Copyright©2004 by houghton Mifflin Company. All rights reserved. 1 Introductory Chemistry: A Foundation FIFTH EDITION by Steven S. Zumdahl University of Illinois

2 Reactions in Aqueous Solutions Chapter 7

3 Precipitation Reactions in all precipitation reactions, the ions of one substance are exchanged with the ions of another substance when their aqueous solutions are mixed At least one of the products formed is insoluble in water KI(aq) + AgNO 3 (aq)  KNO 3 (aq) + AgI  s  K+K+ I-I- Ag + NO 3 - K+K+ Ag I

4 Overview In Chapter 7, our goals are for the students to: 1. Learn about some of the factors that cause reactions to occur. 2. Learn to identify the solid that forms in a precipitation reaction. 3. Learn to describe reactions in solution by writing molecular, complete, ionic, and net ionic equations. 4. Learn the key characteristics of reactions between strong acids and strong bases. 5. Learn the general characteristics of reactions between metals and nonmetals. 6. Understand electron transfer as a driving force for a chemical reaction. 7. Learn various classification schemes for reactions. 8. Consider additional classes of chemical reactions.

5 Predicting Whether a Reaction Will Occur Forces that drive a reaction formation of a solid (precipitate) formation of water transfer of electrons formation of a gas when chemicals (dissolved in water) are mixed and one of these 4 things can occur, the reaction will generally happen

What happens when an ionic compound dissolves in water? Ba(NO 3 ) 2 (aq) means barium nitrate has been dissolved in water Note: barium nitrate contains Ba 2+ ions and NO 3 - ions In many cases, when a solid containing ions dissolves in water, the ions separate and move around independently 6 Ba 2+ NO 3 -

7 Dissociation ionic compounds –metal + nonmetal (Type I & II) –metal + polyatomic anion –polyatomic cation + anion when ionic compounds dissolve in water the anions and cations are separated from each other; this is called dissociation we know that ionic compounds dissociate when they dissolve in water because the solution conducts electricity

8 Dissociation potassium chloride dissociates in water into potassium cations and chloride anions KCl(aq) = K + (aq) + Cl - (aq) copper(II) sulfate dissociates in water into copper(II) cations and sulfate anions CuSO 4 (aq) = Cu +2 (aq) + SO 4 2- (aq) K+K+ Cl - K Cl Cu +2 SO 4 2- Cu SO 4

9 Dissociation potassium sulfate dissociates in water into potassium cations and sulfate anions K 2 SO 4 (aq) = 2 K + (aq) + SO 4 2- (aq) K+K+ SO 4 2- K+K+ KK SO 4

10 Strong Electrolytes Any compound that dissolves (dissociates) in water produces separated ions, the substance is called a strong electrolyte. - Examples: KCl, CuSO 4 electrolytes are substances whose aqueous solution is a conductor of electricity in strong electrolytes, virtually all the molecules are dissociated into ions

11 Weak Electrolytes and Nonelectrolytes in nonelectrolytes, none of the molecules are dissociated into ions in weak electrolytes, a small percentage of the molecules are dissociated into ions

12 Figure 7.2: Electrical conductivity of aqueous solutions. (a) Pure water does not conduct an electric current. (b) When an ionic compound is dissolved in water, current flows and the lamp lights.

Video VzLwYhttps:// VzLwY 13

14 Process for Predicting the Products of a Precipitation Reaction ¬Determine what ions each aqueous reactant has ­Exchange Ions –(+) ion from one reactant with (-) ion from other ®Balance Charges of combined ions to get formula of each product ¯Balance the Equation –count atoms °Determine Solubility of Each Product in Water –solubility rules –if product is insoluble or slightly soluble, it will precipitate

Predicting the Formation of a Precipitate How can you predict the formation of a precipitate in a double-replacement reaction? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The mixing of two solutions can sometimes result in the formation of an insoluble salt called a precipitate. - We use solubility rules to determine which product is the precipitate

Solubility Rules for Ionic Compounds CompoundsSolubilityExceptions Salts of alkali metals and ammonia SolubleSome lithium compounds Nitrate salts and chlorate salts SolubleFew exceptions Sulfate saltsSoluble Compounds of Pb, Ag, Hg, Ba, Sr, and Ca Chloride saltsSoluble Compounds of Ag and some compounds of Hg and Pb Carbonates, phosphates, chromates, sulfides, and hydroxides Most are insoluble Compounds of the alkali metals and of ammonia Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Interpret Data

Will a precipitate form when aqueous solutions of Na 2 CO 3 (aq) and Ba(NO 3 ) 2 (aq) are mixed? Na 2 CO 3 (aq) + Ba(NO 3 ) 2 (aq) → Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Predicting the Formation of a Precipitate

18 Describing Reactions in Aqueous Solutions AIM: Learn to describe reactions in solution by writing molecular, complete, ionic, and net ionic equations.

