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20.1. “I pity the fool who does not know how to do pH calculations!”. Hydrogen Ions and Acidity. Self-ionization - the reaction in which two water molecules produce ions. H 2 O --> H + + OH - Water Hydrogen ion hydroxide ion.

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20.1

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  1. 20.1 “I pity the fool who does not know how to do pH calculations!” Hydrogen Ions and Acidity

  2. Self-ionization - the reaction in which two water molecules produce ions H2O --> H+ + OH- Water Hydrogen ion hydroxide ion H2O + H2O --> H30+ + OH- Water Water Hydronium ion hydroxide ion Pure Water: neutral solution [H30+] = 1.0 x 10-7 M [OH-] = 1.0 x 10-7 M Kw = ion-product constant for water Kw = [H30+] [OH-] = 1.0 x 10-14 M

  3. Remember LeChatelier?? What happens to the H+ concentration when the OH- concentration increases? H2O <--> H+ + OH- Acidic: when [H+] is greater than [OH-] Basic: when [OH-] is greater than [H+] AKA: Alkaline solution

  4. Use the Kw expression to solve the following: Kw = [H30+] [OH-] = 1.0 x 10-14 M 1. What is [H30+] equal to if [OH-] is 1.9 x10-2 M? 2. What is the hydroxide concentration if the hydronium concentration is 5.1 x10-9 M?

  5. pH: scale used to measure how acidic or basic a solution is pH = - log [H30+] Acid: pH < 7.0 [H30+] > 1 x 10-7 Neutral: pH = 7.0 [H30+] = 1 x 10-7 Base: pH > 7.0 [H30+] < 1 x 10-7

  6. Equations for all pH and related problems... pH = - log [H30+] pOH = - log [OH-] [H30+] = inv log (-pH) [OH-] = inv log (-pOH) pH + pOH = 14 [H30+] [OH-] = 1.0 x 10-14 M

  7. Complete the following table using the equations on the previous slide:

  8. Acid / Base Indicators HIn <--> H+ + In- acid form base form Use LeChatelier to determine which direction the reaction will shift... More [H+]…reaction shifts __________ Less [H+]…reaction shifts __________

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