1. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Chapter 4 Type of Chemical Reactions and Solution Stoichiometric Water, Nature of aqueous solutions, types of electrolytes, dilution. Types of chemical reactions: precipitation, acid-base and oxidation reactions. Stoichiometry of reactions and balancing the chemical equations.

2. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Aqueous Solutions Water is the dissolving medium, or solvent.

3. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 Figure 4.1: (Left) The water molecule is polar. (Right) A space-filling model of the water molecule.

4. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Figure 4.2: Polar water molecules interact with the positive and negative ions of a salt assisting in the dissolving process.

5. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Some Properties of Water 4 Water is “bent” or V-shaped. 4 The O-H bonds are covalent. 4 Water is a polar molecule. 4 Hydration occurs when salts dissolve in water.

6. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 Figure 4.3: (a) The ethanol molecule contains a polar O—H bond similar to those in the water molecule. (b) The polar water molecule interacts strongly with the polar O—H bond in ethanol. This is a case of "like dissolving like."

7. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 A Solute 4 dissolves in water (or other “solvent”) 4 changes phase (if different from the solvent) 4 is present in lesser amount (if the same phase as the solvent)

8. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 A Solvent 4 retains its phase (if different from the solute) 4 is present in greater amount (if the same phase as the solute)

9. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 General Rule for dissolution  Like dissolve like  Polar dissolve polar (water dissolve ethanol)  Non-polar dissolve nonpolar (benzene dissolve fat)

10. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Figure 4.5: When solid NaCl dissolves, the Na+ and Cl- ions are randomly dispersed in the water.

11. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Electrolytes Strong - conduct current efficiently NaCl, HNO 3 Weak - conduct only a small current vinegar, tap water Non - no current flows pure water, sugar solution

12. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Figure 4.4: Electrical conductivity of aqueous solutions.

13. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Acids Strong acids -dissociate completely to produce H + in solution hydrochloric and sulfuric acid HCl, H 2 SO 4 Weak acids - dissociate to a slight extent to give H + in solution acetic and formic acid CH 3 COOH, CH 2 O

14. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Bases Strong bases - react completely with water to give OH  ions. sodium hydroxide Weak bases - react only slightly with water to give OH  ions. ammonia

15. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Figure 4.6: HCl(aq) is completely ionized.

16. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 Figure 4.7: An aqueous solution of sodium hydroxide.

17. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 Figure 4.8: Acetic acid (HC 2 H 3 O 2 ) exists in water mostly as undissociated molecules. Only a small percentage of the molecules are ionized.

18. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 Molarity Molarity (M) = moles of solute per volume of solution in liters:

19. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 Sample Ex 4.1, 4.2, 4.3, 4.4 and 4.5 Molarity(M) = moles of solute Liters of solution Volume of solution(L) = moles of solute Molarity Moles of solute = M x volume of solution(L)

20. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20 Common Terms of Solution Concentration Stock - routinely used solutions prepared in concentrated form. Concentrated - relatively large ratio of solute to solvent. (5.0 M NaCl) Dilute - relatively small ratio of solute to solvent. (0.01 M NaCl): (MV) initial =(MV) Final

21. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 Figure 4.10: Steps involved in the preparation of a standard aqueous solution.

22. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 S.Ex. 4.7 What volume of 16M sulfuric acid must be used to prepare 1.5 L of a 0.10 M H 2 SO 4 solution? 1.5 L x 0.10 mol = 0.15 mol L solution V x 16 mol = 0.15 mol L solution V = 9.4x10 -3 L or 9.4 mL

23. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23 Figure 4.12: Dilution Procedure (a) A measuring pipet is used to transfer 28.7mL of 17.4 M acetic acid solution to a volumetric flask. (b) Water is added to the flask to the calibration mark. (c) The resulting solution is 1.00 M acetic acid.

24. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 24 Types of Solution Reactions 4 Precipitation reactions AgNO 3 (aq) + NaCl(aq)  AgCl(s) + NaNO 3 (aq) 4 Acid-base reactions NaOH(aq) + HCl(aq)  NaCl(aq) + H 2 O(l) 4 Oxidation-reduction reactions Fe 2 O 3 (s) + Al(s)  Fe(l) + Al 2 O 3 (s)

25. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 25 Figure 4.13: When yellow aqueous potassium chromate is added to a colorless barium nitrate solution, yellow barium chromate precipitates.

26. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 26 Simple Rules for Solubility 1.Most nitrate (NO 3  ) salts are soluble. 2.Most alkali (group 1A) salts and NH 4 + are soluble. 3.Most Cl , Br , and I  salts are soluble (NOT Ag +, Pb 2+, Hg 2 2+ ) 4.Most sulfate salts are soluble (NOT BaSO 4, PbSO 4, HgSO 4, CaSO 4 ) 5.Most OH  salts are only slightly soluble (NaOH, KOH are soluble, Ba(OH) 2, Ca(OH) 2 are marginally soluble) 6.Most S 2 , CO 3 2 , CrO 4 2 , PO 4 3  salts are only slightly soluble.

27. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 27 Describing Reactions in Solution Precipitation 1.Molecular equation (reactants and products as compounds) AgNO 3 (aq) + NaCl(aq)  AgCl(s) + NaNO 3 (aq) 2.Complete ionic equation (all strong electrolytes shown as ions) Ag + (aq) + NO 3 - (aq) + Na + (aq) +Cl  (aq)  AgCl(s) + Na + (aq) + NO 3 - (aq)

28. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 28 Describing Reactions in Solution (continued) 3.Net ionic equation (show only components that actually react) Ag + (aq) + Cl  (aq)  AgCl(s) Na + and NO 3  are spectator ions.

29. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 29 S Ex 4.8 i) KNO 3 + BaCl 2 ii) Na 2 SO4 + Pb(NO 3 ) 2 iii) KOH + Fe(NO 3 ) 3

30. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 30 Stoichiometry of Precipitation Rx S.ex.4.10: Calculate the mass of solid NaCl that must be added to 1.50 L of a 0.100 M AgNO 3 solution to precipitate all the Ag + in the form of AgCl Mixed solution contains the ions –Ag + NO 3- Na + Cl -

31. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 31 Figure 4.17 Molecular-Level Representations Illustrating the Reaction of KCl (aq) with AgNO 3 (aq) to Form AgCl (s)

32. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 32 Determining the Mass of Product Formed

33. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 33 Sample Ex. 4.11 When aq solutions of Na 2 SO 4 and Pb(NO 3 ) 2 are mixed PbSO 4 precipitates. Calculate the mass of PbSO 4 formed when 1.25 L of 0.00500 M Pb(NO 3 ) 2 and 2.00 L of 0.0250 M Na 2 SO 4 are mixed. Na 2 SO 4 + Pb(NO 3 ) 2 → PbSO 4 (s) + 2NaNO 3 Aqaqaq Net ionic reaction Pb 2+ (aq) + SO 4 2- → PbSO 4 (s) 0.0625 mol 0.0500 mol SO 4 2- is limiting. 0.0500 mol PbSO 4 (s) formed

34. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 34

35. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 35 Determinin g the Mass of Product Formed

36. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 36 Neutralization Reaction acid + base salt + water HCl (aq) + NaOH (aq) NaCl (aq) + H 2 OH + + Cl - + Na + + OH - Na + + Cl - + H 2 O H + + OH - H 2 O 4.3

37. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 37 Key Titration Terms Titrant - solution of known concentration used in titration Analyte - substance being analyzed Equivalence point - enough titrant added to react exactly with the analyte Endpoint - the indicator changes color so you can tell the equivalence point has been reached. movie

38. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 38 S. Ex 4.12 What volume of 0.100 M HCl solution is needed to neutralize 25.0 mL 0f 0.350 M NaOH? Na + + OH - + H + + Cl - = H 2 O + Na + + Cl - Net ionic; H + + OH - = H 2 O Moles of OH - =

39. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 39 Figure 4.18a-c The Titration of an Acid with a Base

40. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 40 4.12 Neutralization Reactions I

41. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 41 S.Ex 4.13 28.00 mL of 0.250 M HNO 3 mixed with 53.0 ml of 0.320 m KOH Calculate the amount of water formed. H + + NO 3 - K + + OH - Net ionic H + (aq) + OH - (aq) → H 2 O(l) 7.00x10 -3 1.70x10 -2 ??

42. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 42 S.Ex 4.13 Neutralization Reactions II

43. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 43 Performing Calculations for Acid-Base Reactions 1.List initial species and predict reaction. 2.Write balanced net ionic reaction. 3.Calculate moles of reactants. 4.Determine limiting reactant. 5.Calculate moles of required reactant/product. 6.Convert to grams or volume, as required. Remember: n H+ = n OH- (MV) H+ = (MV) OH-

44. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 44 S.Ex. 4.14 KHP(aq) +NaOH(aq) → H 2 O(l) +NaKP(aq) 1.3009 g 41.2 ml MM=204.22 Moles of KHP = 1.3009 / 204.22 = 6.3701x10 -3 mol 1 mole KHP : 1 mole NaOH 6.3701x10 -3 mol NaOH must be added, which is present in 0.0412 L of solution Molarity = mol NaOH = 6.3701x10 -3 mol = 0.155 M L solution0.0412 L

45. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 45 Oxidation-Reduction Reactions (electron transfer reactions) 2Mg (s) + O 2 (g) 2MgO (s) 2Mg 2Mg 2+ + 4e - O 2 + 4e - 2O 2- Oxidation half-reaction (lose e - ) Reduction half-reaction (gain e - ) 2Mg + O 2 + 4e - 2Mg 2+ + 2O 2- + 4e - 2Mg + O 2 2MgO

46. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 46 Redox Reactions Many practical or everyday examples of redox reactions: –Corrosion of iron (rust formation) –Forest fire –Charcoal grill –Natural gas burning –Batteries –Production of Al metal from Al 2 O 3 (alumina) –Metabolic processes combustion

47. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 47 Figure 4.19 The Reaction of Solid Sodium and Gaseous Chlorine to Form Solid Sodium Chloride

48. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 48 Oxidation of Copper Metal by Nitric Acid

49. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 49 Table 4.2 Rules for Assigning Oxidation States

50. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 50 NaIO 3 Na = +1 O = -2 3x(-2) + 1 + ? = 0 I = +5 IF 7 F = -1 7x(-1) + ? = 0 I = +7 K 2 Cr 2 O 7 O = -2K = +1 7x(-2) + 2x(+1) + 2x(?) = 0 Cr = +6 Oxidation numbers of all the elements in the following ? 4.4

51. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 51

52. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 52 4.17.Aluminum and Iodine Mix to Form Aluminum Iodide

53. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 53 Zn (s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu (s) Zn is oxidizedZn Zn 2+ + 2e - Cu 2+ is reducedCu 2+ + 2e - Cu Zn is the reducing agent Cu 2+ is the oxidizing agent 4.4 Copper wire reacts with silver nitrate to form silver metal. What is the oxidizing agent in the reaction? Cu (s) + 2AgNO 3 (aq) Cu(NO 3 ) 2 (aq) + 2Ag (s) Cu Cu 2+ + 2e - Ag + + 1e - AgAg + is reducedAg + is the oxidizing agent

54. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 54

55. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 55 Balancing by Half-Reaction Method 1.Write separate reduction, oxidation reactions. 2.For each half-reaction:  Balance elements (except H, O)  Balance O using H 2 O  Balance H using H +  Balance charge using electrons

56. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 56 Balancing by Half-Reaction Method (continued) 3.If necessary, multiply by integer to equalize electron count. 4.Add half-reactions. 5.Check that elements and charges are balanced.

57. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 57 Balancing Redox Equations Example: Balance the following redox reaction: Cr 2 O 7 2- + Fe 2+ Cr 3+ + Fe 3+ (acidic soln) 1) Break into half reactions: Cr 2 O 7 2- Cr 3+ Fe 2+ Fe 3+

58. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 58 Balancing Redox Equations 2) Balance each half reaction: Cr 2 O 7 2- Cr 3+ Cr 2 O 7 2- 2 Cr 3+ Cr 2 O 7 2- 2 Cr 3+ + 7 H 2 O Cr 2 O 7 2- + 14 H + 2 Cr 3+ + 7 H 2 O 6 e - + Cr 2 O 7 2- + 14 H + 2 Cr 3+ + 7 H 2 O

59. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 59 Balancing Redox Equations 2) Balance each half reaction (cont) Fe 2+ Fe 3+ Fe 2+ Fe 3+ + 1 e -

60. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 60 Balancing Redox Reactions 3) Multiply by integer so e - lost = e - gained 6 e - + Cr 2 O 7 2- + 14 H + 2 Cr 3+ + 7 H 2 O Fe 2+ Fe 3+ + 1 e - x 6

61. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 61 Balancing Redox Reactions 3) Multiply by integer so e - lost = e - gained 6 Fe 2+ 6 Fe 3+ + 6 e - 6 e - + Cr 2 O 7 2- + 14 H + 2 Cr 3+ + 7 H 2 O 4) Add both half reactions Cr 2 O 7 2- + 6 Fe 2+ + 14 H + 2 Cr 3+ + 6 Fe 3+ + 7 H 2 O

62. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 62 Balancing Redox Reactions Cr 2 O 7 2- + 6 Fe 2+ + 14 H + 2 Cr 3+ + 6 Fe 3+ + 7 H 2 O 5) Check the equation 2 Cr7 O6 Fe14 H +24 + 24

63. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 63 MnO 4 - + Fe 2+ → Fe 3+ + Mn 2+ MnO 4 - → Mn 2+ Fe 2+ → Fe 3+

64. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 64 4.19.When Potassium Dichromate Reacts with Ethanol, the Solution Contains Cr 3+.

65. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 65 Half-Reaction Method - Balancing in Base 1.Balance as in acid. 2.Add OH  that equals H + ions (both sides!) 3.Form water by combining H +, OH . 4.Check elements and charges for balance.

66. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 66 Balancing Redox Reactions Procedure for Basic Solutions: –Divide the equation into 2 incomplete half reactions one for oxidation one for reduction

67. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 67 Balancing Redox Reactions –Balance each half-reaction: balance elements except H and O balance O atoms by adding H 2 O balance H atoms by adding H + add 1 OH - to both sides for every H + added combine H + and OH - on same side to make H 2 O cancel the same # of H 2 O from each side balance charge by adding e - to side with greater overall + charge different

68. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 68 Balancing Redox Equations –Multiply each half reaction by an integer so that # e - lost = # e - gained –Add the half reactions together. Simply where possible by canceling species appearing on both sides of equation –Check the equation # of atoms total charge on each side

69. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 69 Balancing Redox Reactions Example: Balance the following redox reaction. NH 3 + ClO - Cl 2 + N 2 H 4 (basic soln) NH 3 N 2 H 4 ClO - Cl 2 1) Break into half reactions:

70. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 70 Balancing Redox Reactions NH 3 N 2 H 4 2) Balance each half reaction: 2 NH 3 N 2 H 4 2 NH 3 N 2 H 4 + 2 H + 2 NH 3 + 2 OH - N 2 H 4 + 2 H 2 O + 2 OH - + 2 OH - 2H2O2H2O 2 NH 3 + 2 OH - N 2 H 4 + 2 H 2 O + 2 e -

71. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 71 Balancing Redox Reactions 2 ClO - Cl 2 2) Balance each half reaction: 2 ClO - Cl 2 + 2 H 2 O 2 ClO - + 4 H + Cl 2 + 2 H 2 O + 4 OH - + 4 OH - 2 ClO - + 4 H 2 O Cl 2 + 2 H 2 O + 4 OH - 2 ClO - + 2 H 2 O Cl 2 + 4 OH - 2 e - + 2 ClO - + 2 H 2 O Cl 2 + 4 OH - ClO - Cl 2

72. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 72 Balancing Redox Reactions 3) Multiply by integer so # e - lost = # e - gained 2 NH 3 + 2 OH - N 2 H 4 + 2 H 2 O + 2 e - 2 e - + 2 ClO - + 2 H 2 O Cl 2 + 4 OH - 4) Add both half reactions 2 NH 3 + 2 OH - + 2ClO - + 2 H 2 O N 2 H 4 + 2 H 2 O + Cl 2 + 4 OH -

73. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 73 Balancing Redox Reactions 5) Cancel out common species 2 NH 3 + 2 OH - + 2 ClO - + 2 H 2 O N 2 H 4 + 2 H 2 O + Cl 2 + 4 OH - 2 2 NH 3 + 2 ClO - N 2 H 4 + Cl 2 + 2 OH - 6) Check final equation: 2 N6 H2 Cl2 O-2

74. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 74

75. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 75

76. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 76 Practice Example In the following the oxidizing agent is: 5H 2 O 2 + 2MnO 4 - + 6H +  2Mn 2+ + 8H 2 O + 5O 2 a. MnO 4 - b. H 2 O 2 c. H + d. Mn 2+ e. O 2

77. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 77 Practice Example Determine the coefficient of Sn in acidic solution Sn + HNO 3  SnO 2 + NO 2 + H 2 O 1

78. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 78 Practice Example Consider the reaction N 2 + 3H 2 = 2NH 3 How many moles of H 2 are needed to completely react 56 g of N 2 ?

79. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 79 Practice Example How many grams are in 0.0150 mole of caffeine C 8 H 10 N 4 O 2

80. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 80 Practice Example The sum of the coefficients when they are whole numbers in basic solution: Bi(OH) 3 + SnO 2 2-  Bi + SnO 3 2- 13

81. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 81 http://www.chemistrycoach.com/balancing_redox_in_acid.htm#Bal ancingRedoxEquationsinAcidicorBasicMedium

82. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 82 Practice Example How many moles are in 18.2 g of CO 2 ?

83. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 83 http://www.chemistrycoach.com/tutorials-5.htm#Oxidation-Reduction

84. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 84 Practice Example A solution containing Ni 2+ is prepared by dissolving 1.485 g of pure nickel in nitric acid and diluting to 1.00 L. A 10.00 mL aliquot is then diluted to 500.0 mL. What is the molarity of the final solution? (Atomic weight: Ni = 58.70).

85. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 85 Practice Example What is the mass percent of hydrogen in acetic acid HC 2 H 3 O 2

86. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 86 Practice Example Calculate the number of molecules of vitamin A, C 20 H 30 O in 1.5 mg of this compound.