lecture 6 chemical equlibria. ca 2+ (nh 4 ) 2 c 2 o 4 k +, mg 2+ k +. mg 2+ cac 2 o 4 precipitate...
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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