Equilibrium principles in aqueous systems

Definitions and equations

solubility

amount of substance that will dissolve in a given amount of solvent

Ks definition

solubility product constant. a large Ks value means high solubility

PH to H₃O⁺

shift log - PH

H₃O⁺ to PH

-log H₃O⁺

H₃O⁺ to OH^-

1 × 10^-14 / H₃O⁺

OH^- to H₃O⁺

1 × 10^-14 / OH^-

OH^- to POH

-log OH^-

POH to OH^-

shift log - POH

POH to PH

14 - POH

PH to POH

14 - PH

Kw

1 × 10^-14

dilution factors equation

[new] = volume used / total volume x [original]

common ion effect

adding a common ion increases its concentration in the solution which shifts equilibrium to create more product reducing solubility

predicting precipitation

Q<Ks = no precipitate

Q=Ks = no precipitate

Q>Ks = precipitate

effect of acidic conditions on solubility

When put with a base H₃O⁺ neutralizes OH^- so [OH^-] decreases. equilibrium shifts to make more OH^- so solubility increases

effect of complex ions on solubility

if a complex ion can be formed ions will be removed from the solution to create a complex ion. So concentration o ion will decrease and equilibrium will shift to produce more of that ion increasing solubility

Ka

acid dissociation constant

Kb calculation

Kb = Kw/Ka

[OH^-] from Kb

[OH^-] = square root of Kb x [A^-]

conductivity of solutions

strong acid has increased conductivity due to it completely dissociating in water. This means that lots of charged ions are available making it a good electrolyte

Kc

equilibrium constant

Kc equation

products/reactants

Le chatelier’s principle

If you make a change to an equilibrium system the equilibrium will shift to minimize the change

Buffer solutions

Is made of a weak acid and its conjugate base or a weak base and it conjugate acid. It will resist changes in PH when small amounts of acid or base are added.

Henderson equation

PH = pKa + log [base]/[acid]

effectiveness of buffer solutions

PH<pKa more effective at overcoming addition of excess base

PH=pKa weak acid and conjugate base or weak base and conjugate acid are equal in concentration. the buffer is equally effective

PH>pKa more effective at overcoming addition of excess acid

equivalence point

equal amounts of acid and base. halfway up steepest point of curve

buffer zone

between initial point and equivalence point

indicators

show when equivalence point is reached. pKa of the indicator should be ± 1 between PH at the equivalence point

CO₃ ion

CO_3^2-

CrO₄ ion

CrO_4^2-

SO₄ ion

SO_4^2-

CO₃ ion

CO_3^2-

CIO₃ ion

CIO_{3 ^-}

NO₃ ion

NO_3^-

PO₄

PO_4^3-