewis structure, predict the molecular structure, and describe the bonding (in terms of the hybrid orbitals for the carbon atoms)

Carbon and sulfur form compounds with the formulas CS2 and C3S2. Draw Lewis structures and predict the shapes of these two compounds.

Silicon is produced for the chemical and electronics industries by the following reactions. Give the balanced equation for each reaction. a. b. Silicon tetrachloride is reacted with very pure magnesium, producing silicon and magnesium chloride.

Write equations describing the reactions of Sn with each of the following: Cl2, O2, and HCl.

The compound Pb3O4 (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 Pb3O4?

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 (NO3 ). The corresponding oxyanion of phosphorus is PO4 3. The NO4 3 ion is known but not very stable. The PO3 ion is not known. Account for these differences in terms of the bonding in the four anions. 4

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. NF5 or PF5 b. AsF5 or AsI5 c. NF3 or NBr3

Write balanced equations for the reactions described in Table 20.13 for the production of Bi and Sb.

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 5A elements can form molecules or ions that involve three, five, or six covalent bonds; NH3, AsCl5, and PF6 are examples. Draw the Lewis structure for each of these substances, and predict the molecular structure and hybridization for each. Why doesnt NF5 or NCl6 form?

Lewis structures can be used to understand why some molecules react in certain ways. Write the Lewis structure for the reactants and products in the reactions described below. a. Nitrogen dioxide dimerizes to produce dinitrogen tetroxide. b. Boron trihydride accepts a pair of electrons from ammonia, forming BH3NH3. Give a possible explanation for why these two reactions occur.

Hydrazine (N2H4) is used as a fuel in liquid-fueled rockets. When hydrazine reacts with oxygen gas, nitrogen gas and water vapor are produced. Write a balanced equation and use bond energies from Table 8.4 to estimate H for this reaction

The space shuttle orbiter utilizes the oxidation of methylhydrazine by dinitrogen tetroxide for propulsion: Calculate H for this reaction using data in Appendix 4

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.

Using data from Appendix 4 calculate H, S, and G for the reaction Why does NO form in an automobile engine but then does not readily decompose back to N2 and O2 in the atmosphere?

Compare the Lewis structures with the molecular orbital view of the bonding in NO, NO, and NO. Account for any discrepancies between the two models.

The N2O molecule is linear and polar. a. On the basis of this experimental evidence, which arrangement, NNO or NON, is correct? Explain your answer. b. On the basis of your answer to part a, write the Lewis structure of N2O (including resonance forms). Give the formal charge on each atom and the hybridization of the central atom. c. How would the multiple bonding in be described in terms of orbitals?

Phosphoric acid (H3PO4) is a triprotic acid, phosphorous acid (H3PO3) is a diprotic acid, and hypophosphorous acid (H3PO2) is a monoprotic acid. Explain this phenomenon

Trisodium phosphate (TSP) is an effective grease remover. Like many cleaners, TSP acts as a base in water. Write a balanced equation to account for this basic behavior

Use bond energies to estimate the maximum wavelength of light that will cause the reaction

The xerographic (dry writing) process was invented in 1938 by C. Carlson. In xerography, an image is produced on a photoconductor by exposing it to light. Selenium is commonly used, since its conductivity increases three orders of magnitude upon exposure to light in the range from 400 to 500 nm. What color light should be used to cause selenium to become conductive? (See Figure 7.2.)

Write a balanced equation describing the reduction of H2SeO4 by SO2 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 sucrose (C12H22O11)

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?

Ozone is a possible replacement for chlorine in municipal water purification. Unlike chlorine, virtually no ozone remains after treatment. This has good and bad consequences. Explain.

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. 6

An unknown element is a nonmetal and has a valence electron configuration of ns2 np4 . a. How many valence electrons does this element have? b. What are some possible identities for this element? c. What is the formula of the compound(s) this element would form with lithium? hydrogen? magnesium? aluminum? fluorine?

How can the paramagnetism of O2 be explained using the molecular orbital model?

Describe the bonding in SO2 and SO3 using the localized electron model (hybrid orbital theory). How would the molecular orbital model describe the bonding in these two compounds?

