Lecture 6

Chemical Equlibria

Ca2+

(NH4)2C2O4

K+, Mg2+

K+. Mg2+

CaC2O4

precipitate

Filtration

Calcium separation

CaC2O4

Cu2+

KIO4

Fe3+, MnO4-

Cu2+

Spectrophotometricdetermination

Manganese determination

Fe3+, Mn2+

Requirements:

Yield 100% (± st.deviation of the method)

A convenient procedure

CaC2O4 can be isolated and weighed

Absorbance of MnO4- ion can be easily measured in visible light

99.99-100.01% for gravimetry (weighing) – 4 digits!99.9-100.1% for spectrometry (absorbance) – 3 digits!

Chemical Equilibria aA + bB cC+dD

ba

dc

BA

DCK

][][

][][

[A] Concentration related to standard state

Standard: Liquid or solid – pure liquid or solid

Gas -1 atm or 1 bar=105 Pa

Solution - 1 M

Le Chatelier PrincipleCa2+ + H2C2O4 CaC2O4 + 2H+

CO2 + H2O H+ + HCO3-

PbI2 Pb2+ + 2 I-

Pure solid ][

]][[

2

22

PbI

IPbK

22 ]][[ IPbKsp

Solubility Product

Common Ion effect: more common ion – less solubility

Pb2+ + 4 I- PbI42-

Complex (Ion) Formation

42

24

4 ]][[

][

IPb

PbI

Stability constant

More I- - higher solubility

O

H

H

H

H3O+ ion

More neighbors…

More neighbors…

OHHOH2

]][[ OHHKW

CH3 COH

OCH3 C

O-

O+ H+

Weak acid

element =OWeak conjugated base

51075.1][

]][[

HA

AHKa

HN

H

H+ H2O

HN+

H

H

H+ OH-

baseconjugated acid

][

]][[

3

4

NH

OHNHKb