Acids and Bases 3

Chapter 18

Characteristics of a good buffer

1. should control pH at intended value

2. buffer capacity

3. typical concentrations are 0.1M - 1M

Purpose of Buffer

the change in pH when acid or base is added to the solution is minimized (but there is still a change)

Strong Acid / Strong Base Reactions results

• complete neutralization (large K)

• all that’s left over is a pH neutral salt

• gives us equal molar amounts at the equivalence point

• favor direction where stronger acid and base react to form a weaker acid and base

Common Ion Effect

when more of the common ion is added (a product), the equilibrium will shift left to reduce disturbance. This results in a reduction of the other product (ie OH) which in that case lowers the pH

Acid Base Titration

placing one reactant with a known concentration in a buret and adding another substance of unknown concentration to it

Titrant

Substance being added during titration

Equivalence point

moles of acid - moles of base

Endpoint

point at which indicator changes color

How to choose an indicator

endpoint is as close to equivalence point as possible

titration curve

plot of pH vs Volume of added titrant