logging in or signing up types of chemical reactions and solution abbas1410 Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 2776 Category: Education License: All Rights Reserved Like it (0) Dislike it (2) Added: November 08, 2008 This Presentation is Public Favorites: 0 Presentation Description No description available. Comments Posting comment... Premium member Presentation Transcript Chapter 4Type of Chemical Reactions and Solution Stoichiometric : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Chapter 4Type of Chemical Reactions and Solution Stoichiometric Water, Nature of aqueous solutions, types of electrolytes, dilution. Types of chemical reactions: precipitation, acid-base and oxidation reactions. Stoichiometry of reactions and balancing the chemical equations. Aqueous Solutions : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Aqueous Solutions Water is the dissolving medium, or solvent. Slide 3: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 Figure 4.1: (Left) The water molecule is polar. (Right) A space-filling model of the water molecule. Slide 4: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Figure 4.2: Polar water molecules interact with the positive and negative ions of a salt assisting in the dissolving process. Cl- Na+ Cl- Na+ H2O Some Properties of Water : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Some Properties of Water Water is “bent” or V-shaped. The O-H bonds are covalent. Water is a polar molecule. Hydration occurs when salts dissolve in water. Slide 6: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 Figure 4.3: (a) The ethanol molecule contains a polar O—H bond similar to those in the water molecule. (b) The polar water molecule interacts strongly with the polar O—H bond in ethanol. This is a case of "like dissolving like." A Solute : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 A Solute dissolves in water (or other “solvent”) changes phase (if different from the solvent) is present in lesser amount (if the same phase as the solvent) A Solvent : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 A Solvent retains its phase (if different from the solute) is present in greater amount (if the same phase as the solute) General Rule for dissolution : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 General Rule for dissolution Like dissolve like Polar dissolve polar (water dissolve ethanol) Non-polar dissolve nonpolar (benzene dissolve fat) Slide 10: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Figure 4.5: When solid NaCl dissolves, the Na+ and Cl- ions are randomly dispersed in the water. Electrolytes : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Electrolytes Strong - conduct current efficiently NaCl, HNO3 Weak - conduct only a small current vinegar, tap water Non - no current flows pure water, sugar solution Slide 12: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Figure 4.4: Electrical conductivity of aqueous solutions. Acids : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Acids Strong acids - dissociate completely to produce H+ in solution hydrochloric and sulfuric acid HCl , H2SO4 Weak acids - dissociate to a slight extent to give H+ in solution acetic and formic acid CH3COOH, CH2O Bases : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Bases Strong bases - react completely with water to give OH ions. sodium hydroxide Weak bases - react only slightly with water to give OH ions. ammonia Slide 15: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Figure 4.6: HCl(aq) is completely ionized. Slide 16: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 Figure 4.7: An aqueous solution of sodium hydroxide. Slide 17: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 Figure 4.8: Acetic acid (HC2H3O2) exists in water mostly as undissociated molecules. Only a small percentage of the molecules are ionized. Molarity : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 Molarity Molarity (M) = moles of solute per volume of solution in liters: Common Terms of Solution Concentration : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 Common Terms of Solution Concentration Stock - routinely used solutions prepared in concentrated form. Concentrated - relatively large ratio of solute to solvent. (5.0 M NaCl) Dilute - relatively small ratio of solute to solvent. (0.01 M NaCl): (MV)initial=(MV)Final Slide 20: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20 Figure 