chapter 15 notes

chapter 15 notes - ©2010 Donald L Siegel All Rights...

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Unformatted text preview: ©2010 Donald L. Siegel, All Rights Reserved Chapter 15 Chapter 15 Acids, Bases and Acid-Base Equilibria ©2010 Donald L. Siegel, All Rights Reserved What are acids and bases? What are acids and bases? W Arrhenius Acids produce H + in solution Bases produce OH- in solution Too limited W Brønsted-Lowery Acid: proton donor Base: proton acceptor Still limited W Lewis Acids and bases Acid: electron pair acceptor Base: electron pair donor Too broad? ©2010 Donald L. Siegel, All Rights Reserved Conjugate Conjugate acd acd-- base pairs base pairs W Under the Brønsted-Lowery model, each acid has a conjugate pair base (other side of reaction) W Example NH 3 (aq) + H 2 O(l) ⇌ NH 4 + (aq) + OH- (aq) Base Acid Conj. Acid Conj. Base ©2010 Donald L. Siegel, All Rights Reserved K K a a W Acids dissociate in water, to some extent HA(aq) ⇌ H + (aq) + A- (aq) [ ][ ] [ ] HA A H K a − + = ©2010 Donald L. Siegel, All Rights Reserved Acid Strength Acid Strength W Strong acids dissociate more than weak ones K a larger for stronger acids, reaction lies to the right Very strong acids dissociate completely Weak acids, equilbrium lies to the left W The stronger the acid, the weaker the conjugate base The conjugate base of a weak acid is a weak base. The conjugate base of a strong acid is a very weak base. ©2010 Donald L. Siegel, All Rights Reserved Types of acids Types of acids W Oxoacids Acidic H attached to O (except 1 in H 3 PO 3 ) Several are strong W Organic acids Contain carboxylic acid group COOH R C O O H ©2010 Donald L. Siegel, All Rights Reserved Autoionization Autoionization of water of water W Water can act as either an acid or a base. W To be an acid, it must be a stronger acid than water W The reaction against which we measure is H 2 O(l) ⇌ H + (aq) +OH- (aq) H 2 O + H 2 O ⇌ H 3 O + + OH- acid base acid base K w = [H + ][OH- ] = 1 × 10-14 at 25 ° C Pure water at 25 ° C, [H + ] = [OH- ] =1 × 10-7 M ©2010 Donald L. Siegel, All Rights Reserved pH pH W We are often dealing with weak acids W Even strong acids, [H + ] is frequently <0.001M W People are more comfortable with numbers between 1-10 W Express [H + ] as a –log, called pH potenz hydrogen-log 10 [H + ] pAnything ©2010 Donald L. Siegel, All Rights Reserved ©2010 Donald L. Siegel, All Rights Reserved More on pH More on pH W K w = 1 × 10-14 = [H + ][OH- ] W pK w = 14 = pH + pOH W Example: Find the pH and pOH of a 0.001M HCl(aq) solution pH = -log(0.001) = 3 pOH = 14 – 3 = 11 W Trick question: what is the pH of 1 × 10-9 M HCl(aq) pH = 7 ©2010 Donald L. Siegel, All Rights Reserved What What ’ ’ s in the solution? s in the solution? W Strong acids dissociate completely HCl(aq) contains only H + and Cl- W This makes calculating pH easy We don’t have to worry about the equilibrium between the dissociated and undissociated forms (K a ) ©2010 Donald L. Siegel, All Rights Reserved Acid Strength Acid Strength W Strong acids dissociate more than weak ones K a larger for stronger acids, reaction lies to the right...
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This note was uploaded on 11/09/2011 for the course CHEM 162 taught by Professor Siegal during the Spring '08 term at Rutgers.

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chapter 15 notes - ©2010 Donald L Siegel All Rights...

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