in Chemistry

Acids and Bases (2 of 2)

Part 1 of Acids and Bases is located here.

Dissociation Constant

At equilibrium, the rate of dissociation of the product AB is equal to the rate of associate of the reactant A and B

∴ at equilibrium:

Kd = [A] [B] / [AB]

Which is derived from an example such as: AB ↔ A + B @ Equilibrium

pH Indicators

pH indicators work because of the dissociation of the H+ ions in the indicator itself.

Common Indicators Range
Phenolphthalein 8 – 10
Methyl Red 4.5 – 6
Bromothymol 6 – 7.6


Buffer Solutions

Buffer solutions resist changes in pH.

buffer solution

The buffer solution absorbs the proton

Example:

HA + H2O ↔ H3O+ + A

Ka = [H3O+] [A] / [HA]

-log(Ka) = -log([H3O+] ([A] / [HA]))

-log(Ka) = -log([H3O+]) – log([A] / [HA])

pKa = pH – log([A] / [HA])

pH = pKa + log([A] / [HA])



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