1. Reactions in Aqueous Solution Chapter 4

2. Solutions solute + solvent -Solute present in smaller amount -Solvent in larger amount -Can be gaseous, solid (alloy), or liquid (sea water)

3. Aqueous Solutions Solvent is water Solute: liquid or solid, (gas?) Properties – General Electrolytes and non electrolytes -Electrolytes in water conducts electricity -Nonelectrolytes does not conduct electricity -Light bulb illumination of ionic compds. in water because of +ve and –ve ion formation

4. An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity. A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct electricity. nonelectrolyte weak electrolyte strong electrolyte

5. Ions in Aqueous Solution Many ionic compounds dissociate into independent ions when dissolved in water Ionic Theory of Solutions These compounds that “freely” dissociate into independent ions in aqueous solution are called electrolytes. Their aqueous solutions are capable of conducting an electric current.

6. Ions in Aqueous Solution Not all electrolytes are ionic compounds. Some molecular compounds dissociate into ions. Ionic Theory of Solutions The resulting solution is electrically conducting, and so we say that the molecular substance is an electrolyte.

7. Ions in Aqueous Solution Strong and weak electrolytes. A strong electrolyte is an electrolyte that exists in solution almost entirely as ions. Most ionic solids that dissolve in water do so almost completely as ions, so they are strong electrolytes. Ionic Theory of Solutions

8. Ions in Aqueous Solution Strong and weak electrolytes. A weak electrolyte is an electrolyte that dissolves in water to give a relatively small percentage of ions. Double arrow represents not complete reaction, another example, CH 3 COOH Most soluble molecular compounds are either nonelectrolytes or weak electrolytes. Ionic Theory of Solutions

9. Ionization of acetic acid CH 3 COOH CH 3 COO - (aq) + H + (aq) A reversible reaction. The reaction can occur in both directions. Acetic acid is a weak electrolyte because its ionization in water is incomplete.

10. Hydration is the process in which an ion is surrounded by water molecules arranged in a specific manner.   H2OH2O

11. Types of Chemical Reactions Precipitation Reactions A precipitation reaction occurs in aqueous solution because one product is insoluble. A precipitate is an insoluble solid compound formed during a chemical reaction in solution. For example, the reaction of sodium chloride with silver nitrate forms AgCl (s), an insoluble precipitate.

12. Precipitation Reactions Precipitate – insoluble solid that separates from solution molecular equation ionic equation net ionic equation Pb 2+ (aq) + 2NO 3 - (aq) + 2Na + (aq) + 2I - (aq) PbI 2 (s) + 2Na + (aq) + 2NO 3 - (aq) Na + and NO 3 - are spectator ions PbI 2 Pb(NO 3 ) 2 (aq) + 2NaI (aq) PbI 2 (s) + 2NaNO 3 (aq) precipitate Pb 2+ (aq) + 2I - (aq) PbI 2 (s)

13. Precipitation of Lead Iodide PbI 2 Pb 2+ + 2I - PbI 2 (s)

14. Ions in Aqueous Solution A molecular equation is one in which the reactants and products are written as if they were molecules, even though they may actually exist in solution as ions. Pb(NO 3 ) 2 (aq) + 2NaI (aq) → PbI 2 (s) + 2NaNO 3 (aq) Molecular and Ionic Equations

15. Ions in Aqueous Solution An ionic equation, however, represents strong electrolytes as separate independent ions. This is a more accurate representation of the way electrolytes behave in solution. Pb 2+ (aq) + 2NO 3 - (aq) + 2Na + (aq) + 2I - (aq) → PbI 2 (s) + 2Na + (aq) + 2NO 3 - (aq) Molecular and Ionic Equations

16. Ions in Aqueous Solution Complete and net ionic equations. Molecular and Ionic Equations A net ionic equation is a chemical equation from which the spectator ions have been removed. Pb 2+ (aq) + 2I - (aq) → PbI 2 (s) A spectator ion is an ion in an ionic equation that does not take part in the reaction. 2 Na+(aq)+ 2 NO 3 - (aq) → 2 Na + (aq)+ 2 NO 3 - (aq)

17. Solubility is the maximum amount of solute that will dissolve in a given quantity of solvent at a specific temperature. (insoluble ) (soluble)

