Chap 18 - 1 18 Ionic Equilibria: Acids and Bases 2 A Review...

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Unformatted text preview: 1 18 Ionic Equilibria: Acids and Bases 2 A Review of Strong Electrolytes Weak acids and bases ionize or dissociate partially, typically 1-5% . Strong electrolytes (which includes strong acids and bases) ionize or dissociate completely ( they approach 100% dissociation in aqueous solutions). 3 A Review of Strong Electrolytes There are three classes of strong electrolytes. 1. Strong Water Soluble Acids HNO 3 + H 2 O H 3 O + + NO 3- or HNO 3 H + + NO 3- 4 A Review of Strong Electrolytes 5 A Review of Strong Electrolytes 2 Strong Water Soluble Bases Metal hydroxides of Group IA elements and Ca, Ba, and Sr of Group IIA KOH (s) + H 2 O ( l ) K + (aq) + OH- (aq) Sr(OH) 2(s) + H 2 O ( l ) Sr 2+ (aq) + 2 OH- (aq) 6 A Review of Strong Electrolytes 3 Most Water Soluble Salts The solubility guidelines from Chapter 4 will help you remember these salts. NaCl (s) + H 2 O ( l ) Na + (aq) + Cl- (aq) Ca(NO 3 ) 2(s) + H 2 O ( l ) Ca 2+ (aq) + 2 NO 3- (aq) 7 A Review of Strong Electrolytes The calculation of ion concentrations in solutions of strong electrolytes is easy. Example 18-1: Calculate the concentrations of ions in 0.050 M nitric acid, HNO 3 . HNO 3 + H 2 O H 3 O + + NO 3- initial 0.050 M 0 soln 0 0.050 M 0.050 M 8 A Review of Strong Electrolytes Example 18-2: Calculate the concentrations of ions in 0.020 M strontium hydroxide, Sr(OH) 2 , solution. Sr(OH) 2 + H 2 O Sr 2+ + 2 OH- initial 0.020 M 0 soln 0 0.020 M 2(0.020) M 0.040 M 9 The Autoionization of Water Pure water ionizes very slightly . The concentration of the ionized water is less than one-millionth molar at room temperature. 10 The Autoionization of Water We can write the autoionization of water as a dissociation reaction similar to those previously done in this chapter. Because the activity of pure water is 1, the equilibrium constant for this reaction is: [ ][ ] = OH O H K + 3 c H 2 O + H 2 O H 3 O + + OH- 11 The Autoionization of Water Experimental measurements have determined that the concentration of each ion is 1.0 x 10-7 M at 25 o C. We can determine the value of K c from this information. 12 The Autoionization of Water [ ][ ] ( )( ) 14 c 7- 7- c + 3 c x10 1.0 K 10 x 1.0 10 x 1.0 K OH O H K = = = 13 The Autoionization of Water This particular equilibrium constant is called the ion-product for water and given the symbol K w . [ ][ ] 14 + 3 w x10 1.0 OH O H K = = 14 The Autoionization of Water Example 18-3: Calculate the concentrations of H 3 O + and OH- in 0.050 M HNO 3 . HNO 3 + H 2 O H 3 O + + NO 3- 0.050 M 0.050 M 0.050 M 15 The Autoionization of Water Use the [H 3 O + ] and K w to determine the [OH- ]. [ ][ ] [ ] [ ] + 3 14 14 + 3 O H 10 . 1 OH 10 . 1 OH O H = = 16 The Autoionization of Water [ ] [ ] [ ] M 10 . 2 OH 10 . 5 10 . 1 O H 10 . 1 OH 13 2 14 + 3 14 = = = 17 The Autoionization of Water When HCl is added to water, the increase in [H 3 O + ] from HCl shifts the equilibrium and decreases the...
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Chap 18 - 1 18 Ionic Equilibria: Acids and Bases 2 A Review...

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