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The Chemistry of the Nonmetals
4. Which of the following elements can exist as a triatomic molecule?
(a) hydrogen (b) helium (c) sulfur (d) oxygen (e) chlorine
5. Which of the following elements should form compounds with the formulas Na2X, H2X, XO2, and XF6?
(a) B (b) C (c) N (d) O (e) S
6. Which of the following elements should form compounds with the formulas XH3, XF3, and Na3XO4?
(a) Al (b) Ge (c) As (d) S (e) Cl
7. Which of the following can’t be found in nature? Explain why.
(a) MgCl2 (b) CaCO3 (c) F2 (d) Na3AlF6 (e) NaCl
The Role of Nonmetal Elements in Chemical Reactions
8. Explain why more electronegative elements tend to oxidize less electronegative elements.
9. Which of the following ions or molecules can be oxidized?
(a) H2SO3 (b) P4 (c) Cl (d) SiO2 (e) PO43 (f) Mg2 10. Which of the following ions or molecules can be reduced?
(a) H2O (b) H2SO3 (c) HCl (d) CO2 (e) Mg2 (f) Na
Deciding What Is Oxidized and What Is Reduced
11. For each of the following reactions, identify what is oxidized and what is reduced.
(a) Fe2O3(s) 3 CO(g) n 2 Fe(s) 3 CO2(g) (b) H2(g) CO2(g) n H2O(g) CO(g) (c) CH4(g) 2 O2(g) n CO2(g) 2 H2O(g) (d) 2 H2S(g) 3 O2(g) n 2 SO2(g) 2 H2O(g)
12. For each of the following reactions, identify what is oxidized and what is reduced.
(a) PH3(g) 3 Cl2(g) n PCl3(g) 3 HCl(g) (b) 2 NO(g) F2(g) n 2 NOF(g)
(c) 2 Na(s) 2 NH3(l) n 2 NaNH2(s) H2(g) (d) 3 NO2(g) H2O(l) n 2 HNO3(aq) NO(g)
13. Hydrazine is made by a reaction known as the Raschig process.
2 NH3(aq) NaOCl(aq) 88n N2H4(aq) NaCl(aq) H2O(l )
Decide whether this is an oxidation–reduction reaction. If it is, identify the compound oxidized and the compound reduced.
14. The thiosulfate ion, S2O32, is prepared by boiling solutions of sulfur dissolved in sodium sulfite.
8 SO32(aq) S8(s) 88n 8 S2O32(aq)
Is this an oxidation–reduction reaction? If it is, identify the compound oxidized and the compound reduced.
15. Chlorine dioxide, ClO2, is used commercially as a bleach or a disinfectant because of its excellent oxidizing ability. ClO2is prepared by decomposing chlorous acid as follows.
8 HOClO(aq) 88n 6 ClO2(g) Cl2(g) 4 H2O(l )
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Is this an oxidation–reduction reaction? If it is, identify the oxidizing agent and the re-ducing agent.
16. Nitric acid sometimes acts as an acid (as a source of the H ion) and sometimes as an oxidizing agent. For each of the following reactions, decide whether HNO3acts as an acid or as an oxidizing agent.
(a) Na2CO3(s) 2 HNO3(aq) n 2 NaNO3(aq) CO2(g) H2O(l) (b) 3 P4(s) 20 HNO3(aq) 8 H2O(l) n 12 H3PO4(aq) 20 NO(g) (c) Al2O3(s) 6 HNO3(aq) n 2 Al(NO3)3(aq) 3 H2O(l)
(d) 3 Cu(s) 8 HNO3(aq) n 3 Cu(NO3)2(aq) 2 NO(g) 4 H2O(l) 17. Which of the following would you expect to be the best oxidizing agent?
(a) Na (b) H2 (c) N2 (d) P4 (e) O2
18. Which of the following would you expect to be the best reducing agent?
(a) Na (b) F (c) Na (d) Br2 (e) Fe3
19. For each of the following pairs of elements, determine which is the better reducing agent?
(a) P4or As (b) As or S8 (c) P4or S8 (d) S8or Cl2 (e) C or O2
Predicting the Products of Chemical Reactions 20. Predict the products of the following reactions.
(a) Mg(s) N2(g) n (b) Li(s) O2(g) n (c) Br2(l) I(aq) n
21. Predict the products of the following reactions.
(a) SO2(g) H2O(l) n (b) Cl2(g) OH(aq) n (c) CO2(g) H2O(l) n
22. Predict the products of the following reactions.
(a) HCl(g) H2O(l) n (b) P4O10(s) H2O(l) n (c) NO2(g) H2O(l) n
23. Predict the products of the following reactions.
(a) S8(s) O2(g) n (b) Al(s) I2(s) n (c) P4(s) F2(g) n
The Chemistry of Hydrogen
24. Describe three ways of preparing small quantities of H2in the lab.
25. Explain why it is not a good idea to prepare H2by reacting sodium metal with a strong acid.
26. Give an example of a compound in which hydrogen has an oxidation number of 1;
of 0; of 1.