19. Chemistry In Action: p.126 CO 2 (aq) CO 2 (g) Ca 2+ (aq) + 2HCO 3 (aq) CaCO 3 (s) + CO 2 (aq) + H 2 O (l) - An Undesirable Precipitation Reaction (HCO 3 from dissolved CO 2 in water with CO 3 2- )

20. Acid-Base Reactions Acids Have a sour taste. Vinegar owes its taste to acetic acid. Citrus fruits contain citric acid. React with certain metals to produce hydrogen gas. React with carbonates and bicarbonates to produce carbon dioxide gas Cause color changes in plant dyes. 2HCl (aq) + Mg (s) MgCl 2 (aq) + H 2 (g) 2HCl (aq) + CaCO 3 (s) CaCl 2 (aq) + CO 2 (g) + H 2 O (l) Aqueous acid solutions conduct electricity.

21. Have a bitter taste. Feel slippery. Many soaps contain bases. Bases Aqueous base solutions conduct electricity.

22. Types of Chemical Reactions The Arrhenius Concept Acid-Base Reactions The Arrhenius concept defines acids as substances that produce hydrogen ions, H +, when dissolved in water. An example is nitric acid, HNO 3, a molecular substance that dissolves in water to give H + and NO 3 -.

23. Types of Chemical Reactions Acid-Base Reactions The Arrhenius concept defines bases as substances that produce hydroxide ions, OH -, when dissolved in water. An example is sodium hydroxide, NaOH, an ionic substance that dissolves in water to give sodium ions and hydroxide ions. The Arrhenius Concept

24. Arrhenius acid is a substance that produces H + (H 3 O + ) in water Arrhenius base is a substance that produces OH - in water

25. Types of Chemical Reactions Acid-Base Reactions –The Arrhenius concept acid: proton (H + ) donor base: hydroxide ion (OH - ) donor Bronsted-Lowry concept: Acid: proton donor, Base: proton acceptor In summary, both concepts the same

26. Identify each of the following species as a Brønsted acid, base, or both. (a) HI, (b) CH 3 COO -, (c) H 2 PO 4 - HI (aq) H + (aq) + I - (aq)Brønsted acid CH 3 COO - (aq) + H + (aq) CH 3 COOH (aq)Brønsted base H 2 PO 4 - (aq) H + (aq) + HPO 4 2- (aq) H 2 PO 4 - (aq) + H + (aq) H 3 PO 4 (aq) Brønsted acid Brønsted base

27. Types of Chemical Reactions Acid-Base Reactions Strong and Weak Acids and Bases A strong acid is an acid that ionizes completely in water; it is a strong electrolyte.

28. Types of Chemical Reactions Acid-Base Reactions Strong and Weak Acids and Bases A weak acid is an acid that only partially ionizes in water; it is a weak electrolyte. The hydrogen cyanide molecule, HCN, reacts with water to produce a small percentage of ions in solution.

29. Types of Chemical Reactions Acid-Base Reactions Strong and Weak Acids and Bases A strong base is a base that is present entirely as ions, one of which is OH - ; it is a strong electrolyte. The hydroxides of Group IA and IIA elements, except for beryllium hydroxide, are strong bases.

30. Types of Chemical Reactions Acid-Base Reactions Strong and Weak Acids and Bases A weak base is a base that is only partially ionized in water; it is a weak electrolyte. Ammonia, NH 3, is an example.

31. Table 4.3

32. Monoprotic acids HCl H + + Cl - HNO 3 H + + NO 3 - CH 3 COOH H + + CH 3 COO - Strong electrolyte, strong acid Weak electrolyte, weak acid Diprotic acids H 2 SO 4 H + + HSO 4 - HSO 4 - H + + SO 4 2- Strong electrolyte, strong acid Weak electrolyte, weak acid Triprotic acids H 3 PO 4 H + + H 2 PO 4 - H 2 PO 4 - H + + HPO 4 2- HPO 4 2- H + + PO 4 3- Weak electrolyte, weak acid

33. Neutralization Reaction acid + base salt + water HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O H + + Cl - + Na + + OH - Na + + Cl - + H 2 O H + + OH - H 2 O

34. Types of Chemical Reactions Acid-Base Reactions Neutralization Reactions Canceling the spectator ions results in the net ionic equation. Note the proton transfer. H+H+

35. Types of Chemical Reactions Sulfides react with acids to form H 2 S, hydrogen sulfide gas. Na 2 S + 2HCl→ 2NaCl+H 2 S Carbonates react with acids to form CO 2, carbon dioxide gas. Sulfites react with acids to form SO 2, sulfur dioxide gas.

