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Water

pH. Water. Water is in equilibrium with its ions H 2 O(l)  H + (aq) + OH - (aq) K w = [H + ][OH - ] K w = 1.0 x 10 -14 at 25 °C In neutral solutions [H + ]=[OH - ]= 1x10 -7 If [H + ]>[OH - ], solution is acidic If [H + ]<[OH - ], solution is basic. Example.

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Water

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  1. pH

  2. Water • Water is in equilibrium with its ions H2O(l)  H+(aq) + OH-(aq) Kw = [H+][OH-] • Kw = 1.0 x 10-14 at 25°C • In neutral solutions [H+]=[OH-]= 1x10-7 • If [H+]>[OH-], solution is acidic • If [H+]<[OH-], solution is basic

  3. Example • Find the [H+] if a) [OH-]= .010M b) [OH-]= 2.0 x 10-9 M

  4. pH • Very small numbers can be conveniently expressed on a log scale • pH = -log [H+] • pH = 7, neutral • pH < 7, acidic • pH > 7, basic

  5. Example • Calculate the pH of lemon juice with an [H+]= 3.8 x 10-4M • Calculate the pH of window cleaner with an [H+]= 5.3 x 10-9M • What is the [H+] of apple juice with a pH of 3.76.

  6. pOH • pOH = -log [OH-] • pOH = 7, neutral • pOH < 7, basic • pOH > 7, acidic • pH + pOH = 14.00

  7. Indicators • Used to estimate pH • Colored substance that exists in either acid or base form • Acid and base form are different colors • By knowing the pH where it changes color, we can determine its relative pH

  8. Strong Acids and Bases • Strong acids and bases ionize completely in solution • Strong acids: HCl, HBr, HI, HNO3, HClO4, H2SO4 (only the 1st H) • Strong bases: hydroxides of group I and II, except Be

  9. .10M HNO3 .10M H+ • .75M H2SO4  .75M H+ • .50M NaOH  .50M OH- • .75M Ca(OH)2  1.5M OH-

  10. Example • What is the pH of a solution of a) .010M HCl b) .010M Ca(OH)2

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