4-1 Dissolution Reactions 4-2 Precipitation Reactions 4-3 Acids and Bases and Their Reactions 4-4 Oxidation-Reduction Reactions

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1 5/20/2003 FB Chapter 4 3 5/20/2003 FB Chapter 4 4 Chapter 4 Types of Chemical Reactions 4-1 Dissolution Reactions 4-2 Precipitation Reactions 4-3 Acids and Bases and Their Reactions 4-4 xidation-reduction Reactions 5/20/2003 FB Chapter Dissolution Ionic Compounds in Water Molecular Compounds in Water Electrolytes and Non-Electrolytes Solubilities (like dissolves like) Predicting Dissolution Reactions 2. Precipitation Reactions Ionic Equations and Net Ionic Equations Predicting Precipitation Reactions 3. Acids and Bases Arrhenius Acids and Bases Theory Strong and Weak acid Naming Acids Weak Bases Modifying the Arrhenius model Acid-Base Titrations 4. xidation-reduction Reactions (Redox) Reactions xidizing and Reducing Agents xidation Number Types of Redox Reactions» Combination and Decomposition» xygenation» ydrogenation» Displacement Reactions 5/20/2003» Disproportionation FB Chapter 4 2 Dissolution: Solution: Solvent: Solute: Two (or more) substances spread out, or disperse, into each other at the level of individual atoms, molecules, or ions. Ionic Compounds in Water: All ionic compounds are solids in the range of temperature in which water is a liquid. They have rigid lattices in which strong forces (ionic bonds) pin the constituent ions in place. The high melting points of ionic compounds indicate that a good deal of energy must be supplied to destroy the lattice and produce a liquid (molten) form in which the ions move more freely. Aquation: In principle, the solute and solvent can be any combination of solid (s), liquid (l), and gaseous (g) phases.

2 Ionic Compounds in Water: 5/20/2003 FB Chapter 4 7 Molecular Compounds in Water: 5/20/2003 FB Chapter 4 8 Solute is said to dissociate into ions or to ionize upon dissociation. Molecular substances (covalent) contain no ions to which water molecules can adhere, but their molecules are often polar. Example: members of the class of carbohydrates known as sugars have the general formula, C m ( 2 ) n. Typical sugars include sucrose, C (table sugar); fructose, C (fruit sugar); and ribose, C (a subunit in the biomolecules ribonucleic acids). C (s) C (aq) 5/20/2003 FB Chapter 4 5 5/20/2003 FB Chapter 4 6 Solubilities: Miscible: Solubility: The largest amount that can dissolve in a given amount of a solvent at a particular temperature. Pairs of liquids that mix in any proportion are termed miscible. Liquids that do not mix are termed immiscible "Like dissolves like" in other words, substances with similar intermolecular attractive forces tend to be soluble in one another

3 5/20/2003 FB Chapter /20/2003 FB Chapter 4 12 like dissolves like concept C like dissolves like concept = = glucose octane C 2 water isobutane ethanol N 2 alanine fructose benzene cyclohexane octanol 5/20/2003 FB Chapter 4 9 sucrose Cl Cl Cl Non-Polar Cl carbon tetrachloride 5/20/2003 FB Chapter 4 10 Electrolytes and Non-Electrolytes: Predicting Dissolution Reactions Electrolytes: Non-Electrolytes: Strong electrolytes:

4 5/20/2003 FB Chapter /20/2003 FB Chapter 4 16 Solubilities: Exercise 4-1: Predict whether the following substances are soluble in water: (a) calcium carbonate (CaC 3 ) (b) mercury(ii) sulfide (gs) (c) isopropanol (C 3 7 ) 5/20/2003 FB Chapter Dissolution Ionic Compounds in Water Molecular Compounds in Water Electrolytes and Non-Electrolytes Solubilities (like dissolves like) Predicting Dissolution Reactions 2. Precipitation Reactions Ionic Equations and Net Ionic Equations Predicting Precipitation Reactions 3. Acids and Bases Arrhenius Acids and Bases Theory Strong and Weak acid Naming Acids Weak Bases Modifying the Arrhenius model Acid-Base Titrations 4. xidation-reduction Reactions (Redox) Reactions xidizing and Reducing Agents xidation Number Types of Redox Reactions» Combination and Decomposition» xygenation» ydrogenation 5/20/2003» Displacement Reactions FB Chapter 4» Disproportionation 14 CEM1310 McKelvy Lecture Solubility Rules 1. All common sodium, potassium and ammonium salts are soluble in water 2. The chloride and iodide salts of all common metals, except silver, lead and mercury (I), are soluble in water. Lead chloride is soluble in hot water. 3. The sulfates of all metals, excepts lead, mercury (I), barium, strontium, and calcium are soluble in water. 4. The carbonates of all metals, except those of Group 1A and ammonium carbonate, are insoluble in water 5. Most metal hydroxides are insoluble in water. owever, the hydroxides of group 1A are soluble and those of Group IIA are moderately soluble.