36. Types of Chemical Reactions Oxidation-Reduction Reactions Oxidation-reduction reactions involve the transfer of electrons from one species to another. Oxidation is defined as the loss of electrons. Reduction is defined as the gain of electrons. Oxidation and reduction always occur simultaneously.

37. 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 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

38. Oxidation-Reduction Reactions (electron transfer reactions) 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

39. Types of Chemical Reactions Oxidation-Reduction Reactions The reaction of an iron nail with a solution of copper(II) sulfate, CuSO 4, is an oxidation- reduction reaction The molecular equation for this reaction is:

40. Types of Chemical Reactions Oxidation-Reduction Reactions The net ionic equation shows the reaction of iron metal with Cu 2+ (aq) to produce iron(II) ion and copper metal. Loss of 2 e -1 oxidation Gain of 2 e -1 reduction

41. Types of Chemical Reactions Describing Oxidation-Reduction Reactions Oxidation-Reduction Reactions Look again at the reaction of iron with copper(II) sulfate. We can write this reaction in terms of two half-reactions.

42. Types of Chemical Reactions Describing Oxidation-Reduction Reactions Oxidation-Reduction Reactions A half-reaction is one of the two parts of an oxidation-reduction reaction. One involves the loss of electrons (oxidation) and the other involves the gain of electrons (reduction). oxidation half-reaction reduction half-reaction

43. Types of Chemical Reactions Describing Oxidation-Reduction Reactions Oxidation-Reduction Reactions An oxidizing agent is a species that oxidizes another species; it is itself reduced. A reducing agent is a species that reduces another species; it is itself oxidized. oxidizing agent reducing agent Loss of 2 e - oxidation Gain of 2 e - reduction

44. Types of Chemical Reactions Oxidation Numbers The concept of oxidation numbers is a simple way of keeping track of electrons in a reaction. The oxidation number (or oxidation state) of an atom in a substance is the actual charge of the atom if it exists as a monatomic ion. Alternatively, it is hypothetical charge assigned to the atom in the substance by simple rules. Oxidation-Reduction Reactions

45. Types of Chemical Reactions Oxidation Number Rules Oxidation-Reduction Reactions RuleApplies toStatement 1ElementsThe oxidation number of an atom in an element is zero. 2Monatomic ions The oxidation number of an atom in a monatomic ion equals the charge of the ion. 3OxygenThe oxidation number of oxygen is –2 in most of its compounds. (An exception is O in H 2 O 2 and other peroxides, where the oxidation number is –1.) In compounds or molecules,

46. Types of Chemical Reactions Oxidation Number Rules Oxidation-Reduction Reactions RuleApplies toStatement 4HydrogenThe oxidation number of hydrogen is +1 except when it is bonded to metals in binary compounds, where it is -1, eg. LiH 5HalogensFluorine is –1 in all its compounds. Each of the other halogens is –1 in binary compounds unless the other element is oxygen. 6Compounds and ions The sum of the oxidation numbers of the atoms in a compound is zero. The sum in a polyatomic ion equals the charge on the ion.

47. Oxidation number (Do ex.4.5) The charge the atom would have in a molecule (or an ionic compound) if electrons were completely transferred. 1.Free elements (uncombined state) have an oxidation number of zero. Na, Be, K, Pb, H 2, O 2, P 4 = 0 2.In monatomic ions, the oxidation number is equal to the charge on the ion. Li +, Li = +1; Fe 3+, Fe = +3; O 2-, O = -2 3.The oxidation number of oxygen is usually –2. In H 2 O 2 and O 2 2- it is –1.

