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Chapter 15

Chapter 15. Applying equilibrium. Titration Curves. Strong acid with strong Base Equivalence at pH 7. 7. pH. mL of Base added. Weak acid with strong Base Equivalence at pH >7. >7. pH. mL of Base added. Strong base with strong acid Equivalence at pH 7. 7. pH. mL of Base added.

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Chapter 15

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  1. Chapter 15 Applying equilibrium

  2. Titration Curves

  3. Strong acid with strong Base • Equivalence at pH 7 7 pH mL of Base added

  4. Weak acid with strong Base • Equivalence at pH >7 >7 pH mL of Base added

  5. Strong base with strong acid • Equivalence at pH 7 7 pH mL of Base added

  6. Weak base with strong acid • Equivalence at pH <7 <7 pH mL of Base added

  7. Summary • Strong acid and base just stoichiometry. • Determine Ka, use for 0 mL base • Weak acid before equivalence point • Stoichiometry first • Then Henderson-Hasselbach • Weak acid at equivalence point Kb • Weak base after equivalence - leftover strong base.

  8. Summary • Determine Ka, use for 0 mL acid. • Weak base before equivalence point. • Stoichiometry first • Then Henderson-Hasselbach • Weak base at equivalence point Ka. • Weak base after equivalence - leftover strong acid.

  9. Indicators • Weak acids that change color when they become bases. • weak acid written HIn • Weak base • HIn H+ + In- clear red • Equilibrium is controlled by pH • End point - when the indicator changes color.

  10. Indicators • Since it is an equilibrium the color change is gradual. • It is noticeable when the ratio of [In-]/[HI] or [HI]/[In-] is 1/10 • Since the Indicator is a weak acid, it has a Ka. • pH=pKa +log([In-]/[HI]) = pKa +log(1/10) • pH=pKa - 1 on the way up

  11. Indicators • pH=pKa + log([HI]/[In-]) = pKa + log(10) • pH=pKa +1 on the way down • Choose the indicator with a pKa 1 less than the pH at equivalence point if you are titrating with base. • Choose the indicator with a pKa 1 greater than the pH at equivalence point if you are titrating with acid.

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