1. Acid-Base Titrations

2. Acid-Base Titrations • Add solution (either the acid or the base) from buret to solution in flask • The concentration of one solution is known. One concentration is unknown. • The goal is to find the equivalence point: the point at which stoichiometrically equivalent quantities of acid and base have been combined (moles of acid = moles of base).

3. Acid-Base Titrations Can use an indicator to signal the equivalence point. An indicator is a dye that changes colors within a certain pH range. End point – point of indicator color change

4. Acid-Base Indicators

5. Acid-Base Indicators Can use an indicator to signal the equivalence point. An indicator is a dye that changes colors within a certain pH range. End point – point of indicator color change Must select an indicator with an end point approx. equal to the equivalence point of the acid-base reaction

6. Acid-Base Indicators • Usually a weak acid. Can be a weak base. • Shows distinctly different colors in non-ionized and ionized forms: HIn H+ + In- acid form base form

7. Acid-Base Indicators HIn H+ + In- acid form base form In acid: H+ concentration high equilibrium shift to left color of HIn In base: OH- consumed H+ equilibrium shifts to right color of In-

8. Acid-Base Titrations Can use pH meter and plot a titration curve. The equivalence point is the most vertical part of the curve.

9. Generic Titration Curve

10. Acid-Base Titrations We will look at three kinds of titrations: • Strong acid by a strong base • Weak acid by a strong base • Weak base with a strong acid

11. Acid-Base Titrations For each type, we will learn to write reactions for and calculate pH at four different points in the titration: • The initial pH before any titrant is added • At any point between the initial pH and the equivalence point • At the equivalence point • After the equivalence point

12. Strong Acid – Strong Base Titration • Describe a strong acid in solution. • What happens between a strong acid and a strong base? • At the equivalence point, what is true? • What happens after that? (What do you have present in solution after that?)

13. Weak Acid – Strong Base Titration • Describe a weak acid in solution. • What happens between a weak acid and a strong base? • At the equivalence point, what is true? • What happens after that? (What do you have present in solution after that?)

14. Weak Base – Strong Acid Titration • Describe a weak base in solution. • What happens between a weak base and a strong acid? • At the equivalence point, what is true? • What happens after that? (What do you have present in solution after that?)