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Unformatted text preview: Chem 1151 chapter 4 Chemical Reactions in Aqueous Solutions I. Water, the common solvent H O is bent molecule 2 O end more negative than H end. Thus H O is a polar molecule. 2 Therefore many compounds are soluble in water. When ionic compounds dissolve in water the ions are hydrated. + KCl(s) K (aq) + Cl (aq) II. Compounds in Aqueous Solutions Strong Electrolytes: 100 % dissociated into ions, good conductors of electricity. Ex. Strong acids and bases, soluble ionic salts. Weak Electrolytes: partially dissociated into ions, weak conductors of electricity. Ex. Weak acids and bases. Nonelectrolytes: negligible dissociation into ions, poor conductors of electricity ex. Many molecular species, water A. Demo: Conductivity of Aqueous Solutions
Substance 1. HCl 2. NaOH 3. NH 3 4. HC H O (CH CO H) 2 3 2 3 2 5. NaCl 6. C H O 12 22 11 7. H O 2 Light bulb Type of Elect. B. Ionization of electrolytes 1. Strong electrolytes 100 % ionized + a. NaCl(s) > Na (aq) + Cl (aq) Ionic concentrations: [ ] = M Suppose 1 mole NaCl dissolved in 1 L solution: (1M NaCl) + [Na ] = 1 M, [Cl ] = 1 M [ions] = 2M +2 b. CaCl (s) > Ca (aq) + 2 Cl (aq) Given: 1 M CaCl 2 2 +2 [Ca ] = 1 M, [Cl ] = 2 M, [ions] = ? 3M 2. Weak electrolytes + HC H O (aq) <> H (aq) + C H O (aq) 2 3 2 2 3 2 Most weak electrolytes are about 5 % ionized or less. Therefore solution consists of both molecules and ions, primarily molecules 3. Nonelectrolytes: negligible ionization C H O (s) > C H O (aq) 12 22 11 12 22 11 C. Some reactions that occur in aqueous solution 1. Precipitation: soluble reactants produce 1 or more insoluble products that come out of solution. i.e. precipitate 2. Acid Base neutralization reactions 3. Oxidation Reduction reactions III. Composition of Solutions (sec. 4.3) A. Molarity: moles solute / liter of solution Units: moles / liter Several example problems done in class. B. Dilution of Solutions: M V = M V 1 1 2 2 Problems done in class. IV. Precipitation Reactions Two aqueous solutions are combined producing an insoluble solid (precipitate). Demo: Pb(NO ) + KI 3 2 Ionic Equations A. Example: Barium chloride(aq) + Sodium sulfate(aq) 1. Molecular (or formula) equation: BaCl (aq) + Na SO (aq)2 NaCl(aq) +BaSO (s) 2 2 4 4 2. Complete ionic equation: (aq) omitted for simplicity. All ions are in aqueous solution +2 1 +1 Ba + 2Cl + 2Na + SO 2 BaSO (s) + 4 4 1 +1 2Cl +2Na 3. Net ionic equation +2 Ba + SO 2 BaSO (s) 4 4 Demo: Add Pb(NO ) + KI to water 3 2 in petri dish. Observations: Ionic equation: Net ionic: Spectator ions: Why does reaction occur: B. Solubility Rules, p. 144 : Study Examples of precipitation reactions and net ionic equations will be done in class. C. Stoichiometry of Reactions in Aqueous Solution. Follow steps for solving stoichiometry problems, except use balanced net ionic equation to determine species present. Examples done in class. ...
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