5 Precipitation Reactions: Ionic Equations and Net Ionic Equations: Whenever the concentration of a substance in solution exceeds its solubility, a new phase starts to separate. A new solid phase is usually dense enough to sink to the bottom of a liquid solution. Solids usually precipitate ( fall down ) from their solution. BaCl 2 (aq) + K 2 S 4 (aq) BaS 4 (s) + 2 KCl(aq) Ionic equation Spectator ions Net ionic equation 5/20/2003 FB Chapter /20/2003 FB Chapter 4 18 Exercise 4-2: Write a net ionic equation to represent the formation of the precipitate observed when aqueous solutions of CaCl 2 and NaF are mixed. Identify the spectator ions in this process. 5/20/2003 FB Chapter Dissolution Ionic Compounds in Water Molecular Compounds in Water Electrolytes and Non-Electrolytes Solubilities (like dissolves like) Predicting Dissolution Reactions 2. Precipitation Reactions Ionic Equations and Net Ionic Equations Predicting Precipitation Reactions 3. Acids and Bases Arrhenius Acids and Bases Theory Strong and Weak acid Naming Acids Weak Bases Modifying the Arrhenius model Acid-Base Titrations 4. xidation-reduction Reactions (Redox) Reactions xidizing and Reducing Agents xidation Number Types of Redox Reactions» Combination and Decomposition» xygenation» ydrogenation 5/20/2003» Displacement Reactions FB Chapter 4 20

6 5/20/2003 FB Chapter /20/2003 FB Chapter 4 24 Acids and Bases and Their Reactions Acids and Bases and Their Reactions: Acid Base Theory 1. Arrhenius Acids and Bases (Chapter 4) Acids are + donors Bases are - donors 2. Arrhenius Broadened Definition (Chapter 4) Acids increase + concentration or [ + ] increases Bases increase - concentration or [ - ] increases 3. Brønsted Acids and Bases (Chapter 8) Acids donate + Bases accept + 4. Lewis Acids and Bases (Chapter 8) Acids are electron pair acceptors Bases are electron pair donors R C 5/20/2003 FB Chapter /20/2003 FB Chapter 4 22 Arrhenius Acids and Bases: Arrhenius Acids and Bases: Strong acids: n Arrhenius acid is a substance that, when dissolved in water, elivers hydrogen ions ( + (aq) ions) to the solution; it is a ydrogen-ion donor. n Arrhenius base is a substance that, when dissolved in water, elivers hydroxide ions ( - (aq) ions) to the solution; it is a ydroxide-ion donor. Strong bases: ater is simultaneously and equally both an acid and a base:

7 Arrhenius Acids and Bases: 5/20/2003 FB Chapter 4 27 Weak Acids 5/20/2003 FB Chapter 4 28 Neutralization reaction: Cl(aq) + Na(aq) 2 (l) + NaCl(aq) C 3 C(aq) C 3 C - (aq) + + (aq) (dissociation of acetic acid) C 3 C(aq) + Na(aq) NaC 3 C(aq) + 2 (l) (overall equation) 5/20/2003 FB Chapter /20/2003 FB Chapter 4 26 Naming Acids Binary acids: Cl as covalent compound is hydrogen chloride Cl as a binary acid is hydrochloric Acid xoacids: xoacids: S -2 4 or Sulfate ion S -2 3 or Sulfite ion 2 S 4 becomes Sulfuric Acid 2 S 3 becomes Sulfurous Acid Modifying the Arrhenius Model An Arrhenius base is a substance that, when dissolved in water, increases the concentration of hydroxide ions over what is present in the pure solvent. An Arrhenius acid is a substance that, when dissolved in water, increases the concentration of hydrogen ions over what is present in the pure solvent. rganic acids: C - or Formate ion becomes Formic Acid (R=) R C