Write the Lewis structure for O2F2. Predict the bond angles and hybridization of the two central oxygen atoms. Assign oxidation states and formal charges to the atoms in O2F2. The compound O2F2 is a vigorous and potent oxidizing and fluorinating agent. Are oxidation states or formal charges more useful in accounting for these properties of O2F2?

Give the Lewis structure, molecular structure, and hybridization of the oxygen atom for OF2. Would you expect OF2 to be a strong oxidizing agent like O2F2 discussed in Exercise 67?

Fluorine reacts with sulfur to form several different covalent compounds. Three of these compounds are SF2, SF4, and SF6. Draw the Lewis structures for these compounds, and predict the molecular structures (including bond angles). Would you expect OF4 to be a stable compound?

Predict some possible compounds that could form between chlorine and selenium. (Hint: See the preceding exercise.)

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

Explain why HF is a weak acid, whereas HCl, HBr, and HI are all strong acids

Hydrazine is somewhat toxic. Use the following half-reactions to explain why household bleach (highly alkaline solution of sodium hypochlorite) should not be mixed with household ammonia or glass cleansers that contain ammonia

What is a disproportionation reaction? Use the following reduction potentials to predict whether HClO2 will disproportionate

The xenon halides and oxides are isoelectronic with many other compounds and ions containing halogens. Give a molecule or ion in which iodine is the central atom that is isoelectronic with each of the following. a. xenon tetroxide d. xenon tetrafluoride b. xenon trioxide e. xenon hexafluoride c. xenon difluoride

For each of the following, write the Lewis structure(s), predict the molecular structure (including bond angles), and give the expected hybridization of the central atom. a. KrF2 b. KrF4 c. XeO2F2 d. XeO2F4

Although He is the second most abundant element in the universe, it is very rare on earth. Why?

The noble gas with the largest atmospheric abundance is argon. Using the data in Table 20.22, calculate the mass of argon at 25C and 1.0 atm in a room 10.0 m  10.0 m  10.0 m. How many Ar atoms are in this room? How many Ar atoms do you inhale in one breath (approximately 2 L) of air at 25C and 1.0 atm? Argon gas is inert, so it poses no serious health risks. However, if significant amounts of radon are inhaled into the lungs, lung cancer is a possible result. Explain the health risk differences between argon gas and radon gas.

There is evidence that radon reacts with fluorine to form compounds similar to those formed by xenon and fluorine. Predict the formulas of these RnFx compounds. Why is the chemistry of radon difficult to study?

For the RnFx compounds you predicted in the preceding exercise, give the molecular structure (including bond angles).

Which do you think would be the greater health hazard, the release of a radioactive nuclide of Sr or a radioactive nuclide of Xe into the environment? Assume the amount of radioactivity is the same in each case. Explain your answer on the basis of the chemical properties of Sr and Xe. Why are the chemical properties of a radioactive substance important in assessing its potential health hazards?

The most significant source of natural radiation is radon-222. 222Rn, a decay product of 238U, is continuously generated in the earths crust, allowing gaseous Rn to seep into the basements of buildings. Because 222Rn is an -particle producer with a relatively short half-life of 3.82 days, it can cause biological damage when inhaled. a. How many particles and  particles are produced when 238U decays to 222Rn? What nucleus is produced when 222Rn decays? b. Radon is a noble gas so one would expect it to pass through the body quickly. Why is there a concern over inhaling 222Rn?

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.

Provide a reasonable estimate for the number of atoms in a 150-lb adult human. Explain your answer. Use the information given in Table 20.2

In the 1950s and 1960s, 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?

EDTA is used as a complexing agent in chemical analysis. Solutions of EDTA, usually containing the disodium salt Na2H2EDTA, are also used to treat heavy metal poisoning. The equilibrium constant for the following reaction is 1.0  1023: Calculate [Pb2] at equilibrium in a solution originally 0.0010 M in Pb2, 0.050 M in H2EDTA2, and buffered at pH  6.00.

