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Chapter 4

Chapter 4. Reactions in Aqueous Solution. 7.1 Predicting Whether a Reaction Will Occur?. Driving Forces Formation of solid Formation of water Transfer of electrons Formation of a gas. 7.2 Reactions in Which a Solid Forms?. Driving forces Precipitation – formation of solid

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Chapter 4

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  1. Chapter 4 Reactions in Aqueous Solution

  2. 7.1 Predicting Whether a Reaction Will Occur? • Driving Forces • Formation of solid • Formation of water • Transfer of electrons • Formation of a gas

  3. 7.2 Reactions in Which a Solid Forms? • Driving forces • Precipitation – formation of solid Ba(NO3)2(aq) + K2CrO4(aq)  BaCrO4(s) + 2KNO3(aq) yellow sol. Colorless Yellow ppt

  4. 7.2 Reactions in Which a Solid Forms? • Acid-Base Neutralization Reactions: Processes in which an acid reacts with a base to yield water plus a salt. HCl(aq) + NaOH(aq)  H2O(l) + NaCl(aq)

  5. Some Ways That Chemical Reactions Occur • Oxidation-Reduction (Redox) Reactions: Processes in which one or more electrons are transferred between reactions partner (atoms, molecules or ions) Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)

  6. Electrolytes in Aqueous Solution • Electrolytes: substances which dissolve in water to produce conducting solution of ions H2O NaCl(s)  Na+(aq) + Cl-(aq) A solution of NaCl conducts electricity because of the movement of charged particles (ions).

  7. Electrolytes in Aqueous Solution • Nonelectrolytes: substances which do not produce ions in aqueous solution H2O C12H22O11(s)  C12H22O11(aq) A solution of C12H22O11 does not conduct electricity because it contains no charged particles (ions).

  8. Electrolytes in Aqueous Solution • Strong electrolytes: compounds that dissociate to a large extent into ions when dissolve in water HCl(aq)  H+(aq) + Cl-(aq)  completely dissociate

  9. CH3CO2H(aq) H1+(aq) + CH3CO21-(aq) Electrolytes in Aqueous Solution Weak electrolytes: compounds that dissociate to a small extent into ions when dissolve in water

  10. Electrolytes in Aqueous Solution Strong Acids: hydrochloric acid, hydrobromic acid, hydroiodic acid, perchloric acid, nitric acid, sulfuric acid.

  11. Predicting product • Ba(NO3)2(aq) + K2CrO4(aq)  yellow solid

  12. Write out all possible formula that can be formed How to Decide What Products Form

  13. Solubility of inorganic compounds at 25C

  14. Examples • Using solubility rules to predict the product of Reactions • KNO3(aq) + BaCl2(g)  • Na2S(aq) + Cu(NO3)2(aq)  • KOH(aq) + Fe(NO3)2(aq) 

  15. Identifying Precipitates in Reactions Where a Solid Forms • Step 1: Write the reactants as they actually exist before any reaction occurs • Step 2: Consider the various solids that could form. • Step 3: use solubility rules to decide whether a solid forms E.g AgNO3(aq) + KCl(aq)  white solid

  16. Describing Reactions in Aqueous Solutions • Molecular equation: shows overall reaction but not necessary the actual forms of the reactants and products in solution AgNO3(aq) + NaCl(aq)  NaNO3(aq) + AgCl(s)

  17. Describing Reactions in Aqueous Solutions • Complete ionic equation: represents all reactants and products that are strong electrolytes as ions. All reactants and products are included. Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq)  Na+(aq) + NO3-(aq) + AgCl(s)

  18. Describing Reactions in Aqueous Solutions • The net ionic equation includes only those components that undergoes a change. Spectator ions are not included Ag+(aq) + Cl-(aq)  AgCl(s) Physical state must be included for all equations or No Credit.

  19. Examples • For each of the following reactions, write molecular equation, the complete ionic equation and the net ionic equation • Cu(NO3)2(aq) + Na2CO3(aq)  • NH4NO3(aq) + KCl(aq) 

  20. 7.4 Reactions That Form Water: Acids and Bases • Arrhenius acids: a substance that produces H+ ions (protons) when it dissolved in water • Strong acids: strong electrolytes • Common strong acids: HCl, HBr, HI, H2SO4, HClO4, HNO3

  21. Arrhenius Acid Dissolve in water HA(aq)  H+(aq) + A-(aq) HCl(aq) + H2O  H3O+(aq) + Cl-(aq)

  22. 7.4 Reactions That Form Water: Acids and Bases • Arrhenius Bases: substance that produces –OH ion (hydroxide ions) in water • Strong bases: Strong electrolytes • Common strong bases: KOH, LiOH, NaOH, Ba(OH)2 and Sr(OH)2 MOH(aq)  M+(aq) + -OH(aq)

  23. 7.4 Reactions That Form Water: Acids and Bases dissolved in H2O NaOH(aq) ----------------- Na+(aq) + -OH(aq) Weak Base NH3(aq) + H2O(l)  NH4+(aq) + -OH(aq)

  24. Acids, Bases, and Neutralization Reactions Strong acids and strong bases are strong electrolytes. Weak acids and weak bases are weak electrolytes.