4.10: Steps involved in the preparation of a standard aqueous solution. Slide 21: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 Figure 4.12: Dilution Procedure (a) A measuring pipet is used to transfer 28.7mL of 17.4 M acetic acid solution to a volumetric flask. (b) Water is added to the flask to the calibration mark. (c) The resulting solution is 1.00 M acetic acid. Types of Solution Reactions : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 Types of Solution Reactions Precipitation reactions AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq) Acid-base reactions NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l) Oxidation-reduction reactions Fe2O3(s) + Al(s) Fe(l) + Al2O3(s) Simple Rules for Solubility : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23 Simple Rules for Solubility 1. Most nitrate (NO3) salts are soluble. 2. Most alkali (group 1A) salts and NH4+ are soluble. 3. Most Cl, Br, and I salts are soluble (NOT Ag+, Pb2+, Hg22+) 4. Most sulfate salts are soluble (NOT BaSO4, PbSO4, HgSO4, CaSO4) 5. Most OH salts are only slightly soluble (NaOH, KOH are soluble, Ba(OH)2, Ca(OH)2 are marginally soluble) 6. Most S2, CO32, CrO42, PO43 salts are only slightly soluble. Slide 24: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 24 Figure 4.13: When yellow aqueous potassium chromate is added to a colorless barium nitrate solution, yellow barium chromate precipitates. Describing Reactions in SolutionPrecipitation : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 25 Describing Reactions in SolutionPrecipitation 1. Molecular equation (reactants and products as compounds) AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq) 2. Complete ionic equation (all strong electrolytes shown as ions) Ag+(aq) + NO3 (aq) + Na+ (aq) + Cl(aq) AgCl(s) + Na+ (aq) + NO3 (aq) Describing Reactions in Solution (continued) : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 26 Describing Reactions in Solution (continued) 3. Net ionic equation (show only components that actually reacts) Ag+(aq) + Cl(aq) AgCl(s) Na+ and NO3 are spectator ions. Slide 27: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 27 Acid-Base Reactions An acid produces H+ ions in water A base produces OH- ions in water An acid is a proton donor A base is a proton acceptor Arrhenius’s concept Bronsted & Lowrys’ concept Performing Calculations for Acid-Base Reactions : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 28 Performing Calculations for Acid-Base Reactions 1. List initial species and predict reaction. 2. Write balanced net ionic reaction. 3. Calculate moles of reactants. 4. Determine limiting reactant. 5. Calculate moles of required reactant/product. 6. Convert to grams or volume, as required. Remember: n H+ = n OH- (MV) H+ = (MV) OH- Neutralization Reaction : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 29 Neutralization Reaction 4.3 Key Titration Terms : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 30 Key Titration Terms Titrant - solution of known concentration used in titration Analyte - substance being analyzed Equivalence point - enough titrant added to react exactly with the analyte Endpoint - the indicator changes color so you can tell the equivalence point has been reached. movie Oxidation-Reduction Reactions : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 31 Oxidation-Reduction Reactions (electron transfer reactions) Oxidation half-reaction (lose e-) Reduction half-reaction (gain e-) Slide 32: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 32 Redox Reactions : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 33 Redox Reactions Many practical or everyday examples of redox reactions: Corrosion of iron (rust formation) Forest fire Charcoal grill Natural gas burning Batteries Production of Al metal from Al2O3 (alumina) Metabolic processes combustion Rules for Assigning Oxidation States : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 34 Rules for Assigning Oxidation States 1. Oxidation state of an atom in an element = 0 2. Oxidation state of monatomic element = charge 3. Oxygen = 2 in covalent compounds (except in peroxides where it = 1) 4. H = +1 in covalent compounds 5. Fluorine = 1 in compounds 6. Sum of oxidation states = 0 in compounds Sum of oxidation states = charge of the ion Slide 35: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 35 Slide 36: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 36 Zn is oxidized Cu2+ is reduced Zn is the reducing agent Cu2+ is the oxidizing agent 4.4 Ag+ is reduced Ag+ is the oxidizing agent Slide 37: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 37 NaIO3 Na = +1 O = -2 3x(-2) + 1 + ? = 0 I = +5 IF7 F = -1 7x(-1) + ? = 0 I = +7 K2Cr2O7 O = -2 K = +1 7x(-2) + 2x(+1) + 2x(?) = 0 Cr = +6 4.4 Balancing by Half-Reaction Method : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 38 Balancing by Half-Reaction Method 1. Write separate reduction, oxidation reactions. 