Bacterial digestion is an economical method of sewage treatment. The reaction Bacterial tissue is an intermediate step in the conversion of the nitrogen in organic compounds into nitrate ions. How much bacterial tissue is produced in a treatment plant for every 1.0  104 kg of wastewater containing 3.0% NH4 ions by mass? Assume that 95% of the ammonium ions are consumed by the bacteria.

Phosphate buffers are important in regulating the pH of intracellular fluids at pH values generally between 7.1 and 7.2. What is the concentration ratio of H2PO4 to HPO4 2 in intracellular fluid at pH  7.15? Why is a buffer composed of H3PO4 and H2PO4 ineffective in buffering the pH of intracellular fluid? H3PO41aq2 H2PO4 1aq2 H1aq2 Ka  7.5  103 104

Hydrogen peroxide is used as a cleaning agent in the treatment of cuts and abrasions for several reasons. It is an oxidizing agent that can directly kill many microorganisms; it decomposes upon contact with blood, releasing elemental oxygen gas (which inhibits the growth of anaerobic microorganisms); and it foams upon contact with blood, which provides a cleansing action. In the laboratory, small quantities of hydrogen peroxide can be prepared by the action of an acid on an alkaline earth metal peroxide, such as barium peroxide: What mass of hydrogen peroxide can result when 1.50 g barium peroxide is treated with 25.0 mL hydrochloric acid solution containing 0.0272 g HCl per mL? What mass of which reagent is left unreacted?

In large doses, selenium is toxic. However, in moderate intake, selenium is a physiologically important element. How is selenium physiologically important?

It takes 15 kWh (kilowatt-hours) of electrical energy to produce 1.0 kg of aluminum metal from aluminum oxide by the HallHeroult process. Compare this to the amount of energy necessary to melt 1.0 kg of aluminum metal. Why is it economically feasible to recycle aluminum cans? (The enthalpy of fusion for aluminum metal is 10.7 kJ/mol [1 watt  1 J/s].)

The inert-pair effect is sometimes used to explain the tendency of heavier members of Group 3A to exhibit 1 and 3 oxidation states. What does the inert-pair effect reference? (Hint: Consider the valence electron configuration for Group 3A elements.)

Calculate the pH of a 0.050 M Al(NO3)3 solution. The Ka value for Al(H2O)6 3 is 1.4  105 .

The compound with the formula TlI3 is a black solid. Given the following standard reduction potentials: would you formulate this compound as thallium(III) iodide or thallium(I) triiodide?

How could you determine experimentally whether the compound Ga2Cl4 contains two gallium(II) ions or one gallium(I) and one gallium(III) ion? (Hint: Consider the electron configurations of the three possible ions.)

The resistivity (a measure of electrical resistance) of graphite is (0.4 to 5.0)  104 ohm cm in the basal plane. (The basal plane is the plane of the six-membered rings of carbon atoms.) The resistivity is 0.2 to 1.0 ohm cm along the axis perpendicular to the plane. The resistivity of diamond is 1014 to 1016 ohm cm and is independent of direction. How can you account for this behavior in terms of the structures of graphite and diamond? 97

The compound NF3 is quite stable, but NCl3 is very unstable (NCl3 was first synthesized in 1811 by P. L. Dulong, who lost three fingers and an eye studying its properties). The compounds NBr3 and NI3 are rare, although the explosive compound NI3 NH3 is known. Account for the instability of these halides of nitrogen.

Photogray lenses contain small embedded crystals of solid silver chloride. Silver chloride is light-sensitive because of the reaction Small particles of metallic silver cause the lenses to darken. In the lenses this process is reversible. When the light is removed, the reverse reaction occurs. However, when pure white silver chloride is exposed to sunlight it darkens; the reverse reaction does not occur in the dark. a. How do you explain this difference? b. Photogray lenses do become permanently dark in time. How do you account for this?