19 Describing Reactions in Aqueous Solutions Molecular Equations An equation showing the reactants and products in undissociated form Identify as solid (s), gas (g), liquid (l) or dissolved (aq) KCl(aq) + AgNO 3 (aq)  KNO 3 (aq) + AgCl(s)

20 Describing Reactions in Aqueous Solutions Ionic Equations An equation that shows all dissolved substances as ions (except for weak electrolytes and nonelectrolytes) K + (aq) + Cl - (aq) + Ag + (aq) + NO 3 - (aq)  K + (aq) + NO 3 - (aq) + AgCl (s)

21 Net Ionic Equations ions that are both reactants and products are called spectator ions K + (aq) + Cl - (aq) + Ag + (aq) + NO 3 - (aq)  K + (aq) + NO 3 - (aq) + AgCl(s) an ionic equation in which the spectator ions are dropped is called a net ionic equation Cl - (aq) + Ag + (aq)  AgCl(s)

22 Describing Reactions in Solution Precipitation 1.Write the molecular equation, ionic equation, and net ionic equation for the reaction below. Identify spectator ions. Rubidium hydroxide (aq) reacts with calcium chloride (aq) to produce 

23 Describing Reactions in Solution Precipitation 1.Molecular equation (reactants and products as compounds) 2RbOH(aq) + CaCl 2 (aq)  Ca(OH) 2 (s) + 2RbCl(aq) 2.Complete ionic equation (all strong electrolytes shown as ions) 2Rb + (aq) + 2OH - (aq) + Ca + (aq) + 2Cl - (aq)  Ca(OH) 2 (s) + 2Rb + (aq) + 2Cl - (aq)

24 Describing Reactions in Solution (continued) 3. Net ionic equation (show only components that actually react) Ca + (aq) + 2OH  (aq)  Ca(OH) 2 (s) Rb + and Cl  are “spectator” ions.

25

26 Molecular equation, complete ionic equation and net ionic equation Molecular equation

27 Molecular equation, complete ionic equation and net ionic equation

Write the Molecular, Complete Ionic, and Net ionic equations 1. Predict the products formed when aqueous solution of aluminum nitrate is mixed with sodium hydroxide solution. 2. Predict the products formed when a lead(II) nitrate solution is mixed with a sodium iodide solution 28

29 Problem 1 Predict the precipitate formed when aqueous solution of aluminum nitrate is mixed with sodium hydroxide solution.

30 Answer for Problem 1

31 Answer for Problem 1 Net Ionic Equation

32 Problem 2 Predict the precipitate formed when a lead(II) nitrate solution is mixed with a sodium iodide solution

33 Answer for Problem 2

34 Problem 2 Write the molecular equation, the complete ionic equation, and the net ionic equation when a lead(II) nitrate solution is mixed with a sodium iodide solution.

35 Answer for Problem 2 The molecular equation is The complete ionic equation is

36 Answer for Problem 2 The net ionic equation is

37 Acids

38 Bases

39 Reactions that Form Water: Acids + Bases Acids all contain H + cations and an anion Bases all contain OH - anions and a cation when acids dissociate in water they release H + ions and their anions when bases dissociate in water they release OH - ions and their cations

40 Strong acids and strong bases They are called strong acids. They are called strong bases.

41 Important Points about Strong Acids and Strong Bases Six strong acids  HCl, HBr, HI, HNO 3, H 2 SO 4, HClO 3 A strong acid is a substance that completely dissociates (ionizes) in water. (Each molecule breaks up into an H + ion plus an anion. Strong bases  metal hydroxides  NaOH and KOH

42 Important Points about Strong Acids and Strong Bases In the reaction of a strong acid and a strong base, one product is always water and the other is always an ionic compound called a salt, which remains dissolved in the water. This salt can be obtained as a solid by evaporating the water.

