Acid Dissociation Constant, pH curves,

What is Ka

The equilibrium constant for weak acids and bases

Ka equation

Ka = [H+] [A-]/ [HA]

Ka = [H+]² / [HA]

methyl orange:

colour at low pH

colour at high pH

range

colour at low pH - red

colour at high pH - yellow

range → 3.1 - 4.4

Phenolphthalein:

colour at low pH - colourless

colour at high pH - pink

range → 8.3 - 10

colour at low pH

colour at high pH

range

What is a buffer?

A buffer is a solution that resists changes in pH when small amount of acid or alkali are added.

What do acidic buffers contain?

A weak acid and the salt of that weak acid

What do basic buffers contain?

A weak base and the salt of that weak base

How do acidic buffers resist an acid?

Excess H+ reacts with the negative ion, shifting equilibrium to the left, decreasing concentration of H+

How do acidic buffers resist an base?

The excess OH- reacts with the H+ to make water 

How do basic buffers resist an acid?

The excess H+ will react with the OH- to make water. The increase in water forces the equilibrium to shift to the right to replace the OH- ions that were used up.

How do basic buffers resist a base?

The extra OH- ions react with the positive ion to shift the equilibrium to the left to form the reactants again.