Ammonia is produced by the Haber process, in which nitrogen and hydrogen are reacted directly using an iron mesh impregnated with oxides as a catalyst. For the reaction equilibrium constants (Kp values) as a function of temperature are

The synthesis of ammonia gas from nitrogen gas and hydrogen gas represents a classic case in which a knowledge of kinetics and equilibrium was used to make a desired chemical reaction economically feasible. Explain how each of the following conditions helps to maximize the yield of ammonia. a. running the reaction at an elevated temperature b. removing the ammonia from the reaction mixture as it forms c. using a catalyst d. running the reaction at high pressure

Nitric acid is produced commercially by the Ostwald process, represented by the following equations: What mass of NH3 must be used to produce 1.0  106 kg HNO3 by the Ostwald process? Assume 100% yield in each reaction and assume that the NO produced in the third step is not recycled.

Draw Lewis structures for the AsCl4 and AsCl6 ions. What type of reaction (acidbase, oxidationreduction, or the like) is the following?

The unit cell for a pure xenon fluoride compound is shown below. What is the formula of the compound? Xenon Fluorine

Halogens form a variety of covalent compounds with each other. For example, chlorine and fluorine form the compounds ClF, ClF3, and ClF5. Predict the molecular structure (including bond angles) for each of these three compounds. Would you expect FCl3 to be a stable compound? Explain.

Suppose 10.00 g of an alkaline earth metal reacts with 10.0 L water to produce 6.10 L hydrogen gas at 1.00 atm and 25C. Identify the metal and determine the pH of the solution.

a. Many biochemical reactions that occur in cells require relatively high concentrations of potassium ion (K). The concentration of K in muscle cells is about 0.15 M. The concentration of K in blood plasma is about 0.0050 M. The high internal concentration in cells is maintained by pumping K from the plasma. How much work must be done to transport 1.0 mol K from the blood to the inside of a muscle cell at 37C (normal body temperature)? b.

b. When 1.0 mol K is transferred from blood to the cells, do any other ions have to be transported? Why or why not?

c. Cells use the hydrolysis of adenosine triphosphate, abbreviated ATP, as a source of energy. Symbolically, this reaction can be represented as where ADP represents adenosine diphosphate. For this reaction at 37C, K  1.7  105 . How many moles of ATP must be hydrolyzed to provide the energy for the transport of 1.0 mol K? Assume standard conditions for the ATP hydrolysis reaction.

One reason suggested to account for the instability of long chains of silicon atoms is that the decomposition involves the transition state shown below: The activation energy for such a process is 210 kJ/mol, which is less than either the or energy. Why would a similar mechanism not be expected to be very important in the decomposition of long carbon chains?

From the information on the temperature stability of white and gray tin given in this chapter, which form would you expect to have the more ordered structure (have the smaller positional probability)?

Lead forms compounds in the 2 and 4 oxidation states. All lead(II) halides are known (and are known to be ionic). Only PbF4 and PbCl4 are known among the possible lead(IV) halides. Presumably lead(IV) oxidizes bromide and iodide ions, producing the lead(II) halide and the free halogen: PbX4 PbX2 X2 S Suppose 25.00 g of a lead(IV) halide reacts to form 16.12 g of a lead(II) halide and the free halogen. Identify the halogen

Many structures of phosphorus-containing compounds are drawn with some bonds. These bonds are not the typical bonds weve considered, which involve the overlap of two p orbitals. Instead, they result from the overlap of a d orbital on the phosphorus atom with a p orbital on oxygen. This type of bonding is sometimes used as an explanation for why H3PO3 has the first structure below rather than the second: Draw a picture showing how a d orbital and a p orbital overlap to form a bond. 1

Use bond energies (Table 8.4) to show that the preferred products for the decomposition of N2O3 are NO2 and NO rather than O2 and N2O. (The single bond energy is 201 kJ/mol.) Hint: Consider the reaction kinetics

Sodium tripolyphosphate (Na5P3O10) is used in many synthetic detergents to soften the water by complexing Mg2 and Ca2 ions. It also increases the efficiency of surfactants (wetting agents) that lower a liquids surface tension. The K value for the formation of MgP3O103 is 4.0  108 . The reaction is Calculate the concentration of Mg2 in a solution that was originally 50. ppm of Mg2 (50. mg/L of solution) after 40. g Na5P3O10 is added to 1.0 L of the solution. 11

