2. Aqueous Reactions Chapter 4 Aqueous Reactions and Solution Stoichiometry John D. Bookstaver St. Charles Community College St. Peters, MO  2006, Prentice Hall, Inc. Chemistry, The Central Science, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten

3. Aqueous Reactions Solutions: Homogeneous mixtures of two or more pure substances. The solvent is present in greatest abundance. All other substances are solutes.

4. Aqueous Reactions Dissociation When an ionic substance dissolves in water, the solvent pulls the individual ions from the crystal and solvates them. This process is called dissociation.

5. Aqueous Reactions Electrolytes Substances that dissociate into ions when dissolved in water. A non-electrolyte may dissolve in water, but it does not dissociate into ions when it does so.

6. Aqueous Reactions Electrolytes and Nonelectrolytes Soluble ionic compounds tend to be electrolytes.

7. Aqueous Reactions Electrolytes and Nonelectrolytes Molecular compounds tend to be nonelectrolytes, except for acids and bases.

8. Aqueous Reactions Electrolytes A strong electrolyte dissociates completely when dissolved in water. A weak electrolyte only dissociates partially when dissolved in water.

9. Aqueous Reactions Strong Electrolytes Are… Strong acids

10. Aqueous Reactions Strong Electrolytes Are… Strong acids Strong bases

11. Aqueous Reactions Strong Electrolytes Are… Strong acids Strong bases Soluble ionic salts

12. Aqueous Reactions Precipitation Reactions When one mixes ions that form compounds that are insoluble (as could be predicted by the solubility guidelines), a precipitate is formed.

13. Aqueous Reactions Precipitation Reactions Common Solubility Laws (p. 127) Note: All common ionic compounds of the alkali metal ions, NH 4+, and NO 3 - are soluble in water

14. Aqueous Reactions Precipitation Reactions To predict whether a precipitate forms when two solutions of soluble aqueous compounds are mixed: 1.Note ions in the reactants 2.Consider all possible combinations (no +/+ or -/- combos) 3.Use table 4.1 to determine if any of these combinations are insoluble Ex: Mix Fe 2 (SO 4 ) 3 (aq) + LiOH (aq)

15. Aqueous Reactions Metathesis (Exchange) Reactions Metathesis comes from a Greek word that means “to transpose” AgNO 3 (aq) + KCl (aq)  AgCl (s) + KNO 3 (aq)

16. Aqueous Reactions Metathesis (Exchange) Reactions Metathesis comes from a Greek word that means “to transpose” It appears the ions in the reactant compounds exchange, or transpose, ions “Square-dancing” Switch your partners! AgNO 3 (aq) + KCl (aq)  AgCl (s) + KNO 3 (aq)

17. Aqueous Reactions Metathesis (Exchange) Reactions Metathesis comes from a Greek word that means “to transpose” It appears the ions in the reactant compounds exchange, or transpose, ions “Square-dancing” Switch your partners! AgNO 3 (aq) + KCl (aq)  AgCl (s) + KNO 3 (aq)

18. Aqueous Reactions Metathesis (Exchange) Reactions To complete and balance 1.Use chemical formulas of reactants to determine the ions that are present 2.Write the chemical formulas of products by rearranging and combining cations and anions 3.Balance the product chemical formulas 4.Balance the entire equation AgNO 3 (aq) + KCl (aq)  AgCl (s) + KNO 3 (aq)

19. Aqueous Reactions Solution Chemistry It is helpful to pay attention to exactly what species are present in a reaction mixture (i.e., solid, liquid, gas, aqueous solution). If we are to understand reactivity, we must be aware of just what is changing during the course of a reaction.

