_mol_L_ 2 - wbm-chemistry by hcj

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									Acid-Base Titration and pH

         Chapter 16
Self-Ionization of water
   Two water molecules produce a
    hydronium ion and a hydroxide ion by
    transfer of a proton




                  chemistry chapter 16     2
Pure water
   Concentrations of hydronium and
    hydroxide ions of 1.0 x 10-7 mol/L at
    25 °C.




                   chemistry chapter 16     3
Expressing concentrations
   Brackets indicate concentration in mol/L
   [H3O+] means
       Hydronium ion concentration in moles per
        liter
            or
       Molar hydronium ion concentration



                     chemistry chapter 16          4
Ionization constant of water

            
     K w  H 3O OH  
                                       
                                             
   1.0 x 10-14 M2   or (mol/L)2
   Constant over ordinary room
    temperatures
   For pure water or dilute aqueous
    solutions
                  chemistry chapter 16           5
Solutions
   Neutral
       [H3O+]=[OH-]
   Acidic
       [H3O+]>[OH-]
   Basic
       [H3O+]<[OH-]



                       chemistry chapter 16   6
Strong bases
   Ionize completely in solution
   Molar concentration of hydroxide ions is
    the same as the molarity of the solution
    times the subscript of hydroxide.
   Example: A 1.0 x 10-3 M LiOH solution
    has [OH-] of 1.0 x 10-3 M
   Example: A 1.0 x 10-3 M Ca(OH)2
    solution has [OH-] of 2.0 x 10-3 M

                  chemistry chapter 16     7
Strong Acids
   Ionize completely in solution
   Molar concentration of hydronium ions is the
    same as the molarity of the solution times the
    subscript of hydrogen.
   Example: A 1.0 x 10-4 M HCl solution has
    [H3O+] of 1.0 x 10-4 M
   Example: A 1.0 x 10-4 M H2SO4 solution has
    [H3O+] of 2.0 x 10-4 M

                    chemistry chapter 16         8
Using Kw
   If you know the concentration of
    hydronium or hydroxide ions, you can
    use Kw to find the concentration of the
    other ion.
   See page 484

                 
           K w  H 3O OH    
                                          
                                                
                     chemistry chapter 16           9
pH
   The negative of the common logarithm
    of the hydronium ion concentration


                      
        pH   log H 3O            
                                        

                 chemistry chapter 16       10
pOH
   The negative of the common logarithm
    of the hydroxide ion concentration


        pOH   log OH             
                                        

                 chemistry chapter 16       11
relationship
     pH  pOH  14.0




               chemistry chapter 16   12
chemistry chapter 16   13
Discuss
   What is the concentration of hydronium and
    hydroxide ions in pure water at
    25 °C?
   For each of the following properties, is the
    solution acidic or basic?
        [H3O+] = 1.0 x 10-3 M
       [OH-] = 1.0 x 10-4 M
       pH = 5.0
       pH = 8.0

                        chemistry chapter 16       14
Acid-Base indicators
   Used to obtain an approximate value for
    pH.
   Compounds whose colors are sensitive
    to pH.
       Weak acids or weak bases




                     chemistry chapter 16   15
Transition interval
   The pH range over which an indicator
    changes color
   See page 495




                  chemistry chapter 16     16
Universal indicators
   Use a combination of several different
    indicators.
   pH paper has been soaked in a
    universal indicator.




                  chemistry chapter 16       17
pH meters
   Used to find the exact pH
   Measures the voltage between two
    electrodes placed in solution.
       Changes with hydronium ion concentration




                     chemistry chapter 16      18
Titration
   The controlled addition and
    measurement of the amount of a
    solution of known concentration
    required to react completely with a
    measured amount of a solution of
    unknown concentration.



                  chemistry chapter 16    19
Equivalence point
   When the two solutions used in a
    titration are present in chemically
    equivalent amounts
       Not always neutral




                     chemistry chapter 16   20
End point
   The point in a titration at which an
    indicator changes color.
   Can be used to find equivalence point.
       If the indicator changes color at the
        equivalence point




                      chemistry chapter 16      21
Strong acid titrated with
strong base




            chemistry chapter 16   22
Weak acid titrated with strong
base




            chemistry chapter 16   23
Discuss
   P. 503 section review 1 and 2.




                  chemistry chapter 16   24
Standard solution
   The “known” solution
   Its concentration is known precisely




                  chemistry chapter 16     25
Primary standard
   Highly purified solid compound
   Used to check the concentration of the
    known solution




                  chemistry chapter 16       26
Titration process
   See pages 500 - 501




                 chemistry chapter 16   27
Calculating the unknown
concentration
1.   Write the balanced chemical equation.
2.   Determine the moles of the known
     solute.
3.   Determine the moles of the unknown
     solute.
4.   Determine the molarity of the
     unknown solution.

                 chemistry chapter 16    28
Example
   A 25.00 mL sample of a solution of
    RbOH is neutralized by 19.22 mL of a
    1.017 M solution of HBr. What is the
    molarity of the RbOH solution?
   0.7820 M




                  chemistry chapter 16     29
You try
   If 29.96 mL of a solution of Ba(OH)2
    requires 16.08 mL of a 2.303 M solution
    of HNO3 for complete titration, what is
    the molarity of the Ba(OH)2 solution?
   0.6182 M




                  chemistry chapter 16    30
You try
   You have a 0.83 M vinegar solution.
    You are going to titrate 20.00 mL of it
    with a 0.519 M NaOH solution. At what
    volume of added NaOH solution would
    you expect to see an end point?
   37 mL


                  chemistry chapter 16    31

								
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