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Dr. Subhash C. Goel South GA College Douglas, GA

Lecture Presentation. Dr. Subhash C. Goel South GA College Douglas, GA. © 20 12 Pearson Education, Inc. Solutions. Solutions are defined as homogeneous mixtures of two or more pure substances. The solvent is present in greatest abundance. All other substances are solutes.

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Dr. Subhash C. Goel South GA College Douglas, GA

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  1. Lecture Presentation Dr. Subhash C. Goel South GA College Douglas, GA © 2012 Pearson Education, Inc.

  2. Solutions • Solutions are defined as homogeneous mixtures of two or more pure substances. • The solvent is present in greatest abundance. • All other substances are solutes. © 2012 Pearson Education, Inc.

  3. In aqueous solutions (aq) *solvent is water *solute can be ionic compounds, aqueous acids, bases, or molecular compounds • Water is one of the most common solvent • It’s a polar molecule O- a hydrogen bond H + H +

  4. “Like dissolves like” A solvent such as water is needed to dissolve polar solutes such as sugar and ionic solutes such as NaCl. A solvent such as hexane (C6H14) is needed to dissolve nonpolar solutes such as oil or grease.

  5. Learning Check Which of the following solutes will dissolve in water? Why? 1) Na2SO4 2) gasoline 3) I2 4) HCl

  6. Solution Which of the following solutes will dissolve in water? Why? 1) Na2SO4 Yes, polar (ionic) 2) gasoline No, nonpolar 3) I2 No, nonpolar 4) HCl Yes, polar

  7. 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. © 2012 Pearson Education, Inc.

  8. Dissociation • An electrolyte is a substances that dissociates into ions when dissolved in water. © 2012 Pearson Education, Inc.

  9. Solutions • Anonelectrolyte may dissolve in water, but it does not dissociate into ions when it does so. © 2012 Pearson Education, Inc.

  10. Electrolytes and Nonelectrolytes Soluble ionic compounds tend to be electrolytes. © 2012 Pearson Education, Inc.

  11. Electrolytes and Nonelectrolytes Molecular compounds tend to be nonelectrolytes, except for acids and bases. © 2012 Pearson Education, Inc.

  12. Electrolytes • A strong electrolyte dissociates completely when dissolved in water. • A weak electrolyte only dissociates partially when dissolved in water. © 2012 Pearson Education, Inc.

  13. Strong Electrolytes Are… • Strong acids • Strong bases • Soluble ionic salts © 2012 Pearson Education, Inc.

  14. 1. Group IA and ammonium compounds are soluble. • 2. Acetates and nitrates are soluble. • 3. Most chlorides, bromides, and iodides are soluble. • Exceptions: AgCl, Hg2Cl2, PbCl2;AgBr, HgBr2, Hg2Br2, PbBr2;AgI, HgI2, Hg2I2, PbI2 • 4. Most sulfates are soluble. • Exceptions: CaSO4, SrSO4, BaSO4, Ag2SO4, Hg2SO4, PbSO4 Solubility Rules Copyright © Cengage Learning. All rights reserved.

  15. 5. Most carbonates are insoluble. Exceptions: Group IA carbonates and (NH4)2CO3 6. Most phosphates are insoluble. Exceptions: Group IA phosphates and (NH4)3PO4 7. Most sulfides are insoluble. Exceptions: Group IA sulfides and (NH4)2S 8. Most hydroxides are insoluble. Exceptions: Group IA hydroxides, Ca(OH)2, Sr(OH)2, Ba(OH)2 Copyright © Cengage Learning. All rights reserved.

  16. © 2012 Pearson Education, Inc.

  17. Exercise Using Solubility Rules Classify these ionic compounds as soluble or insoluble in water: (a) sodium carbonate, Na2CO3, (b) lead sulfate, PbSO4.

  18. Metathesis comes from a Greek word that means “to transpose.” AgNO3(aq) + KCl(aq) AgCl(s) + KNO3(aq) Metathesis (Exchange) Reactions © 2012 Pearson Education, Inc.

  19. Metathesis comes from a Greek word that means “to transpose.” It appears as though the ions in the reactant compounds exchange, or transpose, ions: AgNO3(aq) + KCl(aq) AgCl(s) + KNO3(aq) Metathesis (Exchange) Reactions © 2012 Pearson Education, Inc.

