Exact Acid & Base Treatment

Exact Acid& - Exact Treatment of Acid/Base Equilibria Chem 6BH Exact Acid Base Treatment Slide 1 Exact Treatment Preliminaries Pure water

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1 Exact Acid Base Treatment Slide 1 Exact Treatment of Acid/Base Equilibria Chem 6BH Exact Acid Base Treatment Slide 2 Exact Treatment: Preliminaries Pure water has [H 3 O + ] = [OH ] = 10 –7 and has been neglible when compared to amounts generated from acids or bases present in water. – What if we have very weak acids or bases? – What is we have very dilute solutions? An EXACT treatment of acid base equilibria is needed! Consider a weak acid HA with a concentration of c a Consider a weak acid A with a concentration of c b In solution we will have the following: H 3 O + , OH , HA, A , and M + (used to deliver A ) Need 5 independent equations to relate c a , c b , and K a to concs. of species present Both in same solution
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2 Exact Acid Base Treatment Slide 3 Exact Treatment: Equations Here are the equations we need to begin the exact solution: Eqn A: [ M + ] = c b (spectator ion with no effect) Eqn B: [ H 3 O + ][ OH ] = K W Eqn C: [ H 3 O + ][ A ] [ HA ] = K a Eqn D: c a + c b = [ HA ] + [ A ] (conservation of mass/material) Eqn E: [ M + ] + [ H 3 O + ] = [ OH ] + [ A ] (charge balance) NOTE: [ ] = conc at equilibrium Exact Acid Base Treatment Slide 4 Exact Treatment: The solution (1) 1. Get rid of M + : c a + c b = [ HA ] + [ A ]=[ HA ] + c b + [ H 3 O + ]–[ OH ] so
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This note was uploaded on 04/08/2008 for the course CHEM 6BH taught by Professor Hoeger during the Winter '08 term at UCSD.

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Exact Acid& - Exact Treatment of Acid/Base Equilibria Chem 6BH Exact Acid Base Treatment Slide 1 Exact Treatment Preliminaries Pure water

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