1. Reactions in Aqueous Solutions Chapter 7

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

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 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 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. Figure 7.1: The precipitation reaction that occurs when yellow potassium chromate, K 2 CrO 4 (aq), is mixed with a colorless barium nitrate solution, Ba(NO 3 ) 2 (aq)

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

6. Figure 7.2: Electrical conductivity of aqueous solutions

7. Dissociation potassium chloride dissociates in water into potassium cations and chloride anions 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 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

8. Dissociation potassium sulfate dissociates in water into potassium cations and sulfate anions 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

9. Predicting the Products of a Precipitation Reaction 1. Determine what ions each aqueous reactant has 2.Exchange Ions (+) ion from one reactant with (-) ion from other (+) ion from one reactant with (-) ion from other 3.Balance Charges of combined ions to get formula of each product 4.Balance the Equation count atoms count atoms 5.Determine Solubility of Each Product in Water solubility rules solubility rules if product is insoluble or slightly soluble, it will precipitate if product is insoluble or slightly soluble, it will precipitate Pb(NO 3 ) 2 (aq) + CaCl 2 (aq) ---->

10. Solubility Rules 1.Most compounds that contain NO 3 - ions are soluble 2.Most compounds that contain Na +, K +, or NH 4 + ions are soluble 3.Most compounds that contain Cl - ions are soluble, except AgCl, PbCl 2, and Hg 2 Cl 2 4.Most compounds that contain SO 4 2- ions are soluble, except BaSO 4, PbSO 4, CaSO 4 5.Most compounds that contain OH - ions are slightly soluble (will precipitate), except NaOH, KOH, are soluble and Ba(OH) 2, Ca(OH) 2 are moderately soluble 6.Most compounds that contain S 2-, CO 3 2-, or PO 4 3- ions are slightly soluble (will precipitate)

11. Figure 7.3: Solubilities of common compounds

12. Figure 7.4: Precipitation of silver chloride

13. Ionic Equations equations which describe the chemicals put into the water and the product molecules are called molecular equations equations which describe the chemicals put into the water and the product molecules are called molecular equations KCl(aq) + AgNO 3 (aq)  KNO 3 (aq) + AgCl(s) equations which describe the actual ions and molecules in the solutions as well as the molecules of solid, liquid and gas not dissolved are called ionic equations equations which describe the actual ions and molecules in the solutions as well as the molecules of solid, liquid and gas not dissolved are called ionic equations K + (aq) + Cl - (aq) + Ag + (aq) + NO 3 - (aq)  K + (aq) + NO 3 - (aq) + AgCl (s)

14. Ionic Equations ions that are both reactants and products are called spectator ions 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 an ionic equation in which the spectator ions are dropped is called a net ionic equation Cl - (aq) + Ag + (aq)  AgCl (s) Cl - (aq) + Ag + (aq)  AgCl (s)

15. Electrolytes electrolytes are substances whose aqueous solution is a conductor of electricity electrolytes are substances whose aqueous solution is a conductor of electricity all electrolytes have ions dissolved in water all electrolytes have ions dissolved in water in strong electrolytes, virtually all the molecules are dissociated into ions in strong electrolytes, virtually all the molecules are dissociated into ions in nonelectrolytes, none of the molecules are dissociated into ions in nonelectrolytes, none of the molecules are dissociated into ions in weak electrolytes, a small percentage of the molecules are dissociated into ions in weak electrolytes, a small percentage of the molecules are dissociated into ions

16. Figure 7.5: When gaseous HCl is dissolved in water, each molecule dissociates to produce H + and Cl - ions

17. Reactions that Form Water: Acids + Bases Acids all contain H + cations and an anion Acids all contain H + cations and an anion HCl, HBr, HI, HNO 3, H 2 SO 4 HCl, HBr, HI, HNO 3, H 2 SO 4 Bases all contain OH - anions and a cation Bases all contain OH - anions and a cation NaOH, KOH, NH 4 OH NaOH, KOH, NH 4 OH when acids dissociate in water they release H + ions and their anions when acids dissociate in water they release H + ions and their anions when bases dissociate in water they release OH - ions and their cations when bases dissociate in water they release OH - ions and their cations

18. Acid-Base Reactions in the reaction of an acid with a base, the H +1 from the acid combines with the OH -1 from the base to make water in the reaction of an acid with a base, the H +1 from the acid combines with the OH -1 from the base to make water the cation from the base combines with the anion from the acid to make the salt 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 the net ionic equation for an Acid-Base reaction is always 2 H + (aq) + 2 OH - (aq)  2H 2 O(l)

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

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

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

22. Oxidation-Reduction Examples 2 Na (s) + Cl 2 (g) ----> 2 NaCl (s) 2 Na (s) + Cl 2 (g) ----> 2 NaCl (s) 2 Mg (s) + O 2 (g) ----> 2 MgO (s) 2 Mg (s) + O 2 (g) ----> 2 MgO (s) 2 Al (s) + Fe 2 O 3 (s) ----> 2 Fe (s) + Al 2 O 3 (s) 2 Al (s) + Fe 2 O 3 (s) ----> 2 Fe (s) + Al 2 O 3 (s) 2 Al (s) + 3 I 2 (s) ----> 2 AlI 3 (s) 2 Al (s) + 3 I 2 (s) ----> 2 AlI 3 (s)

23. Another Kind of Oxidation-Reduction Reaction Another Kind of Oxidation-Reduction Reaction Some reactions between two non-metals are also 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 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)

24. Figure 7.8: For launch, the space shuttle orbiter is attached to two solid-fuel rockets and a fuel tank that supplies hydrogen and oxygen to the orbiter’s engines 2 H 2 (g) + O 2 (g) ----> 2 H 2 O (g) + ENERGY

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

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

27. Ways to Classify Reactions Reactions that involve electron transfer are called oxidation-reduction reactions Reactions that involve electron transfer are called oxidation-reduction reactions Metals + Nonmetal Metals + Nonmetal O 2 as a reactant or product 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 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)

28. Ways to Classify Reactions Reactions that involve one ion being transferred from one cation to another are called single replacement reaction 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)

29. Other Ways to Classify Reactions Reactions in which O 2 (g) is reacted with a carbon compound are called Combustion 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 release a lot of energy Combustion reactions are a subclass of Oxidation-Reduction reactions Combustion reactions are a subclass of Oxidation-Reduction reactions Combustion of carbon compounds produces CO 2 (g) Combustion of carbon compounds produces CO 2 (g) Combustion of compounds that contain hydrogen produces H 2 O(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)

30. Other Ways to Classify Reactions Reactions in which chemicals combine to make one product are called Synthesis Reactions Reactions in which chemicals combine to make one product are called Synthesis Reactions Metal + Nonmetal reactions can be classified as 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 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 These two types of Synthesis Reactions are also subclasses of Oxidation-Reduction Reactions

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

32. Figure 7.11: Classes of reactions

33. Figure 7.12: Summary of classes of reactions