  20. Exercise Predicting a Metathesis Reaction (a) Predict the identity of the precipitate that forms when aqueous solutions of BaCl2 and K2SO4 are mixed. (b) Write the balanced chemical equation for the reaction.

  21. 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. © 2012 Pearson Education, Inc.

  22. The molecular equation lists the reactants and products in their molecular form: AgNO3(aq) + KCl(aq) AgCl(s) + KNO3(aq) Molecular Equation © 2012 Pearson Education, Inc.

  23. 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: Ag+(aq) + NO3−(aq) + K+(aq) + Cl−(aq) AgCl(s) + K+(aq) + NO3−(aq) Ionic Equation © 2012 Pearson Education, Inc.

  24. 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) + NO3−(aq) + K+(aq) + Cl−(aq) AgCl(s) + K+(aq) + NO3−(aq) Net Ionic Equation © 2012 Pearson Education, Inc.

  25. 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) Net Ionic Equation © 2012 Pearson Education, Inc.

  26. 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) + NO3−(aq) + K+(aq) + Cl−(aq) AgCl(s) + K+(aq) + NO3−(aq) Net Ionic Equation © 2012 Pearson Education, Inc.

  27. Writing Net Ionic Equations • Write a balanced molecular equation. • Dissociate all strong electrolytes. • Cross out anything that remains unchanged from the left side to the right side of the equation. • Write the net ionic equation with the species that remain. © 2012 Pearson Education, Inc.

  28. Decide whether the following reaction occurs. If it does, write the molecular, ionic, and net ionic equations. KBr + MgSO4 • Determine the product formulas: • K+ and SO42− make K2SO4 • Mg2+and Br − make MgBr2 • Determine whether the products are soluble: • K2SO4 is soluble • MgBr2 is soluble • KBr + MgSO4 no reaction Copyright © Cengage Learning. All rights reserved.

  29. Decide whether the following reaction occurs. If it does, write the molecular, ionic, and net ionic equations. NaOH + MgCl2 • Determine the product formulas: • Na+ and Cl− make NaCl • Mg2+and OH− make Mg(OH)2 • Determine whether the products are soluble: • NaCl is soluble • Mg(OH)2 is insoluble Copyright © Cengage Learning. All rights reserved.

  30. Molecular Equation (Balance the reaction and include state symbols) 2NaOH(aq) + MgCl2(aq)  2NaCl(aq) + Mg(OH)2(s) Ionic Equation 2Na+(aq) + 2OH−(aq) + Mg2+(aq) + 2Cl−(aq)  2Na+(aq) + 2Cl−(aq) + Mg(OH)2(s) Net Ionic Equation 2OH−(aq) + Mg2+(aq)  Mg(OH)2(s) Copyright © Cengage Learning. All rights reserved.

  31. Decide whether the following reaction occurs. If it does, write the molecular, ionic, and net ionic equations. K3PO4 + CaCl2 • Determine the product formulas: • K+ and Cl− make KCl • Ca2+and PO43− make Ca3(PO4)2 • Determine whether the products are soluble: • KCl is soluble • Ca3(PO4)2 is insoluble Copyright © Cengage Learning. All rights reserved.

  32. Molecular Equation (Balance the reaction and include state symbols) 2K3PO4(aq) + 3CaCl2(aq)  6KCl(aq) + Ca3(PO4)2(s) Ionic Equation 6K+(aq) + 2PO43−(aq) + 3Ca2+(aq) + 6Cl−(aq)  6K+(aq) + 6Cl−(aq) + Ca3(PO4)2(s) Net Ionic Equation 2PO43−(aq) + 3Ca2+(aq)  Ca3(PO4)2(s) Copyright © Cengage Learning. All rights reserved.

  33. Types of Chemical Reactions • Precipitation reactions: a solid ionic substance forms from the mixture of two solutions of ionic substances. • Acid–base reactions: reactions that involve the transfer of a proton (H+) between reactants. • Oxidation–reductionreactions: reactions that involve the transfer of electrons between reactants. Copyright © Cengage Learning. All rights reserved.

  34. A precipitate is an insoluble solid compound formed during a chemical reaction in solution. Predicting Precipitation Reactions 1. Predict the products (exchange of parts). 2. Determine the state of each product: (s), (l), (g), (aq). 3. If all products are aqueous (aq), no net reaction occurred. Copyright © Cengage Learning. All rights reserved.

