Titration Curves Chemistry 3202

Titration Curves A titration curve is a graph of changes in pH during a titration. The shape of the curve depends on the strengths of the acids and bases used in the titration. The endpoint occurs at the middle of the steep section of the curve

Endpoint pH = 7 Strong Acid with Strong Base acid is in the flask base is in the buret

Strong Base with Strong Acid pH = 7 Endpoint

pH < 7 Weak Base with Strong Acid Endpoint

Weak Acid with Strong Base pH > 7 Endpoint

SA with SB

WB with SA

SB with SA

WA with SB

WA with WB

1 st Endpoint 2 nd Endpoint Diprotic acid with SB

Indicators An indicator is a weak acid that changes color with changes in pH To choose an indicator for a titration, the pH of the endpoint must be within the pH range over which the indicator changes color

pH = 5.3 litmus methyl red chlorophenol red What color change for each indicator? → blue to red → red to yellow → yellow to red

Buffers A solution of a WA and its conjugate base, or a WB and its conjugate acid is called a buffer solution. eg. a solution with both CH 3 COOH (aq) and CH 3 COO - (aq)

Buffers The pH of a buffer solution changes slightly when moderate amounts acid or base are added. The buffer capacity is the amount of acid or base that can be added before considerable change in pH.

Buffers Write the equation to show what happens when: a) acid (H 3 O + ) & b) base (OH - ) is added to a CH 3 COOH (aq) /CH 3 COO - (aq) buffer.