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# L18 - Lecture 18 Basically Weak Weak Acids and Bases Key...

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Lecture 18 Basically Weak: Weak Acids and Bases Key Idea: The pH depends on the acid or base concentration and the degree of dissociation. NH 3 (aq) + H 2 O (l) ! NH 4 + (aq) + OH - (aq) HCOOH (aq) + H 2 O (l) ! H 3 O + (aq) + Cl - (aq) Acids are H+ donors Bases are H+ acceptors Brønsted-Lowry Theory Observe what water does in these equilibria! NH 4 + NH 3 OH - Water is an amphiprotic solvent: it can both accept and donate a proton 3 [ ][ ] w K H O OH + ! = 14 0 1.0 10 25 w K at C ! = " Autoionization of water 2 2 3 ( ) ( ) ( ) ( ) H O l H O l H O aq OH aq + ! + + ° ! At 25 o C : What is the pH of pure water? What is the pOH of pure water? 7.0 pH pOH = = However, at 50 o C : K w = 5.48 x 10 -14 6.6!! pH pOH = = At all temperatures, pure water has “neutral” pH!! Relationship between [H 3 O + ] and [OH - ] 14 1.0 x 10 0 1.0 x 10 -14 8 1.0 x 10 -6 1.0 x 10 -8 7 1.0 x 10 -7 1.0 x 10 -7 6 1.0 x 10 -8 1.0 x 10 -6 5 1.0 x 10 -9 1.0 x 10 -5 4 1.0 x 10 -10 1.0 x 10 -4 3 1.0 x 10 -11 1.0 x 10 -3 2 1.0 x 10 -12 1.0 x 10 -2 1 1.0 x 10 -13 1.0 x 10 -1 0 1.0 x 10 -14 1.0 x 10 0 pH OH - concentration H 3 O + concentration [H 3 O + ] [OH - ] = 10 -14 pH + pOH = 14 more acidic more basic

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Diluting Acids Can you turn an acid into a base by dilution?
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L18 - Lecture 18 Basically Weak Weak Acids and Bases Key...

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