Chem 211 - Titration Curve

Describe the titration curve of strong acid

At equivalence point, pH = 7

Describe a titration curve of weak acid

• pH is not 7 at equivalence point

• at half-equivalence point, pH = pKa

• larger Ka, smaller initial position

Write the Henderson Hasselbalch equation

pH = pKa + log [A-]/[HA]

What is a key characteristic of a titration with a weak diprotic acid?

Possesses 2+ equivalence points

What are some guidelines associated with weak diprotic acid titration

To see first endpoint: pKa2-pKa1 > 4

To see second endpoint Ka2 < 8

Equation for determining initial pH?

Equation for determining first equivalence point?

Equation for determining buffer region 1

pH = pKa1 + log [HA]/[H2A]

Equation for determining buffer region 2?

pH = pKa2 + log [A2-]/[HA]

Equation for determining endpoint 2?

Kb1 = K2/Ka2

Define what a buffer is

A mixture of a weak acid and its conjugate base that resists changes in pH in addition of small amounts of another acid or base

Provide an example of a buffer

Tricine, acetate buffer

Explain how you would prepare a buffer of a certain pH of which reagents and what amounts

Use HH equation and get the ratio of A-/HA

How do we choose an indicator?

pKa of indicator dye should be larger than pKa of weak acid