48. Types of Oxidation-Reduction Reactions Combination Reaction A + B C 2Al + 3Br 2 2AlBr 3 00 +3 Al lost electrons – oxidized Br gained electrons - reduced

49. Types of Oxidation-Reduction Reactions Decomposition Reaction 2KClO 3 2KCl + 3O 2 C A + B +1+5-2+10

50. Types of Oxidation-Reduction Reactions Combustion Reaction A + O 2 B S + O 2 SO 2 00 +4-2 2Mg + O 2 2MgO 00 +2-2

51. Displacement Reaction A + BC AC + B Sr + 2H 2 O Sr(OH) 2 + H 2 TiCl 4 + 2Mg Ti + 2MgCl 2 Cl 2 + 2KBr 2KCl + Br 2 Hydrogen Displacement Metal Displacement Halogen Displacement Types of Oxidation-Reduction Reactions 0 +1+20 0+40+2 0 0

52. The Activity Series for Halogens Halogen Displacement Reaction Cl 2 + 2KBr 2KCl + Br 2 0 0 F 2 > Cl 2 > Br 2 > I 2 I 2 + 2KBr 2KI + Br 2

53. The Activity Series for Metals M + BC AC + B Hydrogen Displacement Reaction M is metal BC is acid or H 2 O B is H 2 Ca + 2H 2 O Ca(OH) 2 + H 2 Pb + 2H 2 O Pb(OH) 2 + H 2

54. Types of Chemical Reactions Balancing Simple Oxidation-Reduction Reactions Oxidation-Reduction Reactions Since the number of electrons lost in the oxidation half-reaction must equal the number gained in the reduction half- reaction, we must double the reaction involving the reduction of the silver. oxidation half-reaction reduction half-reaction 2 2 2

55. Types of Chemical Reactions Balancing Simple Oxidation-Reduction Reactions Oxidation-Reduction Reactions Adding the two half-reactions together, the electrons cancel, oxidation half-reaction reduction half-reaction which yields the balanced oxidation-reduction reaction.

56. Working with Solutions Molar concentration, or molarity (M), is defined as the moles of solute dissolved in one liter (cubic decimeter) of solution. Molar Concentration

57. Solution Stoichiometry The concentration of a solution is the amount of solute present in a given quantity of solvent or solution. M = molarity = moles of solute liters of solution What mass of KI is required to make 500. mL of a 2.80 M KI solution? volume of KI solutionmoles KIgrams KI M KI 500. mL= 232 g KI 166 g KI 1 mol KI x 2.80 mol KI 1 L soln x 1 L 1000 mL x

58. 4.5

59. Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution. Dilution Add Solvent Moles of solute before dilution (i) Moles of solute after dilution (f) = MiViMiVi MfVfMfVf =

60. How would you prepare 60.0 mL of 0.200 M HNO 3 from a stock solution of 4.00 M HNO 3 ? M i V i = M f V f M i = 4.00 M f = 0.200V f = 0.06 L V i = ? L V i = MfVfMfVf MiMi = 0.200 x 0.06 4.00 = 0.003 L = 3 mL 3 mL of acid + 57 mL of water= 60 mL of solution

61. Quantitative Analysis Analytical chemistry deals with the determination of composition of materials- that is, the analysis of materials. Quantitative analysis involves the determination of the amount of a substance or species present in a material.

62. Quantitative Analysis Gravimetric analysis is a type of quantitative analysis in which the amount of a species in a material is determined by converting the species into a product that can be isolated and weighed. Precipitation reactions are often used in gravimetric analysis. The precipitate from these reactions is then filtered, dried, and weighed. Gravimetric Analysis

63. Quantitative Analysis Consider the problem of determining the amount of lead in a sample of drinking water. Gravimetric Analysis Adding sodium sulfate (Na 2 SO 4 ) to the sample will precipitate lead(II) sulfate. The PbSO 4 can then be filtered, dried, and weighed.

64. Quantitative Analysis Suppose a 1.00 L sample of polluted water was analyzed for lead(II) ion, Pb 2+, by adding an excess of sodium sulfate to it. The mass of lead(II) sulfate that precipitated was 229.8 mg. What is the mass of lead in a liter of the water? Express the answer as mg of lead per liter of solution. Gravimetric Analysis

65. Quantitative Analysis Gravimetric Analysis First we must obtain the mass percentage of lead in lead(II) sulfate, by dividing the molar mass of lead by the molar mass of PbSO 4, then multiplying by 100. PbSO 4 Then, calculate the amount of lead in the PbSO 4 precipitated. Pb

66. Quantitative Analysis Volumetric Analysis An important method for determining the amount of a particular substance is based on measuring the volume of the reactant solution. Titration is a procedure for determining the amount of substance A by adding a carefully measured volume of a solution with known concentration of B until the reaction of A and B is just complete. Volumetric analysis is a method of analysis based on titration.

