Aqueous Solutions and ph by wuxiangyu

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									Aqueous Solutions and pH
        Hydronium Ions and Hydroxide Ions


   Acids produce the hydronium (H3O+) ion in water:
       HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq)

   Bases produce the hydroxide ion (OH-) in water:
       NaOH(aq)  Na+(aq) + OH-(aq)
             Self-Ionization of Water

   Water produces both hydronium and hydroxide ions through self-
    ionization:
                  H2O(l) + H2O(l)  H3O+(aq) + OH-(aq)
    (Brackets [ … ] are used to symbolize concentration in molarity)

                      Kw = ionization constant of water

                              Kw = [H3O+] [OH-]
                             (Kw = 1 x 10-14 M2)
         [H3O+] = 1 x 10-7M               [OH-] = 1 x 10-7M
                        pH Scale
- A means of expressing acidity or basicity of a solution.




           http://www.mpcfaculty.net/mark_bishop/pH_range.jpg
                           pH

   Expressing acidity or basicity in terms of H3O+ or OH-
    concentration can be difficult due to extremely small
    values.
   pH is a more convenient means of quantitatively
    describing acidity of a solution.
   pH stands for “pouvoir hydrogene” – power of
    hydrogen.
             pH Calculations

              pH = -log[H3O+]

The logarithm (log) of a number is equal to the power
that 10 must be raised to equal the number.

           Example:      log (1 x 10-7) = -7
                       pH Practice

1) What is the pH of a solution with a [H3O+] = 1.0 x 10-7?
                pH = -log(1 x 10-7)
                     pH = -(-7.0)
                        = 7.0
2) What is the pH of a solution with a [H3O+] = 3.21 x 10-4?

              pH = -log (3.21 x 10-4)
                    pH = - (-3.49)
                       = 3.49
      pOH Calculations & Practice

                   pOH = -log[OH-]
1) What is the pOH of a solution with a [OH-] = 1.0 x 10-9?
                 pOH = -log(1 x 10-9)
                     pOH = -(-9.0)
                        = 9.0
2) What is the pOH of a solution with a [OH-] = 6.74 x 10-8?
               pOH = -log (6.74 x 10-8)
                  pOH = - (-7.17)
                       = 7.17
Calculating Concentrations from pH & pOH

      [H3O+] = 10-pH              [OH-] = 10-pOH

1) What is the [H3O+] of a solution with a pH = 12.3?
                [H3O+] = 10-12.3
            [H3O+] = 5.01x10-13M
2) What is the [OH-] of a solution with a pOH = 4.25?
                  [OH-] = 10-4.25
             [OH-] = 5.62x10-5M
Connection between hydronium & hydroxide


              pH + pOH = 14

           [H3O+] [OH-] = 1 x 10-14

  Neutral solutions:
                 [H3O+] = [OH-] & pH = 7
  Acidic solutions:
                 [H3O+] > [OH-] & pH < 7
  Basic solutions:
                 [H3O+] < [OH-] & pH > 7
Summary of Equations

    pH = -log[H3O+]
   pOH = -log[OH-]

     [H3O+] = 10-pH
     [OH-] = 10-pOH

   pH + pOH = 14
 [H3O+] [OH-] = 1 x 10-14
             Practice Chart

 [H3O+]       [OH-]       pH     pOH

6.7 x 10-4

                          3.17

                                 12.2

             2.5 x 10-8
   Calculator Help

If you have a TI-30Xa such as the one
shown, you must enter the information in
the formula backwards.
For example:
What is the pH of a solution with a [H3O+] = 3.21 x 10-4?
               3   2           1

       pH = - log (3.21 x 10-4)

   1) Enter 3.21EE-4
   2) Press “log”
   3) Press +/- key
Calculator Help cont.

What is the [H3O+] of a solution with a pH = 12.3?
                         3   2 1

             [H3O+] = 10 -12.3

         1) Enter 12.3
         2) Press +/- key
         3) Press 10x key
Graphing and 2-line calculators

Enter exactly as formula reads!

								
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