2. For each half-reaction: Balance elements (except H, O) Balance O using H2O Balance H using H+ Balance charge using electrons Balancing by Half-Reaction Method (continued) : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 39 Balancing by Half-Reaction Method (continued) 3. If necessary, multiply by integer to equalize electron count. 4. Add half-reactions. 5. Check that elements and charges are balanced. Half-Reaction Method - Balancing in Base : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 40 Half-Reaction Method - Balancing in Base 1. Balance as in acid. 2. Add OH that equals H+ ions (both sides!) 3. Form water by combining H+, OH. 4. Check elements and charges for balance. Balancing Redox Equations : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 41 Balancing Redox Equations Example: Balance the following redox reaction: Cr2O72- + Fe2+ Cr3+ + Fe3+ (acidic soln) 1) Break into half reactions: Cr2O72- Cr3+ Fe2+ Fe3+ Slide 42: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 42 Balancing Redox Equations Slide 43: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 43 Balancing Redox Equations 2) Balance each half reaction (cont) Slide 44: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 44 Balancing Redox Reactions 3) Multiply by integer so e- lost = e- gained Slide 45: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 45 Balancing Redox Reactions 3) Multiply by integer so e- lost = e- gained 6 Fe2+ 6 Fe3+ + 6 e- 6 e- + Cr2O72- + 14 H+ 2 Cr3+ + 7 H2O 4) Add both half reactions Cr2O72- + 6 Fe2+ + 14 H+ 2 Cr3+ + 6 Fe3+ + 7 H2O Slide 46: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 46 Balancing Redox Reactions Cr2O72- + 6 Fe2+ + 14 H+ 2 Cr3+ + 6 Fe3+ + 7 H2O 5) Check the equation 2 Cr 2 Cr 7 O 7 O 6 Fe 6 Fe 14 H 14 H +24 + 24 Slide 47: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 47 Balancing Redox Reactions Procedure for Basic Solutions: Divide the equation into 2 incomplete half reactions one for oxidation one for reduction Slide 48: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 48 Balancing Redox Reactions Balance each half-reaction: balance elements except H and O balance O atoms by adding H2O balance H atoms by adding H+ add 1 OH- to both sides for every H+ added combine H+ and OH- on same side to make H2O cancel the same # of H2O from each side balance charge by adding e- to side with greater overall + charge different Slide 49: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 49 Balancing Redox Equations Multiply each half reaction by an integer so that # e- lost = # e- gained Add the half reactions together. Simply where possible by canceling species appearing on both sides of equation Check the equation # of atoms total charge on each side Slide 50: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 50 Balancing Redox Reactions Example: Balance the following redox reaction. NH3 + ClO- Cl2 + N2H4 (basic soln) NH3 N2H4 ClO- Cl2 1) Break into half reactions: Slide 51: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 51 Balancing Redox Reactions 2) Balance each half reaction: + 2 OH- + 2 OH- Slide 52: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 52 Balancing Redox Reactions 2) Balance each half reaction: Slide 53: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 53 Balancing Redox Reactions 3) Multiply by integer so # e- lost = # e- gained 2 NH3 + 2 OH- N2H4 + 2 H2O + 2 e- 2 e- + 2 ClO- + 2 H2O Cl2 + 4 OH- 4) Add both half reactions 2 NH3 + 2 OH- + 2ClO- + 2 H2O N2H4 + 2 H2O + Cl2 + 4 OH- Slide 54: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 54 Balancing Redox Reactions 5) Cancel out common species 2 NH3 + 2 OH- + 2 ClO- + 2 H2O N2H4 + 2 H2O + Cl2 + 4 OH- 2 6) Check final equation: 2 N 2 N 6 H 6 H 2 Cl 2 Cl 2 O 2 O -2 -2 Slide 55: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 55 Slide 56: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 56 You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.