20. Aqueous Reactions Molecular Equation The molecular equation lists the reactants and products in their molecular form. Note that everything is aqueous, except the AgCl. What does that mean? AgNO 3 (aq) + KCl (aq)  AgCl (s) + KNO 3 (aq)

21. Aqueous Reactions Ionic Equation In the ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions. This more accurately reflects the species that are found in the reaction mixture. –Note: everything is broken up except the AgCl. Why? Ag + (aq) + NO 3 - (aq) + K + (aq) + Cl - (aq)  AgCl (s) + K + (aq) + NO 3 - (aq)

22. Aqueous Reactions Net Ionic Equation To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. Ag + (aq) + NO 3 - (aq) + K + (aq) + Cl - (aq)  AgCl (s) + K + (aq) + NO 3 - (aq)

23. Aqueous Reactions Net Ionic Equation To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. The only things left in the equation are those things that change (i.e., react) during the course of the reaction. Ag + (aq) + Cl - (aq)  AgCl (s)

24. Aqueous Reactions Net Ionic Equation To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. The only things left in the equation are those things that change (i.e., react) during the course of the reaction. Those things that didn’t change (and were deleted from the net ionic equation) are called spectator ions. Ag + (aq) + NO 3 - (aq) + K + (aq) + Cl - (aq)  AgCl (s) + K + (aq) + NO 3 - (aq)

25. Aqueous Reactions Writing Net Ionic Equations 1.Write a balanced molecular equation. 2.Dissociate all strong electrolytes. 3.Cross out anything that remains unchanged from the left side to the right side of the equation. 4.Write the net ionic equation with the species that remain.

26. Aqueous Reactions Writing Net Ionic Equations

27. Aqueous Reactions Stoichiometry – Determining the mass of a product formed 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.

28. Aqueous Reactions Stoichiometry – Determining the mass of a product formed When aqueous 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 0.0500 M Pb(NO 3 ) 2 & 2.00 L of 0.0250M Na 2 SO 4 are mixed.

29. Aqueous Reactions Acids: Neutralization Reactions Substances that increase the concentration of H + when dissolved in water (Arrhenius). Proton donors (Brønsted–Lowry).

30. Aqueous Reactions Acids There are only seven strong acids: Hydrochloric (HCl) Hydrobromic (HBr) Hydroiodic (HI) Nitric (HNO 3 ) Sulfuric (H 2 SO 4 ) Chloric (HClO 3 ) Perchloric (HClO 4 )

31. Aqueous Reactions Bases: Substances that increase the concentration of OH − when dissolved in water (Arrhenius). Proton acceptors (Brønsted–Lowry).

32. Aqueous Reactions Bases The strong bases are the soluble salts of hydroxide ion: Alkali metals Calcium Strontium Barium

33. Aqueous Reactions Acid-Base Reactions In an acid-base reaction, the acid donates a proton (H + ) to the base.

34. Aqueous Reactions Neutralization Reactions Generally, when solutions of an acid and a base are combined, the products are a salt and water. HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l)

35. Aqueous Reactions Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is… HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l) H + ( aq ) + Cl - ( aq ) + Na + ( aq ) + OH - ( aq )  Na + ( aq ) + Cl - ( aq ) + H 2 O ( l )

36. Aqueous Reactions Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is… HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l) H + ( aq ) + Cl - ( aq ) + Na + ( aq ) + OH - ( aq )  Na + ( aq ) + Cl - ( aq ) + H 2 O ( l ) H + ( aq ) + Cl - (aq) + Na + ( aq ) + OH - ( aq )  Na + ( aq ) + Cl - ( aq ) + H 2 O ( l )

37. Aqueous Reactions Neutralization Reactions Observe the reaction between Milk of Magnesia, Mg(OH) 2, and HCl.

38. Aqueous Reactions Gas-Forming Reactions These metathesis reactions do not give the product expected. The expected product decomposes to give a gaseous product (CO 2 or SO 2 ). CaCO 3 (s) + HCl (aq)  CaCl 2 (aq) + CO 2 (g) + H 2 O (l) NaHCO 3 (aq) + HBr (aq)  NaBr (aq) + CO 2 (g) + H 2 O (l) SrSO 3 (s) + 2 HI (aq)  SrI 2 (aq) + SO 2 (g) + H 2 O (l)

39. Aqueous Reactions Gas-Forming Reactions This reaction gives the predicted product, but you had better carry it out in the hood, or you will be very unpopular! Just as in the previous examples, a gas is formed as a product of this reaction: Na 2 S (aq) + H 2 SO 4 (aq)  Na 2 SO 4 (aq) + H 2 S (g)

40. Aqueous Reactions Neutralization reactions When volume of a 1.00 M HCl solution is needed to neutralize 25.0 mL of 0.350 M NaOH?