One pathway for the destruction of ozone in the upper atmosphere is Slow Fast a. Which species is a catalyst? b. Which species is an intermediate? c. The activation energy Ea for the uncatalyzed reaction is 14.0 kJ. Ea for the same reaction when catalyzed by the presence of NO is 11.9 kJ. What is the ratio of the rate constant for the catalyzed reaction to that for the uncatalyzed reaction at 25C? Assume that the frequency factor A is the same for each reaction. d. One of the concerns about the use of Freons is that they will migrate to the upper atmosphere, where chlorine atoms can be generated by the reaction Freon-12 Chlorine atoms also can act as a catalyst for the destruction of ozone. The first step of a proposed mechanism for chlorinecatalyzed ozone destruction is Cl1g2 O31g2 ClO1g2 O21g2 Slow Assuming a two-step mechanism, propose the second step in the mechanism and give the overall balanced equation. e. The activation energy for Cl-catalyzed destruction of ozone is 2.1 kJ/mol. Estimate the efficiency with which Cl atoms destroy ozone as compared with NO molecules at 25C. Assume that the frequency factor A is the same for each catalyzed reaction and assume similar rate laws for each catalyzed reaction.

Using data from Appendix 4, calculate H, G, and Kp (at 298 K) for the production of ozone from oxygen: At 30 km above the surface of the earth, the temperature is about 230. K, and the partial pressure of oxygen is about 1.0  103 atm. Estimate the partial pressure of ozone in equilibrium with oxygen at 30 km above the earths surface. Is it reasonable to assume that the equilibrium between oxygen and ozone is maintained under these conditions? Explain.

You travel to a distant, cold planet where the ammonia flows like water. In fact, the inhabitants of this planet use ammonia (an abundant liquid on their planet) much as earthlings use water. Ammonia is also similar to water in that it is amphoteric and undergoes autoionization. The K value for the autoionization of ammonia is 1.8  1012 at the standard temperature of the planet. What is the pH of ammonia at this temperature?

Nitrogen gas reacts with hydrogen gas to form ammonia gas. You have an equimolar mixture of nitrogen and hydrogen gases in a 15.0-L container fitted with a piston in a room with a pressure of 1.00 atm. The piston apparatus allows the container volume to change in order to keep the pressure constant at 1.00 atm. Assume ideal behavior, constant temperature, and complete reaction. a. What is the partial pressure of ammonia in the container when the reaction is complete? b. What is the mole fraction of ammonia in the container when the reaction is complete? c. What is the volume of the container when the reaction is complete?

A cylinder fitted with a movable piston initially contains 2.00 mol O2(g) and an unknown amount of SO2(g). The oxygen is known to be in excess. The density of the mixture is 0.8000 g/L at some T and P. After the reaction has gone to completion, forming SO3(g), the density of the resulting gaseous mixture is 0.8471 g/L at the same T and P. Calculate the mass of SO3 formed in the reaction.

The heaviest member of the alkaline earth metals is radium (Ra), a naturally radioactive element discovered by Pierre and Marie Curie in 1898. Radium was initially isolated from the uranium ore pitchblende, in which it is present as approximately 1.0 g per 7.0 metric tons of pitchblende. How many atoms of radium can be isolated from 1.75  108 g pitchblende (1 metric ton 1000 kg)? One of the early uses of radium was as an additive to paint so that watch dials coated with this paint would glow in the dark. The longest-lived isotope of radium has a half-life of 1.60  103 years. If an antique watch, manufactured in 1925, contains 15.0 mg radium, how many atoms of radium will remain in 2025?

Indium(III) phosphide is a semiconducting material that has been frequently used in lasers, light-emitting diodes (LED), and fiberoptic devices. This material can be synthesized at 900. K according to the following reaction: a. If 2.56 L In(CH3)3 at 2.00 atm is allowed to react with 1.38 L PH3 at 3.00 atm, what mass of InP(s) will be produced assuming the reaction is 87% efficient? b. When an electric current is passed through an optoelectronic device containing InP, the light emitted has an energy of 2.03  1019 J. What is the wavelength of this light and is it visible to the human eye? c. The semiconducting properties of InP can be altered by doping. If a small number of phosphorus atoms are replaced by atoms with an electron configuration of [Kr]5s 2 4d105p4 , is this n-type or p-type doping?