types of chemical reactions and solution abbas1410 Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 2776 Category: Education License: All Rights Reserved Like it (0) Dislike it (2) Added: November 08, 2008 This Presentation is Public Favorites: 0 Presentation Description No description available. Comments Posting comment... Premium member Presentation Transcript Chapter 4Type of Chemical Reactions and Solution Stoichiometric : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Chapter 4Type of Chemical Reactions and Solution Stoichiometric Water, Nature of aqueous solutions, types of electrolytes, dilution. Types of chemical reactions: precipitation, acid-base and oxidation reactions. Stoichiometry of reactions and balancing the chemical equations. Aqueous Solutions : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Aqueous Solutions Water is the dissolving medium, or solvent. Slide 3: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 Figure 4.1: (Left) The water molecule is polar. (Right) A space-filling model of the water molecule. Slide 4: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Figure 4.2: Polar water molecules interact with the positive and negative ions of a salt assisting in the dissolving process. Cl- Na+ Cl- Na+ H2O Some Properties of Water : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Some Properties of Water Water is “bent” or V-shaped. The O-H bonds are covalent. Water is a polar molecule. Hydration occurs when salts dissolve in water. Slide 6: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 Figure 4.3: (a) The ethanol molecule contains a polar O—H bond similar to those in the water molecule. (b) The polar water molecule interacts strongly with the polar O—H bond in ethanol. This is a case of "like dissolving like." A Solute : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 A Solute dissolves in water (or other “solvent”) changes phase (if different from the solvent) is present in lesser amount (if the same phase as the solvent) A Solvent : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 A Solvent retains its phase (if different from the solute) is present in greater amount (if the same phase as the solute) General Rule for dissolution : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 General Rule for dissolution Like dissolve like Polar dissolve polar (water dissolve ethanol) Non-polar dissolve nonpolar (benzene dissolve fat) Slide 10: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Figure 4.5: When solid NaCl dissolves, the Na+ and Cl- ions are randomly dispersed in the water. Electrolytes : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Electrolytes Strong - conduct current efficiently NaCl, HNO3 Weak - conduct only a small current vinegar, tap water Non - no current flows pure water, sugar solution Slide 12: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Figure 4.4: Electrical conductivity of aqueous solutions. Acids : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Acids Strong acids - dissociate completely to produce H+ in solution hydrochloric and sulfuric acid HCl , H2SO4 Weak acids - dissociate to a slight extent to give H+ in solution acetic and formic acid CH3COOH, CH2O Bases : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Bases Strong bases - react completely with water to give OH ions. sodium hydroxide Weak bases - react only slightly with water to give OH ions. ammonia Slide 15: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Figure 4.6: HCl(aq) is completely ionized. Slide 16: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 Figure 4.7: An aqueous solution of sodium hydroxide. Slide 17: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 Figure 4.8: Acetic acid (HC2H3O2) exists in water mostly as undissociated molecules. Only a small percentage of the molecules are ionized. Molarity : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 Molarity Molarity (M) = moles of solute per volume of solution in liters: Common Terms of Solution Concentration : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 Common Terms of Solution Concentration Stock - routinely used solutions prepared in concentrated form. Concentrated - relatively large ratio of solute to solvent. (5.0 M NaCl) Dilute - relatively small ratio of solute to solvent. (0.01 M NaCl): (MV)initial=(MV)Final Slide 20: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20 