CHAPTER 16 Notes.doc - CHAPTER SIXTEEN ACID-BASE EQUILIBRIA https\/www.ncbi.nlm.nih.gov\/pmc\/articles\/PMC5830292 Acids and Bases a Brief Review Acids 1

CHAPTER 16 Notes.doc - CHAPTER SIXTEEN ACID-BASE EQUILIBRIA...

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CHAPTER SIXTEEN ACID-BASE EQUILIBRIA Acids and Bases a Brief Review Acids: 1. have sour taste 2. turn blue litmus paper red 3. acid comes from a Latin word meaning “sour or tart” 4. all acids contain hydrogen Bases: 1. have bitter taste 2. feel slippery 3. base comes from old English word “debase” to bring low. Arrhenius Definition: Acids are substances that when dissolved in water, increase the concentration of H + ions in solution. Examples: Bases are substances that when diss olved in water increase the concentration of OH - ions Examples: 1
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Brønsted-Lowery Acids and Bases Limitations of Arrhenius acids and bases -restricted to aqueous solutions and solutions and protonic solvents. The H + Ion in Water H + + O–H H–O–H H H H + H 3 O + Proton Transfer Reactions: HCl (g) + H 2 O (l) H 3 O +(aq) + Cl - (aq) Brønsted-Lowery Acid is a substance (molecule or ion) that can donate a proton to another substance. Brønsted-Lowery Base a substance that can accept a proton. 2
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H H Cl-H + :N-H H-N-H + Cl - H H NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) NH 3 is an Arrhenius base. Why? NH 3 is a Brønsted base. Why? Conjugate Acid-Base Pairs HX (aq) + H 2 O (l) X - (aq) + H 3 O + (aq) Conjugate acid –base pair differ only in the presence or absence of a proton. HNO 2 (aq) + H 2 O (l) NO 2 - (aq) + H 3 O + (aq) NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) NH 4 + (aq) + CN - (aq) HCN (aq) + NH 3 (aq) 3
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(CH 3 ) 3 N + H 2 O (CH 3 ) 3 NH + + OH - Relative Strengths of Acids and Bases The stronger an acid, the weaker is its conjugate base; the stronger a base; the weaker its conjugate acid. HCl strong acid Cl - weak conjugate base. (Figure 16.4), page 674. HCl (g) + H 2 O (l) → H 3 O + (aq) + Cl - (aq) Cl - is weaker base than H 2 O so it gets the proton; equilibrium lies right. Consider the following reactions and determine the direction of the equilibrium: HC 2 H 3 O 2 + H 2 O H 3 O + + C 2 H 3 O 2 - HPO 4 2- + H 2 O(l) H 2 PO 4 - + OH - NH 4 + + OH - NH 3 + H 2 O 4
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The Autoionization of Water H-O + H-O → H-O-H + OH - H H H 2 H 2 O (l) H 3 O + (aq) + OH - (aq) The Ion-Product of Water K c = [H 3 O + ] [OH - ] Since we are considering water, K c is given the symbol K w . K w = [H 3 O + ][OH - ] = 1 x 10 -14 at 25 ºC K w = [H 3 O + ][OH - ] = [H + ][OH - ] K w = [H 3 O + ][OH - ] = 1 x 10 -14 H 2 O (l) [H + ] + [OH - ] x x = (x)(x) = 1 x 10 -14 5
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x = 1 x 10 -7 = [H + ] = [OH - ] Neutral [H + ] = 1 x 10 -7 Acid [H + ] > 1 x 10 -7 Base [H + ] < 1 x 10 -7 Consider: [H+] = 1.2 x 10 -8 [OH-] = 1 x 10 -7 [OH-] = 8.3 x 10 -12 [H+] = 1.35 x 10 -3 Calculate the [OH - ] concentration if , [H + ] =2.5 x 10 -5 The pH Scale Since the H + is very small another way to express hydrogen ion concentration was needed. The solution was the pH scale.
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