Chapter16_Piao - Chemistry: A Molecular Approach, 1st Ed....

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Chapter 16 Aqueous Ionic Equilibrium Chemistry: A Molecular Approach , 1 st Ed. Nivaldo Tro
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Tro, Chemistry: A Molecular Approach 2 Introduction
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Tro, Chemistry: A Molecular Approach 3
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Tro, Chemistry: A Molecular Approach 7
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Tro, Chemistry: A Molecular Approach 8 Common Ion Effect HA ( aq ) + H 2 O ( l ) A ( aq ) + H 3 O + ( aq ) adding a salt containing the anion, NaA, that is the conjugate base of the acid (the common ion) shifts the position of equilibrium to the left this causes the pH to be higher than the pH of the acid solution lowering the H 3 O + ion concentration
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Tro, Chemistry: A Molecular Approach 9 Common Ion Effect
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Tro, Chemistry: A Molecular Approach 13 Simplifying Calculating Buffer pH
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Tro, Chemistry: A Molecular Approach 16 Ex 16.1 - What is the pH of a buffer that is 0.100 M HC 2 H 3 O 2 and 0.100 M NaC 2 H 3 O 2 ? Write the reaction for the acid with water Construct an ICE table for the reaction Enter the initial concentrations – assuming the [H 3 O + ] from water is ≈ 0 HC 2 H 3 O 2 + H 2 O C 2 H 3 O 2 + H 3 O + [HA] [A - ] [H 3 O + ] initial 0.100 0.100 0 change equilibrium
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Tro, Chemistry: A Molecular Approach 17 [HA] [A - ] [H 3 O + ] initial 0.100 0.100 0 change equilibrium Ex 16.1 - What is the pH of a buffer that is 0.100 M HC 2 H 3 O 2 and 0.100 M NaC 2 H 3 O 2 ? represent the change in the concentrations in terms of x sum the columns to find the equilibrium concentrations in terms of x substitute into the equilibrium constant expression + x + x x 0.100 x 0.100 + x x        x x x K a 100 . 0 100 . 0 O H HC ] O H ][ O H [C 2 3 2 3 - 2 3 2 HC 2 H 3 O 2 + H 2 O C 2 H 3 O 2 + H 3 O +
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Tro, Chemistry: A Molecular Approach 18        x x x K a 100 . 0 100 . 0 O H HC ] O H ][ O H [C 2 3 2 3 - 2 3 2 determine the value of K a since K a is very small, approximate the [HA] eq = [HA] init and [A ] eq = [A ] init solve for x x 5 10 8 . 1 [HA] [A - ] [H 3 O + ] initial 0.100 0.100 0 change - x + x + x equilibrium x 0.100 x Ex 16.1 - What is the pH of a buffer that is 0.100 M HC 2 H 3 O 2 and 0.100 M NaC 2 H 3 O 2 ? 0.100 + x        100 . 0 100 . 0 O H ] O H O H 2 3 2 3 - 2 3 2 x K a K a for HC 2 H 3 O 2 = 1.8 x 10 -5
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Tro, Chemistry: A Molecular Approach 19 Ex 16.1 - What is the pH of a buffer that is 0.100 M HC 2 H 3 O 2 and 0.100 M NaC 2 H 3 O 2 ? K a for HC 2 H 3 O 2 = 1.8 x 10 -5 check if the approximation is valid by seeing if x < 5% of [HC 2 H 3 O 2 ] init % 5 % 018 . 0 % 100 10 00 . 1 8 . 1 1 5 the approximation is valid x = 1.8 x 10 -5 [HA] [A - ] [H 3 O + ] initial 0.100 0.100 0 change - x + x + x equilibrium 0.100 0.100 x
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Tro, Chemistry: A Molecular Approach 20 Ex 16.1 - What is the pH of a buffer that is 0.100 M HC 2 H 3 O 2 and 0.100 M NaC 2 H 3 O 2 ?
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This note was uploaded on 09/25/2010 for the course CHEM 123 taught by Professor Piao during the Spring '10 term at Aarhus Universitet.

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Chapter16_Piao - Chemistry: A Molecular Approach, 1st Ed....

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