41. Aqueous Reactions Neutralization reactions In a certain experiment, 28.0 mL of 0.250 M HNO 3 and 53.0 mL of 0.320 M KOH are mixed. Calculate the amount of water formed in the resulting reaction. What is the concentration of H + or OH - s in excess after the reaction goes to completion?

42. Aqueous Reactions Titration The analytical technique in which one can calculate the concentration of a solute in a solution.

43. Aqueous Reactions Titration

44. Aqueous Reactions Neutralization reactions A student carries out an experiment to standardize a sodium hydroxide solution. To do this the student weighs out a 1.3009-g sample of potassium hydrogen phthalate or KHP(KHC 8 O 4 O 4. KHP (molar mass 204.22 g/mol) has one acidic hydrogen. The student dissolves the KHP in distilled water, adds phenolphthalein as an indicator, and titrates the resulting solution with the sodium hydroxide to the phenolphthalein endpoint. The difference between the final & initial buret readings indicates that 41.20 mL of the sodium hydroxide is required to react exactly with the 1.3009 g of KHP. Calculate the concentration of the sodium hydroxide solution.

45. Aqueous Reactions Neutralization reactions An environmental chemist analyzed the effluent from an industrial process known to produce the compounds carbon tetrachloride and benzoic acid (HC 7 H 5 O 2 ), a weak monoprotic acid. A sample of this effluent weighing 0.3518 g was shaken with water, and the resulting aqueous solution required 10.59 mL of 0.1546 M NaOH for neutralization. Calculate the mass percent of HC 7 H 5 O 2 in the original sample.

46. Aqueous Reactions Oxidation-Reduction Reactions An oxidation occurs when an atom or ion loses electrons. A reduction occurs when an atom or ion gains electrons.

47. Aqueous Reactions Oxidation-Reduction Reactions One cannot occur without the other.

48. Aqueous Reactions Terminology for Redox Reactions OXIDATION—loss of electron(s) by a species; increase in oxidation number; increase in oxygen.OXIDATION—loss of electron(s) by a species; increase in oxidation number; increase in oxygen. REDUCTION—gain of electron(s); decrease in oxidation number; decrease in oxygen; increase in hydrogen.REDUCTION—gain of electron(s); decrease in oxidation number; decrease in oxygen; increase in hydrogen. OXIDIZING AGENT—electron acceptor; species is reduced.OXIDIZING AGENT—electron acceptor; species is reduced. REDUCING AGENT—electron donor; species is oxidized.REDUCING AGENT—electron donor; species is oxidized. OXIDATION—loss of electron(s) by a species; increase in oxidation number; increase in oxygen.OXIDATION—loss of electron(s) by a species; increase in oxidation number; increase in oxygen. REDUCTION—gain of electron(s); decrease in oxidation number; decrease in oxygen; increase in hydrogen.REDUCTION—gain of electron(s); decrease in oxidation number; decrease in oxygen; increase in hydrogen. OXIDIZING AGENT—electron acceptor; species is reduced.OXIDIZING AGENT—electron acceptor; species is reduced. REDUCING AGENT—electron donor; species is oxidized.REDUCING AGENT—electron donor; species is oxidized. When you go to a travel agent, who ends up traveling? YOU, or the agent?

49. Aqueous Reactions You can’t have one… without the other! Reduction (gaining electrons) can’t happen without an oxidation to provide the electrons. You can’t have 2 oxidations or 2 reductions in the same equation. Reduction has to occur at the cost of oxidation LEO the lion says GER! o s e l e c t r o n s x i d a t i o n a i n l e c t r o n s e d u c t i o n GER!

50. Aqueous Reactions 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 4.4

51. Aqueous Reactions 4.4

52. Aqueous Reactions Disproportionation Reaction Cl 2 + 2OH - ClO - + Cl - + H 2 O Element is simultaneously oxidized and reduced. Types of Oxidation-Reduction Reactions Chlorine Chemistry 0 +1 4.4

53. Aqueous Reactions Chemistry in Action: Breath Analyzer 4.4 3CH 3 COOH + 2Cr 2 (SO 4 ) 3 + 2K 2 SO 4 + 11H 2 O 3CH 3 CH 2 OH + 2K 2 Cr 2 O 7 + 8H 2 SO 4 +6 +3

54. Aqueous Reactions 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

55. Aqueous Reactions Oxidation Numbers To determine if an oxidation-reduction reaction has occurred, we assign an oxidation number to each element in a neutral compound or charged entity.