27. Which of the following reactions produce a compound in which hydrogen has an oxi-dation number of 1?
(a) Li H2n (b) O2 H2n (c) S8 H2n (d) Cl2 H2n (e) Ca H2n
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28. Use tables of first ionization energies and electronegativities to explain why it is so dif-ficult to decide whether hydrogen belongs in Group IA or Group VIIA of the peri-odic table.
29. Which of the following substances can be used as evidence for placing hydrogen in Group IA? Which can be used as evidence for including hydrogen in Group VIIA?
(a) CaH2 (b) AlH3 (c) H2S (d) H3PO4 (e) H2
30. The earth’s atmosphere once contained significant amounts of H2. Explain why only traces of H2 are left in the earth’s atmosphere, whereas the atmospheres of other planets—such as Jupiter, Saturn, and Neptune—contain large quantities of H2. 31. Use Lewis structures to explain what happens in the four reactions described in
Sec-tion N.2 that can be used to prepare small quantities of H2gas.
The Chemistry of Oxygen and Sulfur
32. Describe three ways of preparing small quantities of O2in the lab.
33. Describe the relationships among oxygen (O2), the peroxide ion (O22), and the oxide ion (O2). Explain why the number of electrons shared by a pair of oxygen atoms decreases as the oxidation number of the oxygen becomes more negative.
34. Which of the following elements or compounds could eventually produce O2 when it reacts with water?
(a) Ba (b) BaO (c) BaO2 (d) Ba(OH)2 (e) BaNO3
35. Explain why the only compounds in which oxygen has a positive oxidation number are compounds, such as OF2, that contain fluorine.
36. Explain why hydrogen peroxide can be either an oxidizing agent or a reducing agent.
Describe at least one reaction in which H2O2oxidizes another substance and one re-action in which it reduces another substance.
37. Write the Lewis structures for ozone, O3, and sulfur dioxide, SO2. Discuss the rela-tionship between the compounds.
38. Explain why elemental oxygen exists as O2molecules, whereas elemental sulfur forms S8molecules.
39. Explain why sulfur forms compounds such as SF4and SF6, when oxygen can only form OF2.
40. Describe the relationship between the thiosulfate and sulfate ions and between the thiocyanate and cyanate ions. Use that relationship to predict the formula of the trithio-carbonate ion.
41. Write the Lewis structures of the following products of the reaction between sodium and sulfur.
(a) Na2S (b) Na2S2 (c) Na2S3 (d) Na2S8
42. Explain why sulfur readily forms compounds in the 2, 4, and 6 oxidation states, but only a handful of compounds exist in which oxygen is in a positive oxidation state.
43. Explain why sulfur-containing compounds such as FeS2, CS2, and H2S form SO2 in-stead of SO3 when they burn.
44. Use Lewis structures to explain why solutions of the SO32 ion react with sulfur to form thiosulfate, S2O32.
45. Use Lewis structures to explain why a two-electron reduction of the S2O62ion gives SO32.
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46. Use Lewis structures to explain why a two-electron oxidation of the S2O32ion gives the S4O62 ion.
47. Which of the following does not have a reasonable oxidation number for sulfur?
(a) Na2S (b) H2S (c) SO32 (d) SO4 (e) SF4
48. Explain why SO2 plays an important role in the phenomenon known as acid rain.
49. Explain why problems with acid rain would be much more severe if sulfur compounds burned to form SO3instead of SO2.
The Chemistry of Nitrogen and Phosphorus
50. Nitrogen has a reasonable oxidation number in all of the following compounds, and yet one of them is still impossible. Which one is impossible?
(a) NF3 (b) NF5 (c) NO3 (d) NO2 (e) NO
51. Earth’s atmosphere contains roughly 4 1016tons of nitrogen, and yet the biggest prob-lem facing agriculture in the world today is a lack of “nitrogen.” Explain why.
52. Explain why elemental nitrogen is almost inert, but nitrogen compounds such as NH4NO3, NaN3, nitroglycerin, and trinitrotoluene (TNT) form some of the most dan-gerous explosives.
53. Which of the following oxides of nitrogen are paramagnetic?
(a) N2O (b) NO (c) NO2 (d) N2O3 (e) N2O4 (f) N2O5
54. Use Lewis structures to explain what happens in the following reaction.
2 NO O2 88n 2 NO2
55. Use Lewis structures to explain why NO reacts with NO2to form N2O3when a mix-ture of the compounds is cooled.
56. Use the fact that nitrous oxide decomposes to form nitrogen and oxygen to explain why a glowing splint bursts into flame when immersed in a container filled with N2O.
