Unit 7

• Buffers Buffers are solutions that resist changes in pH when small amounts of acid or base are added. They consist of a weak acid and its conjugate base, or a weak base and its conjugate acid.
• Common Ion Effect

  When multiple compounds with a common ion are in solution, equilibrium is shifted and pH is affected
• Make up of Buffer Solutions

  Weak acid and its salt

  Weak base and its salt
• Henderson-Hasselbalch equation 


  $-log(Ka)+$$log([A]/[HA])$

  *use Kb for pOH of weak base

  Finds the pH of a weak acid (or pOH of a weak base) from its acid dissociation constant and log of the ration of the concentration of base to acid
• Solubility Constant 


  Ksp
• Steps to solve Acid/Base/Buffer Problems

  1) List major species

  2)Look for reactions that go to completion

  3)For reactions that can go to completion:

  -Determine concentrations of products

  -Write down major species after the reaction

  4)Look at each major component and decide if it is an acid or a base

  5)Pick the equilibrium constant that will control the pH. Use the Ka and Kb values to help decide the dominant equilibrium
• Adding a strong acid or base to a buffer solution

  The strong acid/base will completely ionize

  -Not ”ICE”! Use stoichiomety

  -Use the number of moles for each species present

  Use the ”BCA“ method for Moles

  Before, Change, After
• Optimum Buffers


  Hold a solution near a certain pH
• Finding desired pH for Optimum Buffers 


  Use Ka (for acid) or Kb (for base)

  Take $10^-pH$

  Can be explained by Henderson-Hasselbalch
• Titration of Strong Acid and Strong Base 


  *

  
• Titration of a Strong Base with Strong Acid


  *

  
• Titration of a Weak acid with a Strong Base


  *

  
• Titration of Weak base with a strong acid 


  *

  
• Titration of a polyprotic acid and strong base 


  *

  
• Equivalence point 


  #3

  
• Half-equivalence point 


  #2

  Point at which titration is halfway to the equivalence point