8 Acid-Base Titrations 5/20/2003 FB Chapter /20/2003 FB Chapter 4 32 Titration: A controlled addition of measured volumes of a solution of known concentration to a second solution of unknown concentration under conditions in which the solutes react cleanly (without side reactions), completely, and rapidly. A titration is complete when the second solute is used up. Completion is signaled by a change in some physical property, such as the color of the reacting mixture or the color of an indicator that has been added to it. [Na] X Indicator phenolphthalein 5/20/2003 FB Chapter /20/2003 FB Chapter 4 30 Exercise 4-6 Compute the molarity of a solution of sodium hydroxide if ml of solution must be added to a solution containing g of KC (potassium hydrogen phthalate abbreviated KP) to reach the phenolphthalein end-point. Exercise 4-4 Give the name for the acid 2 Se 3. Write the overall, ionic, and net ionic equations for the complete neutralization of 2 Se 3 by sodium hydroxide. Start with something we know: Selenium (Se) is in Group VI with Sulfur (S) 2 S 4 is Sulfuric Acid and 2 S 3 is Sulfurous Acid

9 5/20/2003 FB Chapter /20/2003 FB Chapter 4 36 Acids and Bases and Their Reactions Acid Base Theory 1. Arrhenius Acids and Bases (Chapter 4) Acids are + donors Bases are - donors 2. Arrhenius Broadened Definition (Chapter 4) Acids increase + concentration or [ + ] increases Bases increase - concentration or [ - ] increases 3. Brønsted Acids and Bases (Chapter 8) Acids donate + Bases accept + 4. Lewis Acids and Bases (Chapter 8) Acids are electron pair acceptors Bases are electron pair donors 5/20/2003 FB Chapter Dissolution Ionic Compounds in Water Molecular Compounds in Water Electrolytes and Non-Electrolytes Solubilities (like dissolves like) Predicting Dissolution Reactions 2. Precipitation Reactions Ionic Equations and Net Ionic Equations Predicting Precipitation Reactions 3. Acids and Bases Arrhenius Acids and Bases Theory Strong and Weak acid Naming Acids Weak Bases Modifying the Arrhenius model Acid-Base Titrations 4. xidation-reduction Reactions (Redox) Reactions xidizing and Reducing Agents xidation Number Types of Redox Reactions» Combination and Decomposition» xygenation» ydrogenation 5/20/2003» Displacement Reactions FB Chapter 4» Disproportionation 34 xidation-reduction or Redox Reactions Definitions xidation and Reduction xidation Numbers Types of Redox Reactions Combination Decomposition xygenation ydrogenation Displacement Disproportionation xidation-reduction Reactions Redox: an extensive and important class of reactions that is characterized by the transfer of electrons. 2 Mg(s) + 2 (g) 2 Mg(s) Magnesium is oxidized: it gives up electrons as the charge on its atoms increases from zero to +2. xygen is reduced: it gains electrons as the charge on its atoms decreases from zero to -2 (i.e., becomes more negative).

10 5/20/2003 FB Chapter /20/2003 FB Chapter 4 40 xidation Numbers (also called oxidation states) are determined for the atoms in covalently bonded compounds by applying the following set of simple rules: 1. The oxidation number of the atoms in a neutral molecule must all up to zero; those in an ion must add up to the charge on the ion. 2. Alkali metal (Group I) atoms have oxidation number +1, and alkaline earth (Group II) atoms have oxidation number +2 in their compounds; atoms of Group III elements usually have oxidation number +3 in their compounds. 3. Fluorine always has an oxidation number of -1 in its compounds. The other halogens have oxidation number -1 in their compounds, except in compounds with oxygen and with other halogens, in which they can have positive oxidation numbers. xidation Numbers (also called oxidation states) are determined for the atoms in covalently bonded compounds by applying the following set of simple rules: 4. ydrogen is assigned an oxidation number of +1 in its compounds, except in metal hydrides such as Li, in which rule 2 take precedence and hydrogen has an oxidation number of xygen is assigned an oxidation number of -2 in compounds. There are two exceptions: in compounds with fluorine, rule 3 takes precedence, and in compounds that contain bonds, rules 2 and 4 take precedence. Thus, the oxidation number of oxygen in F 2 is +2; in peroxides (e.g., 2 2 and Na 2 2 ), its oxidation number is -1, and in superoxides(e.g., K 2 ), its oxidation number is -½. 5/20/2003 FB Chapter /20/2003 FB Chapter 4 38 What is the Nitrogen Atom xidation State? Assign xidation Numbers to each of the following N 2-1 N 2 N 2 int consider as - Ethane C 2 6 Acetic Acid C N 2 +1 Ammonium Nitrate N 4 N 3 int: N 4 +1 N 3-1 N 3-1 Potassium superoxide K 2

