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Unformatted text preview: Chapter 16 Homework – Sections 16.7 to 16.10 Red concepts: 16.5,16.8 Red exercises: 16.75, 16.77, 16.79, 16.81, 16.83 16.87, 16.93, 16.95, 16.97, 16.107, 16.110, 16.117, 16.120 Weak Bases Many bases only partially react with water: B( aq ) + H 2 O( l ) ↔ HB + ( aq ) + OH ( aq ) The base dissociation constant, K b , describes the extent of protonated and deprotonated species at equilibrium: Larger values of K b indicate stronger bases (more OH generated). K b = 1.8x105 K b = 1.8x104 Calculating pH from K b 1) Make a table with the known information. 2) Write the changes in concentrations as a function of an unknown variable (e.g., “x”). 3) Calculate the equilibrium concentrations as a function of x. 4) Write an algebraic expression for K b as a function of x. 5) Find the value of x. 6) Calculate the equilibrium concentrations. 7) Calculate pH from [OH ]. 1) Make a table with the known information. BrO (M) BrOH (M) OH (M) initial 1.15 0 0 change final Example: 1.15 M BrO with K b = 4.0 x 106 BrO + H 2 O ↔ BrOH + OH 2) Write the changes in concentrations as a function of an unknown variable (e.g., “x”). BrO (M) BrOH (M) OH (M) initial 1.15 0 0 change x x x final 3) Calculate the equilibrium concentrations as a function of x. BrO (M) BrOH (M) OH (M) initial 1.15 0 0 change x x x final 1.15  x x x 4) Write an algebraic expression for K b as a function of x. BrO (M) BrOH (M) OH (M) initial 1.15 0 0 change x x x final 1.15  x x x 5) Find the value of x. 6) Calculate the equilibrium concentrations. BrO (M) BrOH (M) OH (M) initial 1.15 0 0 change 2.1x103 2.1x103 2.1x103 final 1.15 2.1x103 2.1x103 7) Calculate pH from [OH ]. BrO (M) BrOH (M) OH (M) initial 1.15 0 0 change 2.1x103 2.1x103 2.1x103 final 1.15 2.1x103 2.1x103 Calculating K b from pH 1) Make a table with the known information....
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This note was uploaded on 09/13/2011 for the course CHEM 102 taught by Professor Todd during the Spring '08 term at UNC.
 Spring '08
 Todd
 Chemistry, Bases

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