topics 1.h + 2.acids and bases 3.definition of ph 4.reversible reactions, equilibrium, mas action...
TRANSCRIPT
Topics
1. H+
2. Acids and Bases3. Definition of pH4. Reversible reactions, equilibrium, mas action5. HendersonpHasselbalch equation6. Buffers. Buffer capacity
H+
Suppose chloride acid dissolved in water
HCl H+ + Cl-
The entity H+, hydrogen stripped from the electron, is simply a proton, without electronic cloud, with dimensions at least 4 orders smaller than a real atom. Its strong electrical field Impedes a free existence. What really happens, upon dissolution of HCl in water is:
HCl + H2O H3O+ + Cl-
H3O+ H2O + H+
HCl H++ Cl-
[H+]
Acids and Bases
Brรธnsted-Lewy Concept (1923)AcidHA H+ + A-
BaseB- + H+ BH
Arrhenius Concept (1890) AcidHA H+ + A-
BaseCOH C+ + OH-
Acid + base salt + water 2NaOH + H2SO4 Na2SO4 + 2H2O
Water has amphoteric character2H2O H3O- + H+
pH, reversible reaction, equilibrium, mass action
๐๐ป=โ ๐๐๐10ยฟpH
Reversible Reactions โ Rate constants - Equilibrium
BA B + AK1
k-1
๐1 [๐ต๐ด ]=๐โ 1 ( [๐ต ] [ ๐ด ] )
Henderson-Hasselbalch equation
HCl H+ + Cl-K1
k-1
At equilibrium
๐1๐โ 1
=ยฟ
โ๐๐๐ยฟ
๐1๐โ 1
=๐พ
๐๐ป=๐๐พ +๐๐๐[๐ถ๐โ]
[ ๐ป๐ถ๐ ]
Buffers and Buffer capacity
๐ฝ=๐๐๐
๐๐๐ป=2.3ยฟ
In a given pH, ฮฒ is a function of pH and buffer concentration
Bibliography
โข Bockris, J.OโM and Reddy, A.K.N.: Modern Electrochemistry. Plenum Press, 1970. Vol.1, 1970. Chap. 5. Protons in solution.
Questions
1. For a [H+] of 10-10M to 10-1M, in steps fo 10-3M, draw a plot of pH x [H+].
2. Consider 1 L of a solution of a buffer of pK=7.5 amd concentration of 10 mM. Starting with a buffer base concentration of 9,9 mM, add progressively a strong acid, in amounts of 0.05 mmol. At equilibrium draw the curve relating pH to the total amount of acid added. Where is the point of maximal buffering power?
3. Suppose a buffer if pK=7.0 in concentration of 5 mM. What are the concentrations of acid and base for buffering a solution at a pH of 6,0.
Medidas de pH
I. EletrรณdiosII. Indicadores fluorescentes
BibliografiaKoryta, J.: Ion-Selective Electrodes. 1974. Cambridge University Press.Vanysek, P.> The glass pH electrode.The Electrochemical Society Interface. 2004Lakowicz, J.R.: Principles of fluorescence spectroscopy. 2nd ed., 1999. Fluwer Academy/Plenum Press
Electrochemical potential of a solute in a phase โ Macroscopic view
Thermal energy T (K)
C1
1
C2
รธ2
M
C: concentration, mol/lร: Electrical potential, V
~๐๐ (1 )=๐๐โ
โ๐ (1 )+๐ ๐๐๐๐๐ (1 )+๐ง ๐๐น โ (1)
R= 8.3 J mol-1 K-1
โ~๐๐ โ= ๐ฝ ๐๐๐โ1
๐น=๐ ๐ด๐โ=1,6022ร104ร6.03ร1023
๐น=9.6485ร104๐๐๐ข๐๐๐๐โ 1
~๐๐ (2 )=๐๐โ
โ๐ (2 )+๐ ๐๐๐๐ ๐ (2 )+๐ง๐ ๐นโ (2)
โ~๐๐=๐ ๐๐๐๐ ๐ (1 )๐ ๐ (2 ) ๐
+๐ง๐ ๐น (โ (1)โ โ (2))
Campos elรฉtricos โ forรงas elรฉtricas
Forรงa elรฉtrica โ lei de Coulomb
q
WV
dx
dV
q
f
Campo elรฉtrico
Diferenรงa de potencial elรฉtrico
+-
+
-
221*
r
qqkf
Carga do e- 1,60*10-19 coul
Constante de Faraday
F=NA*e-=
96484 coul/mol
C1
1
C2
รธ2
M
Membrane (M) Properties
1. Impermeable membrane
2. Membrane permeable to solutes
=0
3. Membrane permeable to cations or to anions
=0
โโ =โ ๐ ๐๐ง๐ ๐น
ln๐๐ (1 )๐๐ (2 )
Ion Exchangers โ Glass Electrodes
-----
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H+
H+
H+
H+
H+
H+H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
๐๐ค๐๐๐ /๐ ๐๐๐ข๐ก๐๐๐=๐ ๐๐น2.303 ๐๐๐ยฟ
๐ ๐ธ๐๐๐๐ก๐๐๐๐=๐ โฒ+๐ ๐๐น2.303 (๐๐ป )