Although nitrogen trifluoride (NF3) is a thermally stable compound, nitrogen triiodide (NI3) is known to be a highly explosive material. NI3 can be synthesized according to the equation a. What is the enthalpy of formation for NI3(s) given the enthalpy of reaction (307 kJ) and the enthalpies of formation for BN(s) (254 kJ/mol), IF(g) (96 kJ/mol), and BF3(g) (1136 kJ/mol)? b. It is reported that when the synthesis of NI3 is conducted using 4 mol IF for every 1 mol BN, one of the by-products isolated is [IF2] [BF4] . What are the molecular geometries of the species in this by-product? What are the hybridizations of the central atoms in each species in the by-product? 121.

While selenic acid has the formula H2SeO4 and thus is directly related to sulfuric acid, telluric acid is best visualized as H6TeO6 or Te(OH)6. a. What is the oxidation state of tellurium in Te(OH)6? b. Despite its structural differences with sulfuric and selenic acid, telluric acid is a diprotic acid with pKa1  7.68 and pKa2  11.29. Telluric acid can be prepared by hydrolysis of tellurium hexafluoride according to the equation Tellurium hexafluoride can be prepared by the reaction of elemental tellurium with fluorine gas: If a cubic block of tellurium (density  6.240 g/cm3 ) measuring 0.545 cm on edge is allowed to react with 2.34 L fluorine gas at 1.06 atm and 25C, what is the pH of a solution of Te(OH)6 formed by dissolving the isolated TeF6(g) in 115 mL water?

Captain Kirk has set a trap for the Klingons who are threatening an innocent planet. He has sent small groups of fighter rockets to sites that are invisible to Klingon radar and put a decoy in the open. He calls this the fishhook strategy. Mr. Spock has sent a coded message to the chemists on the fighters to tell the ships what to do next. The outline of the message is (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (10) (11) Fill in the blanks of the message using the following clues. (1) Symbol of the halogen whose hydride has the second highest boiling point in the series of HX compounds that are hydrogen halides. (2) Symbol of the halogen that is the only hydrogen halide, HX, that is a weak acid in aqueous solution. (3) Symbol of the element whose existence on the sun was known before its existence on earth was discovered. (4) The Group 5A element in Table 20.13 that should have the most metallic character. (5) Symbol of the Group 6A element that, like selenium, is a semiconductor. (6) Symbol for the element known in rhombic and monoclinic forms. (7) Symbol for the element that exists as diatomic molecules in a yellow-green gas when not combined with another element. (8) Symbol for the most abundant element in and near the earths crust. (9) Symbol for the element that seems to give some protection against cancer when a diet rich in this element is consumed. (10) Symbol for the smallest noble gas that forms compounds with fluorine having the general formula AF2 and AF4 (reverse the symbol and split the letters as shown). (11) Symbol for the toxic element that, like phosphorus and antimony, forms tetrameric molecules when uncombined with other elements (split the letters of the symbol as shown). (12) Symbol for the element that occurs as an inert component of air but is a very prominent part of fertilizers and explosives

Use the symbols of the elements described in the following clues to fill in the blanks that spell out the name of a famous American scientist. Although this scientist was better known as a physicist than as a chemist, the Philadelphia institute that bears his name does include a biochemistry research facility. (1) (2) (3) (4) (5) (6) (7) (1) The oxide of this alkaline earth metal is amphoteric. (2) The element that makes up approximately 3.0% by mass of the human body. (3) The element having a 7s 1 valence electron configuration. (4) This element is the alkali metal with the least negative standard reduction potential. Write its symbol in reverse order. (5) The alkali metal whose ion is more concentrated in intracellular fluids as compared with blood plasma. (6) This is the only alkali metal that reacts directly with nitrogen to make a binary compound with formula M3N. (7) This element is the first in Group 3A for which the 1 oxidation state is exhibited in stable compounds. Use only the second letter of its symbol.