43 Acid-Base Reactions in the reaction of an acid with a base, the H + from the acid combines with the OH - from the base to make water the cation from the base combines with the anion from the acid to make the salt acid + base  salt + water H 2 SO 4 (aq) + Ca(OH) 2 (aq)  CaSO 4 (aq) + 2 H 2 O(l) the net ionic equation for an Acid-Base reaction is always H + (aq) + OH - (aq)  H 2 O(l)

44 Example of acid-base reaction

End of Chapter 7 45

46 Reactions of Metals with Nonmetals (Oxidation-Reduction) The metal loses electrons and becomes a cation –We call this process oxidation The nonmetal gains electrons and becomes an anion –We call this process reduction In the reaction, electrons are transferred from the metal to the nonmetal

47 Oxidation-Reduction Reactions All reactions that involve a transfer of one or more electrons are called oxidation- reduction reactions We say that the substance that loses electrons in the reaction is oxidized and the substance that gains electrons in the reaction is reduced.

48 Predicting Products of Metal + Nonmetal Reactions metal + nonmetal  ionic compound –ionic compounds always solids unless dissolved in water in the ionic compound the metal is now a cation in the ionic compound the nonmetal is now an anion to predict direct synthesis of metal + nonmetal ¬determine the charges on the cation and anion from their position on the Periodic Table ­determine numbers of cations and anions needed to have charges cancel ®balance the equation

49 Oxidation-Reduction Reactions (electron transfer reactions) 2Mg (s) + O 2 (g) 2MgO (s) 2Mg 2Mg e - O 2 + 4e - 2O 2- Oxidation half-reaction (lose e - ) Reduction half-reaction (gain e - ) 2Mg + O 2 + 4e - 2Mg O e - 2Mg + O 2 2MgO

50 QUESTION

51 ANSWER

52 ANSWER (continued)

53 Another Kind of Oxidation-Reduction Reaction Some reactions between two non-metals are also oxidation-reduction reaction Any reaction in which O 2 is a reactant or a product will be an oxidation-reduction reaction CH 4 (g) + 2 O 2 (g)  CO 2 (g) + 2 H 2 O(g) 2 SO 3 (g)  2 SO 2 (g) + O 2 (g)

54 Ways to Classify Reactions Reactions that involve solid formation are called precipitation reactions Reactions that involve water formation are called acid-base reactions Both precipitation reactions and acid-base reactions involve compounds exchanging ions, ion exchange reactions are called double displacement reactions

55 Double Displacement Reactions two ionic compounds exchange ions X  Y  (aq) + A  B  (aq)  XB + AY reaction will not occur unless one of the products either (1) precipitates, (2) or is water

56 Ways to Classify Reactions Reactions that involve electron transfer are called oxidation-reduction reactions –Metals + Nonmetal –O 2 as a reactant or product Reactions that occur in aqueous solution because one of the products is a gas are called gas forming reactions NaHCO 3 (aq) + HCl(aq)  NaCl(aq) + CO 2 (g) + H 2 O(l)

57 Ways to Classify Reactions Reactions that involve one ion being transferred from one cation to another are called single replacement reaction X  Y  + A   X + A  Y  Zn(s) + 2 HCl(aq)  ZnCl 2 (aq) + H 2 (g) Fe 2 O 3 (s) + 2 Al(s)  2 Fe(s) + Al 2 O 3 (s)

58 QUESTION

59 ANSWER

60 ANSWER (continued)

61 Other Ways to Classify Reactions Reactions in which O 2 (g) is reacted with a carbon compound are called Combustion Reactions Combustion reactions release a lot of energy Combustion reactions are a subclass of Oxidation- Reduction reactions Combustion of carbon compounds produces CO 2 (g) Combustion of compounds that contain hydrogen produces H 2 O(g) C 3 H 8 (g) + 5 O 2 (g)  3 CO 2 (g) + 4 H 2 O(g)

62 Other Ways to Classify Reactions Reactions in which chemicals combine to make one product are called Synthesis Reactions Metal + Nonmetal reactions can be classified as Synthesis Reactions 2 Na(s) + Cl 2 (g)  2 NaCl(s) Reactions of Metals or Nonmetals with O 2 can be classified as Synthesis Reactions N 2 (g) + O 2 (g)  2 NO(g) These two types of Synthesis Reactions are also subclasses of Oxidation-Reduction Reactions

63 Other Ways to Classify Reactions Reactions in which one reactant breaks down into smaller molecules are called Decomposition Reactions Generally initiated by addition of energy –Addition of electric current or heat Opposite of a Synthesis Reaction 2 NaCl(l)  2 Na(l) + Cl 2 (g) electric current

64 QUESTION

65 ANSWER

66 ANSWER (continued)

67 QUESTION

68 QUESTION (continued)

69 ANSWER

70 QUESTION

71 ANSWER

72 ANSWER (continued)

73 QUESTION

74 ANSWER

75 QUESTION

76 ANSWER

77 ANSWER (continued)

78 ANSWER (continued)