chapter16_Fall2011_3slides_perpage

chapter16_Fall2011_3slides_perpage - 10/1/2011 Chapter 16...

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10/1/2011 1 1 Acid-Base Equilibria Chapter 16 Acids and Bases 1. Acids and Bases: A Brief Review 2. Brønsted-Lowry Acids and Bases 3. The Autoionization of Water 4. The pH Scale 5. Strong Acids and Bases 6. Weak Acids 7. Weak Bases 8. Relationship between K a and K b 9. Acid-Base Properties of Salt Solutions 10. Acid-Base Behavior and Chemical Structure 11. Lewis Acids and Bases 2 Overview The Arrhenius definition is the narrowest view of acids and bases and Lewis theory is the broadest definition. Arrhenius Brønsted Lewis In this chapter, you will develop an increasingly more general view of acid/base reactivity. 3 1. Acids and Bases: Review Arrhenius Acids and Bases: Arrhenius acid = a substance that directly yields H + ions when dissolved in water. Arrhenius base = a substance that directly yields OH - ions when dissolved in water. Ex: HCl( aq ) → → Cl - ( aq ) + H + ( aq ) NaOH( aq ) → → OH - ( aq ) + Na + ( aq ) In aqueous solution, protons (H + ) bond through covalent and hydrogen bonds to water molecules (forming H 3 O + ).
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10/1/2011 2 4 But…. • We know that aqueous NH 3 tests basic (wet litmust paper), but it does not satisfy the narrow definition given of an Arrhenius base. • We need a broader definition! • What’s missing? Arrhenius Brønsted Lewis One obvious answer is the role of water: NH 3 (aq) + H 2 O ( ) NH 4 + (aq) + OH - (aq) Better, but even in the absence of water…. ... NH 3 (aq) + HCl (aq) NH 4 + (aq) + Cl - (aq) What do these reactions have in common? 5 2. Brønsted-Lowry Acid-Base Definition An acid-base reaction can now be viewed from the standpoint of the reactants AND the products. An acid reactant will produce a base product and the two will constitute an acid -base conjugate pair . An acid is a proton donor, any species which donates a H + . A base is a proton acceptor, any species which accepts a H + . 6 Proton transfer as the essential feature of Brønsted acid-base reactions. HCl + Cl - + NH 3 NH 4 + (base, H + acceptor) (acid, H + donor) NH 3 + NH 4 + + Lone pair binds H + OH - (acid, H + donor) (base, H + acceptor) H 2 O
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10/1/2011 3 7 Conjugate Acid-Base Pairs Conjugate acid-base pair = two species whose formulas differ by a single H + Examples: HCN / CN - H 2 O / H 3 O + H 2 O / OH - Conjugate acid = a species with one more H + than its conjugate base Conjugate base = a species with one fewer H + than its conjugate acid 8 1) What is the conjugate acid of each of the following: (a) HS - (b) H 2 NNH 2 (c) SO 4 2- Solution: 2) What is the conjugate base of each of the following: (a) (b) (c) Solution: (b) (c) (a) (a) (c) H 2 SO 4 (c) (b) 2 NH 3 (b) Practice Identifying Conjugate Acid/Bases 9 Strong acids are strong electrolytes: ) ( ) ( H 100% ) ( H ) ( 3 2 aq NO aq O l O aq HNO - + + + 3 3 Weak acids are weak electrolytes: ) ( F ) ( O H ) O( H ) HF( - 3 % 1 ~ 2 aq aq l aq +  → + + Relative Acid-Base Strength in Water
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This note was uploaded on 10/11/2011 for the course CHEM 012 taught by Professor Mounaamaalouf,reneescole, during the Spring '11 term at Iowa State.

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chapter16_Fall2011_3slides_perpage - 10/1/2011 Chapter 16...

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