Figure 4.10: Steps involved in the preparation of a standard aqueous solution. Slide 21: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 Figure 4.12: Dilution Procedure (a) A measuring pipet is used to transfer 28.7mL of 17.4 M acetic acid solution to a volumetric flask. (b) Water is added to the flask to the calibration mark. (c) The resulting solution is 1.00 M acetic acid. Types of Solution Reactions : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 Types of Solution Reactions Precipitation reactions AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq) Acid-base reactions NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l) Oxidation-reduction reactions Fe2O3(s) + Al(s) Fe(l) + Al2O3(s) Simple Rules for Solubility : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23 Simple Rules for Solubility 1. Most nitrate (NO3) salts are soluble. 2. Most alkali (group 1A) salts and NH4+ are soluble. 3. Most Cl, Br, and I salts are soluble (NOT Ag+, Pb2+, Hg22+) 4. Most sulfate salts are soluble (NOT BaSO4, PbSO4, HgSO4, CaSO4) 5. Most OH salts are only slightly soluble (NaOH, KOH are soluble, Ba(OH)2, Ca(OH)2 are marginally soluble) 6. Most S2, CO32, CrO42, PO43 salts are only slightly soluble. Slide 24: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 24 Figure 4.13: When yellow aqueous potassium chromate is added to a colorless barium nitrate solution, yellow barium chromate precipitates. Describing Reactions in SolutionPrecipitation : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 25 Describing Reactions in SolutionPrecipitation 1. Molecular equation (reactants and products as compounds) AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq) 2. Complete ionic equation (all strong electrolytes shown as ions) Ag+(aq) + NO3 (aq) + Na+ (aq) + Cl(aq) AgCl(s) + Na+ (aq) + NO3 (aq) Describing Reactions in Solution (continued) : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 26 Describing Reactions in Solution (continued) 3. Net ionic equation (show only components that actually reacts) Ag+(aq) + Cl(aq) AgCl(s) Na+ and NO3 are spectator ions. Slide 27: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 27 Acid-Base Reactions An acid produces H+ ions in water A base produces OH- ions in water An acid is a proton donor A base is a proton acceptor Arrhenius’s concept Bronsted & Lowrys’ concept Performing Calculations for Acid-Base Reactions : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 28 Performing Calculations for Acid-Base Reactions 1. List initial species and predict reaction. 2. Write balanced net ionic reaction. 3. Calculate moles of reactants. 4. Determine limiting reactant. 5. Calculate moles of required reactant/product. 6. Convert to grams or volume, as required. Remember: n H+ = n OH- (MV) H+ = (MV) OH- Neutralization Reaction : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 29 Neutralization Reaction 4.3 Key Titration Terms : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 30 Key Titration Terms Titrant - solution of known concentration used in titration Analyte - substance being analyzed Equivalence point - enough titrant added to react exactly with the analyte Endpoint - the indicator changes color so you can tell the equivalence point has been reached. movie Oxidation-Reduction Reactions : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 31 Oxidation-Reduction Reactions (electron transfer reactions) Oxidation half-reaction (lose e-) Reduction half-reaction (gain e-) Slide 32: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 32 Redox Reactions : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 33 Redox Reactions Many practical or everyday examples of redox reactions: Corrosion of iron (rust formation) Forest fire Charcoal grill Natural gas burning Batteries Production of Al metal from Al2O3 (alumina) Metabolic processes combustion Rules for Assigning Oxidation States : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 34 Rules for Assigning Oxidation States 1. Oxidation state of an atom in an element = 0 2. Oxidation state of monatomic element = charge 3. Oxygen = 2 in covalent compounds (except in peroxides where it = 1) 4. H = +1 in covalent compounds 5. Fluorine = 1 in compounds 6. Sum of oxidation states = 0 in compounds Sum of oxidation states = charge of the ion Slide 35: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 35 Slide 36: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 36 Zn is oxidized Cu2+ is reduced Zn is the reducing agent Cu2+ is the oxidizing agent 4.4 Ag+ is reduced Ag+ is the oxidizing agent Slide 37: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 37 NaIO3 Na = +1 O = -2 3x(-2) + 1 + ? = 0 I = +5 IF7 F = -1 7x(-1) + ? = 0 I = +7 K2Cr2O7 O = -2 K = +1 7x(-2) + 2x(+1) + 2x(?) = 0 Cr = +6 4.4 Balancing by Half-Reaction Method : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 38 Balancing by Half-Reaction Method 1. Write separate reduction, oxidation reactions. 