19 Acid & Base Ionization Constants

19 Acid & Base Ionization Constants - At 50oC Kw = 5.48...

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1 1 At 50 o C K w = 5.48 x 10 -14 , what is the pH of pure water at this temperature? pH = - log [H 3 O + ] A) pH = 7.4 B) pH = 7.0 C) pH = 6.6 2 For pure water at 50 o C 2H 2 O H 3 O + + OH K w = [H 3 O + ] [OH - ] =5.48 x 10 -14 and the pH = 6.6 At this temperature, water is __________. A) acidic: [H 3 O + ] > [OH - ] B) neutral: [H 3 O + ] = [OH - ] C) basic: [H 3 O + ] < [OH - ] [H 3 O + ] = [OH - ] and pure water is neutral (has no net charge) at any temperature !
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2 3 Today’s To Do Explain why water can be neutral and have a pH different from 7.0. Write equilibrium constant expressions for acid ionization, K a , and base ionization, K b . Define pK a and pK b , and how they are related. Determine K a and K b values from the pH or pOH and other concentration information. Determine the pH and pOH from K a or K b values and other concentration information. Identify the relative strengths of acids and bases from pK a and pK b values. 4 Why and how do equilibrium constants depend on temperature? ln( ) ln( ) 1 ln( ) o o oo RT K G G K RT H S K R TR  
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3 5 Understanding the equation below mathematically. Reactants Products ln K > 0 then K > 1 and reaction as written is product favored! ln K < 0 then K < 1 and reaction is reactant favored! ln K = 0 then K = 1 and reactants and products are both present in comparable amounts 1 ln( ) oo H S K R TR  K e K ln 6 Which changes in enthapy and entropy produce a K > 1? H o < 0, an exothermic reaction S o > 0, entropy increases Enthalpy term becomes less important at higher temperatures.
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This note was uploaded on 03/29/2010 for the course CHE 132 taught by Professor Hanson during the Spring '08 term at SUNY Stony Brook.

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19 Acid & Base Ionization Constants - At 50oC Kw = 5.48...

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