  35. Arrhenius Acid A substance that produces hydrogen ions, H+, when it dissolves in water. Arrhenius Base A substance that produces hydroxide ions, OH−, when it dissolves in water. Copyright © Cengage Learning. All rights reserved.

  36. Brønsted–Lowry Acid The species (molecule or ion) that donates a proton to another species in a proton−transfer reaction. Brønsted–Lowry Base The species (molecule or ion) that accepts a proton from another species in a proton−transfer reaction. Copyright © Cengage Learning. All rights reserved.

  37. Strong Acid An acid that ionizes completely in water. It is present entirely as ions; it is a strong electrolyte. Common strong acids: HNO3H2SO4HClO4 HCl HBr HI Copyright © Cengage Learning. All rights reserved.

  38. Weak Acid An acid that only partly ionizes in water. It is present primarily as molecules and partly as ions; it is a weak electrolyte. If an acid is not strong, it is weak. Copyright © Cengage Learning. All rights reserved.

  39. In Figure A, a solution of HCl (a strong acid) illustrated on a molecular/ionic level, shows the acid as all ions. In Figure B, a solution of HF (a weak acid) also illustrated on a molecular/ionic level, shows mostly molecules with very few ions. Copyright © Cengage Learning. All rights reserved.

  40. Strong Base A base that ionizes completely in water. It is present entirely as ions; it is a strong electrolyte. Common strong bases: LiOH NaOH KOH Ca(OH)2 Sr(OH)2 Ba(OH)2 Copyright © Cengage Learning. All rights reserved.

  41. Weak Base A base that is only partly ionized in water. It is present primarily as molecules and partly as ions; it is a weak electrolyte. These are often nitrogen bases such as NH3: NH3(aq) + H2O(l)  NH4+(aq) + OH−(aq) If a base is not strong, it is weak. Copyright © Cengage Learning. All rights reserved.

  42. Classify the following as strong or weak acids or bases: a. KOH b. H2S c. CH3NH2 d. HClO4 a. KOH is a strong base. b. H2S is a weak acid. c. CH3NH2 is a weak base. d. HClO4 is a strong acid. Copyright © Cengage Learning. All rights reserved.

  43. Neutralization Reaction A reaction of an acid and a base that results in an ionic compound (a salt) and possibly water. Copyright © Cengage Learning. All rights reserved.

  44. Write the molecular, ionic, and net ionic equations for the neutralization of sulfurous acid, H2SO3, by potassium hydroxide, KOH. Copyright © Cengage Learning. All rights reserved.

  45. Molecular Equation (Balance the reaction and include state symbols) H2SO3(aq) + 2KOH(aq)  2H2O(l) + K2SO3(aq) Ionic Equation H2SO3(aq) + 2K+(aq) + 2OH−(aq)  2H2O(l) + 2K+(aq) + SO32−(aq) Net Ionic Equation H2SO3(aq) + 2OH−(aq) 2H2O(l) + SO32−(aq) Copyright © Cengage Learning. All rights reserved.

  46. Acid−base reactions with gas−formation Sulfides, carbonates, sulfites react with acid to form a gas. Na2S(aq) + 2HCl(aq)  2NaCl(aq) + H2S(g) Na2CO3(aq) + 2HCl(aq)  2NaCl(aq) + H2O(l) + CO2(g) Na2SO3(aq) + 2HCl(aq)  2NaCl(aq) + H2O(l) + SO2(g) Copyright © Cengage Learning. All rights reserved.

  47. Write the molecular, ionic, and net ionic equations for the reaction of copper(II) carbonate with hydrochloric acid. Copyright © Cengage Learning. All rights reserved.

  48. Molecular Equation (Balance the reaction and include state symbols) CuCO3(s) + 2HCl(aq)  CuCl2(aq) + H2O(l) + CO2(g) Ionic Equation CuCO3(s) + 2H+(aq) + 2Cl−(aq)  Cu2+(aq) + 2Cl−(aq) + H2O(l) + CO2(g) Net Ionic Equation CuCO3(s) + 2H+(aq) Cu2+(aq) + H2O(l) + CO2(g) Copyright © Cengage Learning. All rights reserved.

  49. Oxidation-Reduction Reactions • An oxidation occurs when an atom or ion loses electrons. • A reduction occurs when an atom or ion gains electrons. • One cannot occur without the other. © 2012 Pearson Education, Inc.

  50. 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. © 2012 Pearson Education, Inc.

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