2. For each half-reaction: Balance elements (except H, O) Balance O using H2O Balance H using H+ Balance charge using electrons Balancing by Half-Reaction Method (continued) : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 39 Balancing by Half-Reaction Method (continued) 3. If necessary, multiply by integer to equalize electron count. 4. Add half-reactions. 5. Check that elements and charges are balanced. Half-Reaction Method - Balancing in Base : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 40 Half-Reaction Method - Balancing in Base 1. Balance as in acid. 2. Add OH that equals H+ ions (both sides!) 3. Form water by combining H+, OH. 4. Check elements and charges for balance. Balancing Redox Equations : Copyright©2000 by Houghton Mifflin Company. All rights reserved. 41 Balancing Redox Equations Example: Balance the following redox reaction: Cr2O72- + Fe2+ Cr3+ + Fe3+ (acidic soln) 1) Break into half reactions: Cr2O72- Cr3+ Fe2+ Fe3+ Slide 42: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 42 Balancing Redox Equations Slide 43: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 43 Balancing Redox Equations 2) Balance each half reaction (cont) Slide 44: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 44 Balancing Redox Reactions 3) Multiply by integer so e- lost = e- gained Slide 45: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 45 Balancing Redox Reactions 3) Multiply by integer so e- lost = e- gained 6 Fe2+ 6 Fe3+ + 6 e- 6 e- + Cr2O72- + 14 H+ 2 Cr3+ + 7 H2O 4) Add both half reactions Cr2O72- + 6 Fe2+ + 14 H+ 2 Cr3+ + 6 Fe3+ + 7 H2O Slide 46: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 46 Balancing Redox Reactions Cr2O72- + 6 Fe2+ + 14 H+ 2 Cr3+ + 6 Fe3+ + 7 H2O 5) Check the equation 2 Cr 2 Cr 7 O 7 O 6 Fe 6 Fe 14 H 14 H +24 + 24 Slide 47: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 47 Balancing Redox Reactions Procedure for Basic Solutions: Divide the equation into 2 incomplete half reactions one for oxidation one for reduction Slide 48: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 48 Balancing Redox Reactions Balance each half-reaction: balance elements except H and O balance O atoms by adding H2O balance H atoms by adding H+ add 1 OH- to both sides for every H+ added combine H+ and OH- on same side to make H2O cancel the same # of H2O from each side balance charge by adding e- to side with greater overall + charge different Slide 49: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 49 Balancing Redox Equations Multiply each half reaction by an integer so that # e- lost = # e- gained Add the half reactions together. Simply where possible by canceling species appearing on both sides of equation Check the equation # of atoms total charge on each side Slide 50: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 50 Balancing Redox Reactions Example: Balance the following redox reaction. NH3 + ClO- Cl2 + N2H4 (basic soln) NH3 N2H4 ClO- Cl2 1) Break into half reactions: Slide 51: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 51 Balancing Redox Reactions 2) Balance each half reaction: + 2 OH- + 2 OH- Slide 52: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 52 Balancing Redox Reactions 2) Balance each half reaction: Slide 53: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 53 Balancing Redox Reactions 3) Multiply by integer so # e- lost = # e- gained 2 NH3 + 2 OH- N2H4 + 2 H2O + 2 e- 2 e- + 2 ClO- + 2 H2O Cl2 + 4 OH- 4) Add both half reactions 2 NH3 + 2 OH- + 2ClO- + 2 H2O N2H4 + 2 H2O + Cl2 + 4 OH- Slide 54: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 54 Balancing Redox Reactions 5) Cancel out common species 2 NH3 + 2 OH- + 2 ClO- + 2 H2O N2H4 + 2 H2O + Cl2 + 4 OH- 2 6) Check final equation: 2 N 2 N 6 H 6 H 2 Cl 2 Cl 2 O 2 O -2 -2 Slide 55: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 55 Slide 56: Copyright©2000 by Houghton Mifflin Company. All rights reserved. 56