  25. HA + MOH HA + MOH MA + H2O MA + HOH Acids, Bases, and Neutralization Reactions • These acid-base neutralization reactions are double replacement reactions just like precipition or Acid Base Salt Water

  26. Writing Equations for Acid-Base Reactions • HNO3(aq) + Sr(OH)2(aq)  • H2SO4(aq) + NaOH(aq) 

  27. 2Fe2O3(s) + 3C(s) 4Fe(s) + 3O2(g) 2Fe2O3(s) 4Fe(s) + 3CO2(g) Oxidation-Reduction (Redox) Reactions Rusting of iron: an oxidation of Fe Manufacture of iron: a reduction of Fe

  28. Oxidation-Reduction (Redox) Reactions • Oxidation Number (state): a value which indicates whether an atom is neutral, electron-rich, or electron-poor

  29. Rules for Assigning Oxidation Numbers • An atom in its elemental state has an oxidation number of 0 Na H2 Br2 S Ne Oxidation number 0

  30. Rules for Assigning Oxidation Numbers • A monatomic ion has an oxidation number identical to its charge Na1+ +1 Ca2+ +2 Al3+ +3 Cl1- -1 O2- -2

  31. 1- H O H Ca H Rules for Assigning Oxidation Numbers • An atom in a polyatomic ion or in a molecular compound usually has the same oxidation number it would have if it were a monatomic ion. • Hydrogen can be either +1 or -1. -1 +2 -1 +1 -2

  32. H O H Rules for Assigning Oxidation Numbers • Oxygen usually has an oxidation number of -2. H O O H +1 -2 +1 +1 -1 -1 +1

  33. Cl O Cl Rules for Assigning Oxidation Numbers • Halogens usually have an oxidation number of -1 except when bonding to oxygen. H Cl +1 -1 +1 -2 +1

  34. Rules for Assigning Oxidation Numbers • The sum of the oxidation numbers is 0 for a neutral compound and is equal to the net charge for a polyatomic ion. H2SO3 2(+1) + x + 3(-2) = 0 (net charge) x = +4 x -2 Cr2O72- 2(x) + 7(-2) = -2 (net charge) x = +6 x -2

  35. Examples • Determine the oxidation for each atom in the following compounds • CdS • AlH3 • NH4+ • Na2Cr2O7

  36. Redox Reaction • Oxidizing Agent • Causes reduction • Loses one or more electrons • Undergoes oxidation • Oxidation number of atom increases • Reduction: Gaining e- (RIG) • Reducing Agent • Causes oxidation • Gains one or more electrons • Undergoes reduction • Oxidation number of atom decreases • Oxidation: Losing e- (OIL)

  37. reduction 0 -2 4Fe(s) + 3O2(g) 2Fe2 O3 (s) 0 +3 oxidation Identifying Redox Reactions Oxidizing Agent Reducing Agent

  38. Identifying Redox Reactions Oxidizing Agent reduction +3 0 2Fe2O3 (s) + 3 C (s) 4Fe(s) + 3 C O2 (g) 0 +4 Reducing Agent oxidation

  39. Redox Half Reaction • Fe(s) + Cu 2+ (aq)  Fe 2+ (aq) + Cu(s) Oxidation: Fe(s)  Fe 2+ (aq) + 2e- Reduction: Cu 2+ (aq) + 2e-  Cu(s)

  40. Examples • For each of the following reactions, show how electrons are gained and lost • 2 Al(s) + 3 I2(g)  2 AlI3(s) • 2 Cs(s) + F2(g)  2 CsF(s) • 2SO2(g) + O2(g)  2SO3(g)

  41. 2Ag(s) + Cu2+(g) Cu(s) + 2Ag1+(g) 2Ag1+(aq) + Cu(s) Cu2+(aq) + 2Ag(s) The Activity Series of the Elements Which one of these reactions will occur?

  42. The Activity Series of the Elements The elements that are higher up in the table are more likely to be oxidized. Thus, any element higher in the activity series will reduce the ion of any element lower in the activity series.

  43. 2Ag(s) + Cu2+(g) Cu(s) + 2Ag1+(g) 2Ag1+(aq) + Cu(s) Cu2+(aq) + 2Ag(s) The Activity Series of the Elements Which one of these reactions will occur?

  44. Examples • Mn(s) + AuCl3(aq)  • Fe(s) + Zn(NO3)2(aq)  • Cu(s) + HCl(aq) 

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