  Water acts as both acid and base  Dissociates into H 3 O + and OH - ions  2H 2 O (l)  H 3 O + (aq) + OH - (aq)  Rewritten,  H 2 O (l) + H 2.

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  Water acts as both acid and base  Dissociates into H 3 O + and OH - ions  2H 2 O (l)  H 3 O + (aq) + OH - (aq)  Rewritten,  H 2 O (l) + H 2 O (l)  H 3 O + (aq) + OH - (aq) Water Dissociation

  Rate of reaction reaches equilibrium and allows [H 3 O + ] and [OH - ] to be determined  2H 2 O (l)  H 3 O + (aq) + OH - (aq)  K w = [H 3 O + ] [OH - ]  K w = water dissociation constant = 1x for pure water  [H 3 O + ] = 1x10 -7 M in pure water  [OH - ] = 1x10 -7 M in pure water Water Dissociation (cont.)

  K w = [H 3 O + ] [OH - ] = 1 x regardless of where ions come  More acid, increase [H 3 O + ] /decrease [OH - ]  2 sources for [H 3 O + ], so less water dissociation  More base, decrease [H 3 O + ] /increase [OH - ] Acid/Base Addition

  Measure of the concentration of [H 3 O + ] ions in an acidic/basic solution  Uses logarithmic scale  pH = -log[H + ] or –log[H 3 O + ]  [H 3 O + ] = 10 -pH  pOH = -log[OH - ]  pH + pOH = 14 pH

 pH Scale  Logarithmic scale.  Measures the concentration of hydrogen ions [H + ] in a solution.  Range from  NEUTRAL, pH=7. (pure water)  BASE, pH > 7. (ocean water, milk of magnesia, baking sodea)  ACID, pH < 7. (stomach acid/HCl, vinegar, soft drinks)

  Increase [H 3 O + ], decrease pH value, decrease [OH - ]  Decrease [H 3 O + ], increase pH value, increase [OH - ] pH scale (cont.)

 pH Scale

 How do we measure the pH of a solution?  Acid-base indicators  Weak acids/bases  (ex. litmus paper)  pH meter

 Equations  pH = -log[H + ]  pOH = -log[OH - ]  pH + pOH = 14  [H + ][OH - ] = 1x M 2

  What is the pH of Pepsi Cola if the [H 3 O + ] in the solution is M? Example 1

  Strong acids completely dissociate in solution  SOOO solution’s [H 3 O + ] ~ [H 3 O + ] in acid  All [H 3 O + ] ions resulting from acid pH and strong acids

  Find the pH of a 2.5M HCl solution. Example 2

  Find the pH of a 0.05M H 2 SO 4 solution Example 3

 1)[H 3 O + ] = 1x10 -7 M in water  not a big number 2)LeChatlier’s Principle  As more H 3 O + ions dissociate from water, reaction shifts to LEFT to compensate  If more H 3 O + ions added to solution, water reforms to try and compensate SOOO decrease in [H 3 O + ] from water dissociation Why is the [H 3 O + ] from water dissociation not a factor?

  Acid/Base Introduction Worksheet  pH calculation Problems Homework