2 N2O(g) 88n 2 N2(g) O2(g)
57. Describe ways of preparing small quantities of each of the following compounds in the laboratory.
(a) N2O (b) NO (c) NO2 (d) N2O4
58. Describe how to tell the difference between a flask filled with NO gas and a flask filled with NO2.
59. Lightning catalyzes the reaction between nitrogen and oxygen in the atmosphere to form nitrogen oxide, NO.
N2(g) O2(g) 88n 2 NO(g) Explain how lightning acts as one source of acid rain.
60. Which of the following elements or compounds is not involved at some stage in the preparation of nitric acid?
(a) O2 (b) N2 (c) NO (d) NO2 (e) H2
61. Explain why phosphorus forms both PCl3and PCl5but nitrogen forms only NCl3. 62. Explain why nitrogen is essentially inert at room temperature, but white phosphorus
bursts spontaneously into flame when it comes into contact with air.
63. Explain why red phosphorus is much less reactive than white phosphorus.
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64. Explain why nitrogen forms extraordinarily stable N2molecules at room temperature, but phosphorus forms P2molecules only at very high temperatures.
65. Explain why nitric acid has the formula HNO3and phosphoric acid has the formula H3PO4. 66. Write the Lewis structures for phosphoric acid, H3PO4, and phosphorous acid, H3PO3. Explain why phosphoric acid can lose three H ions to form a phosphate ion, PO43, whereas phosphorous acid can lose only two H ions to form the HPO32ion.
67. Explain why only two of the four hydrogen atoms in H4P2O5 are lost when the oxy-acid forms an oxyanion.
68. Describe the role of carbon in the preparation of elemental phosphorus from calcium phosphate.
69. Predict the product of the reaction of phosphorus with excess oxygen and then predict what will happen when the product of the reaction is dissolved in water.
70. Explain why the most common oxidation states of antimony are 3 and 5.
71. Which of the following compounds should not exist?
(a) Na3P (b) (NH4)3PO4 (c) PO2 (d) PH3 (e) POCl3
The Chemistry of the Halogens
72. Which of the halogens is the most active, or reactive? Explain why.
73. Describe the difference between halogens and halides. Give examples of each.
74. Fe3 ions can oxidize Brions to Br2, but they can’t oxidize Clions to Cl2. Use this information to determine where the Fe3ion belongs in the following sequence of de-creasing oxidizing strength: F2 Cl2 Br2 I2.
75. HBr can be prepared by reacting PBr3with water.
PBr3(l) 3 H2O(l ) 88n 3 HBr(aq) H3PO3(aq) Use this information to explain what happens in the following reaction.
P4(s) 6 Br2(s) 12 H2O(l ) 88n 12 HBr(aq) 4 H3PO3(aq) 76. Explain why chlorine reacts with fluorine to form ClF3 but not FCl3. 77. Chlorine reacts with base to form the hypochlorite ion.
Cl2(aq) 2 OH(aq) 88n Cl(aq) OCl(aq) H2O(l )
Use this information to explain why people who make the mistake of mixing Clorox with hydrochloric acid often suffer damage to their lungs from breathing chlorine gas.
The Inorganic Chemistry of Carbon
78. Use the structure of graphite to explain why the bonds between carbon atoms are so strong that it is difficult to boil off individual carbon atoms, yet the material is so soft it can be used as a lubricant.
79. Explain why silicon forms a covalent carbide but calcium forms an ionic carbide.
80. Write balanced equations for the combustion of both CO and H2 that explain why a mixture of the gases can be used as a fuel.
81. Use Lewis structures to explain the following reaction.
CO2(g) H2O(l ) 88n H2CO3(aq)
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Integrated Problems
82. A recent catalog listed the following prices: $21.40 for 450 grams of sodium, $18.00 for 1 kilogram of zinc, and $52.80 for 250 grams of sodium hydride. Which reagent would be the least expensive source of H2gas?
83. A solution of hydrogen peroxide in water that is 30% hydrogen peroxide by weight sells for $15.95 per 500 g, and potassium chlorate sells for $12.75 per 500 grams. Is it less expensive to generate oxygen by decomposing H2O2or KClO3?
84. Write a sequence of reactions for the conversion of elemental nitrogen into nitric acid.
Calculate the weight of nitric acid that can be produced from a ton of nitrogen gas.
85. At 1700°C, P4molecules decompose partially to form P2. P4(g) 88n 2 P2(g)
If the average molecular weight of phosphorus at that temperature is 91 g/mol, what fraction of the P4 molecules decompose?
86. Uranium reacts with fluorine to form UF6, which boils at 51°C. The relative rate of diffusion of 235UF6 and 238UF6in the gas phase was used in the Manhattan project to separate the more abundant 238U isotope from 235U. Predict which substance diffuses more rapidly, and calculate the ratio of the rate of diffusion of the compounds.
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