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pH Scale

pH Scale. Determines concentration (strength) of an acid or base. Acids below 7 Bases above 7. [http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter15/Text_Images/FG15_03.JPG]. pH Scale. Indicators show the pH level in the lab.

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pH Scale

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  1. pH Scale • Determines concentration (strength) of an acid or base. • Acids below 7 • Bases above 7 [http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter15/Text_Images/FG15_03.JPG]

  2. pH Scale • Indicators show the pH level in the lab. [http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter15/Text_Images/FG15_05.JPG]

  3. Click for indicator demo [http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH15/FG15_13.JPG]

  4. pH Scale • pH is based on the concentration of the hydronium ion. [http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH15/FG15_00-02.JPG]

  5. pH Scale pH is not a linear scale!! pH = -log[H3O+] [http://wps.prenhall.com/wps/media/objects/476/488316/Instructor_Resources/Chapter_14/FG14_15.JPG]

  6. pH Scale • Example: If the concentration of hydronium ions is 3.0 x 10-4M, what is the pH? • pH = -log[3.0 x 10-4] • pH = 3.5

  7. pH Scale • What about changing pH to[H3O+] • [H3O+]=10-pH • Example: If the pH of a base is 12.5, what is [H3O+]?

  8. pH Scale • [H3O+] = 10-12.5 • 3.16 x 10-13M • But wait…doesn’t a base give off OH-???

  9. Water as an Acid & Base [http://wps.prenhall.com/wps/media/objects/476/488316/Instructor_Resources/Chapter_14/FG14_14-01un.JPG]

  10. Water as an Acid & Base • Keq = [H3O+][OH-] • Water is neutral so pH = 7…. [http://wps.prenhall.com/wps/media/objects/476/488316/Instructor_Resources/Chapter_14/FG14_14-02un.JPG]

  11. Water as an Acid & Base • [H3O+] = 1 x 10-7 • Also, [H3O+] and [OH-] are equal since water is neutral [http://wps.prenhall.com/wps/media/objects/476/488316/Instructor_Resources/Chapter_14/FG14_14-02un.JPG]

  12. Water as an Acid & Base • 1 x 10-14 = [H3O+][OH-] • This is known as Kw. • (Equilibrium Water Constant) [http://wps.prenhall.com/wps/media/objects/476/488316/Instructor_Resources/Chapter_14/FG14_14-02un.JPG]

  13. pOH scale • When NH3 is dissolved in water, it gives off the Hydroxide Ion (OH-) [http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH15/FG15_00-04.JPG]

  14. pOH Scale • pOH scale is reversed • (0-7 are bases, 7-14 acids) • pOH = -log[OH-] • [OH-]=10-pOH

  15. pH & pOH • pH + pOH = 14 • Example: • If [OH-] for a base is 2.00 x 10-2 M, what is the pH?

  16. pH & pOH • pOH = -log[2.00 x 10-2] • pOH = 1.70 • pH + 1.70 = 14 • pH = 12.3

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