11 5/20/2003 FB Chapter /20/2003 FB Chapter 4 44 We can now state the following definition An atom is oxidized (loses electrons) if its oxidation number increases in a chemical reaction; an atom is reduced (gains electrons) if its oxidation number decreases. Term xidation Reduction xidizing Agent, does the oxidizing Reducing Agent, does the reducing Substance xidized Substance Reduced xidation Number Change Increase Decrease Decrease Increase Increase Decrease Electron Change Loss of Electrons Gain of Electrons Picks Up electrons Supplies Electrons Loses Electrons Gains Electrons 5/20/2003 FB Chapter /20/2003 FB Chapter 4 42 xidation-reduction reactions Term xidation Number Change Electron Change xidizing Agent, does the oxidizing Decrease Picks Up electrons Reducing Agent, does the reducing Increase Supplies Electrons Substance xidized Increase Loses Electrons Substance Reduced Decrease Gains Electrons Cl 2 Na NaCl + Mg Mg xidation-reduction or Redox Reactions Definitions xidation and Reduction xidation Numbers Types of Redox Reactions Combination Decomposition xygenation ydrogenation Displacement Disproportionation

12 5/20/2003 FB Chapter /20/2003 FB Chapter 4 48 Types of Redox Reactions Redox Combination and Decomposition Reactions P 4 (s) + 6 Cl 2 (g) 4 PCl 3 (l) P 4 (s) + 10 Cl 2 (g) 4 PCl 5 (l) Types of Redox Reactions xygenation and ydrogenation 4 Li (s) + 2 (g) 2 Li 2 (s) 2 ZnS(s) (g) 2 Zn(s) + 2 S 2 (g) 2 g (s) 2 g(l) + 2 (g) 2 g 2 (s) 4 g(l) + 2 (g) 2 Na(l) + 2 (g) 2 Na(s) Fe 2 3 (s) (g) 2 Fe(s) (g) (l) 2 2 (l) + 2 (g) 5/20/2003 FB Chapter /20/2003 FB Chapter 4 46 Types of Redox Reactions Displacement Reactions Types of Redox Reactions Disproportionation 2 AgN 3 (aq) + Cu(s) Cu(N 3 ) 2 (aq) + 2 Ag(s) (overall equation) 2 Ag + (aq) + Cu(s) Cu 2+ (aq) + 2 Ag(s) (net ionic equation) Referring to the information (page 178) of Ability to Replace (l) 2 2 (l) + 2 (g) 2 Cu + (aq) Cu 2+ (aq) + Cu(s) (net ionic equation) Cl 2 (g) + 2 KI(aq) I 2 (s) + 2 KCl(aq) Cl 2 (g) + 2 I - (aq) I 2 (s) + 2 Cl - (aq) (overall equation) (net ionic equation)

13 1. Dissolution Ionic Compounds in Water Molecular Compounds in Water Electrolytes and Non-Electrolytes Solubilities (like dissolves like) Predicting Dissolution Reactions 2. Precipitation Reactions Ionic Equations and Net Ionic Equations Predicting Precipitation Reactions 3. Acids and Bases Arrhenius Acids and Bases Theory Strong and Weak acid Naming Acids Weak Bases Modifying the Arrhenius model Acid-Base Titrations 4. xidation-reduction Reactions (Redox) Reactions xidizing and Reducing Agents xidation Number Types of Redox Reactions» Combination and Decomposition» xygenation» ydrogenation 5/20/2003» Displacement Reactions FB Chapter 4» Disproportionation 49 Chapter 4: Types of Chemical Reactions Examples and Exercises: omework: All (4-1 to 4-12) 1, 6, 12, 50, 54, 55, 59, 71 Acknowledgement: Many of the slide used in this Chapter were originally prepared by Dr. George McKelvy 5/20/2003 FB Chapter 4 50