56. Aqueous Reactions Oxidation Numbers Elements in their elemental form have an oxidation number of 0. The oxidation number of a monatomic ion is the same as its charge.

57. Aqueous Reactions Oxidation Numbers Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions.  Oxygen has an oxidation number of −2, except in the peroxide ion in which it has an oxidation number of −1.  Hydrogen is −1 when bonded to a metal, +1 when bonded to a nonmetal.

58. Aqueous Reactions Oxidation Numbers Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions.  Fluorine always has an oxidation number of −1.  The other halogens have an oxidation number of −1 when they are negative; they can have positive oxidation numbers, however, most notably in oxyanions.

59. Aqueous Reactions Oxidation Numbers The sum of the oxidation numbers in a neutral compound is 0. The sum of the oxidation numbers in a polyatomic ion is the charge on the ion. Analogous to the charge of an ion

60. Aqueous Reactions Oxidation-Reduction Reactions Metallurgy, the process of producing a metal from its ore, always involves oxidation-reduction reactions. In the metallurgy of gelena (PbS), the principle lead-containing ore, the first step is the conversion of lead sulfide to its oxide (a process called roasting): The oxide is the treated with carbon monoxide to produce the free metal: For each reaction, identify the atoms that are oxidized and reduced, specify the oxidizing and reducing agents.

61. Aqueous Reactions Figure 4.10 The oxidation numbers of elements in their compounds 4.4

62. Aqueous Reactions Replacement or Displacement Reactions In displacement reactions, ions oxidize an element. The ions, then, are reduced.

63. Aqueous Reactions Replacement or Displacement Reactions In this reaction, silver ions oxidize copper metal. Cu (s) + 2 Ag + (aq)  Cu 2+ (aq) + 2 Ag (s)

64. Aqueous Reactions Replacement or Displacement Reactions The reverse reaction, however, does not occur. Cu 2+ (aq) + 2 Ag (s)  Cu (s) + 2 Ag + (aq) x

65. Aqueous Reactions Activity Series

66. Aqueous Reactions Replacement or Displacement Reactions The Activity table allows us to predict whether a certain metal will be oxidized or not Top of table – the most easily oxidized “active” metals Any metal on the list can be oxidized by the ions of the elements below it.

67. Aqueous Reactions Replacement or Displacement Reactions Note that the Copper is above Silver on the Activity table Copper can be oxidized by Silver, not the reverse Cu 2+ (aq) + 2 Ag (s)  Cu (s) + 2 Ag + (aq) x

68. Aqueous Reactions Molarity – [Solution] Two solutions can contain the same compounds but be quite different because the proportions of those compounds are different. Molarity is one way to measure the concentration of a solution. moles of solute volume of solution in liters Molarity (M) =

69. Aqueous Reactions Molarity The greater the amount of solute dissolved in a certain amount of solvent, the more concentrated the resulting solution moles of solute volume of solution in liters Molarity (M) =

70. Aqueous Reactions Mixing a Solution

71. Aqueous Reactions Mixing a Solution How to make a 1.00 molar solution of CuSO 4 1.00 molar = 1.00 mole / 1 L Weigh out 1 mole of CuSO 4 Place in volumetric Flask qs with DI water

72. Aqueous Reactions Mixing a Solution How to make a 1.00 molar solution of CuSO 4 If using 0.250 L Flask – use 0.250 mole CuSO4 Weigh out 0.250 mole of CuSO 4 Place in volumetric Flask qs with DI water

73. Aqueous Reactions Dilution

74. Aqueous Reactions Mixing a Solution How to make dilutions from a stock solution Example – We need a 0.100 M CuSO4 solution from the 1.00 M solution.

75. Aqueous Reactions Using Molarities in Stoichiometric Calculations