67. Quantitative Analysis Volumetric Analysis An important method for determining the amount of a particular substance is based on measuring the volume of the reactant solution. Titration is a procedure for determining the amount of substance A by adding a carefully measured volume of a solution with known concentration of B until the reaction of A and B is just complete. Volumetric analysis is a method of analysis based on titration.

68. Titrations In a titration, a solution of accurately known concentration is added gradually to another solution of unknown concentration until the chemical reaction between the two solutions is complete. Equivalence point – the point at which the reaction is complete Indicator – substance that changes color at (or near) the equivalence point Slowly add base to unknown acid UNTIL the indicator changes color

69. What volume of a 1.420 M NaOH solution is Required to titrate 25.00 mL of a 4.50 M H 2 SO 4 solution? WRITE THE CHEMICAL EQUATION! volume acidmoles acidmoles basevolume base H 2 SO 4 + 2NaOH 2H 2 O + Na 2 SO 4 4.50 mol H 2 SO 4 1000 mL soln x 2 mol NaOH 1 mol H 2 SO 4 x 1000 ml soln 1.420 mol NaOH x 25.00 mL = 158 mL M acid rx coef. M base

70. Moles of acid = (4.5 moles/1000 mL) x 25 mL= 0.1125 moles 1mol of acid equivalent to 2 moles of NaOH, (2 mols of NaOH/1 mol acid) x 0.1125 moles of acid = 0.225 moles of NaOH 0.225moles of base x1000 mL base/1.42 moles = 158.45 mL

71. Quantitative Analysis Volumetric Analysis Consider the reaction of sulfuric acid, H 2 SO 4, with sodium hydroxide, NaOH: Suppose a beaker contains 35.0 mL of 0.175 M H 2 SO 4. How many milliliters of 0.250 M NaOH must be added to completely react with the sulfuric acid?

72. Quantitative Analysis Volumetric Analysis First we must convert the 0.0350 L (35.0 mL) to moles of H 2 SO 4 (using the molarity of the H 2 SO 4 ). Then, convert to moles of NaOH (from the balanced chemical equation). Finally, convert to volume of NaOH solution (using the molarity of NaOH).

73. Chemical Reactions Reactions often involve ions in aqueous solution. Many of these compounds are electrolytes. We can represent these reactions as molecular equations, complete ionic equations (with strong electrolytes represented as ions), or net ionic equations (where spectator ions have been canceled). Most reactions are either precipitation reactions, acid-base reactions, or oxidation-reduction reactions. Acid-base reactions are proton-transfer reactions. Oxidation-reduction reactions involve a transfer of electrons from one species to another. Summary

74. Chemical Reactions Oxidation-reduction reactions usually fall into the following categories: combination reactions, decomposition reactions, displacement reactions, and combustion reactions. Molarity is defined as the number of moles of solute per liter of solution. Knowing the molarity allows you to calculate the amount of solute in a given volume of solution. Quantitative analysis involves the determination of the amount of a species in a material. Summary

75. Chemical Reactions In gravimetric analysis, you determine the amount of a species by converting it to a product you can weigh. Summary In volumetric analysis, you determine the amount of a species by titration.

76. Operational Skills Using solubility rules. Writing net ionic equations. Deciding whether precipitation occurs. Classifying acids and bases as weak or strong. Writing an equation for a neutralization. Writing an equation for a reaction with gas formation. Assigning oxidation numbers. Balancing simple oxidation-reduction reactions. Calculating molarity from mass and volume. Using molarity as a conversion factor. Diluting a solution. Determining the amount of a substance by gravimetric analysis. Calculating the volume of reactant solution needed. Calculating the quantity of a substance by titration.

77. Homework ch-4 Practice all the example problems 4.1,4.2,4.6,4.10,4.17,4.18,4.22,4.34,4.40,4.44, 4.54,4.62,4.65,4.75,4.78,4.81,4.84,4.90,4.96