Chapter 4 - Chapter 4: Major Classes of Chemical Reactions...

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Slide No. 1 Chapter 4: Major Classes of Chemical Reactions ± Water as a solvent ² Electrolytes ² Polar nature of water ± Precipitation Reactions ² Predicting the products ² Net ionic equations ± Acid-Base Reactions ² Strong and weak acids and bases ² Three reaction subclasses ± Reading: Sections 4.1-4.5 (4.6 and 4.7 are skipped); PLUS 18.2 ± Homework Problems: ² Chapter 4: 6(5), 18(19a,b), 29(30), 31(32), 33(34), 35(36), 45(46), 49(50), 60(61), 66(67), 68(69), 70(71), 74(75), 76(77). ² Chapter 18: 23, 25, 27, 29 Lecture Outline ± The pH Scale (Ch. 18.2) ± Oxidation-Reduction Reactions ² Terminology ² Complex redox reactions ² Oxidation numbers ± Titrations Slide No. 2 4.1 Aqueous Reactions: Water as a solvent ± Many important reactions take place in water. ² biological reactions ² most of our planet covered by water: oceans, rivers, streams ² water = solvent ; dissolved substances = solute . HCl (aq) + NaOH (aq) Æ NaCl (aq) + H 2 O (l) ± Three classes of typical aqueous reactions ² Precipitation ² Acid-Base (Neutralization) ² Redox (Oxidation-Reduction)
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Slide No. 3 Electrolytes ± By dissolving certain substances, water can be made to _______ electricity. ² NaCl (aq) ² HCl ² HCH 3 CO 2 (aq) ± Why do aqueous solutions of some compounds conduct an electric current but others do not? ² Some compounds ionize in solution ² Mobile ions in solution conduct electrical current (see next slide) 4.1 Aqueous Reactions: Water as a solvent Slide No. 4 Electrolytes No Ions = No Current Ions are not mobile Mobile ions
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Slide No. 5 COVALENT compounds in Aqueous Solution CH 3 OH (methanol) ± Covalent bonds are not disrupted by dissolving in a solvent ± Molecules – but not atoms – are separated upon dissolving NON-ELECTROLYTES C H H H O H 4.1 Aqueous Reactions: Water as a solvent ± Molecules held together by covalent bonds ² Shared electrons hold atoms together ± In pure substances (not dissolved in water), additional weak forces result in interactions between molecules (______________ interactions) ² "hydrogen bonds" ² dipolar and Van der Waals forces Slide No. 6 IONIC Compounds in Aqueous Solution K 2 SO 4 (potassium sulfate) ± Solid held together by ionic bonds ² Mutual electrostatic attraction of opposite charges ± Upon dissolving, ions separate ² Held apart by solvent: interactions with solvent stronger than between the ions ² Solvent surrounds ions (see Slide 9) ± Polyatomic ions remain intact ² The atoms in the sulfate (SO 4 2– ) anions are held together by covalent bonds + + + + + + + + + + + + - - - - - - + + + + + + + + + + - - - - - STRONG ELECTROLYTE 4.1 Aqueous Reactions: Water as a solvent
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Slide No. 7 Acids in Aqueous Solution HCl (hydrochloric acid) ± In pure substance, molecules held together by covalent bonds ² Shared electrons HC l - - - - - HCl: STRONG ELECTROLYTE Completely ionized - - HF: WEAK ELECTROLYTE Partially ionized 4.1 Aqueous Reactions: Water as a solvent ± Upon dissolving in water, molecules dissociated into ions (“strong acids”) ² Held apart by solvent ² Solvent surrounds ions (see Slide 9) ± Polyatomic ions remain intact ² Example: HNO 3 Æ H + + NO 3 - (the nitrate ion remains intact) ± "Weak" acids (e.g., HF, HC 2 H 3 O 2 , HCN) only dissociate partially ±
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Chapter 4 - Chapter 4: Major Classes of Chemical Reactions...

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