topics 1.h + 2.acids and bases 3.definition of ph 4.reversible reactions, equilibrium, mas action...

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Topics 1. H + 2. Acids and Bases 3. Definition of pH 4. Reversible reactions, equilibrium, mas action 5. HendersonpHasselbalch equation 6. Buffers. Buffer capacity

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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+]

Rutherford-Thompson atom: Dimensions

m10-10 (ร…)10-15(Fermi)

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

๐‘๐ป=โˆ’ ๐‘™๐‘œ๐‘”10ยฟpH

Reversible Reactions โ€“ Rate constants - Equilibrium

BA B + AK1

k-1

๐‘˜1 [๐ต๐ด ]=๐‘˜โˆ’ 1 ( [๐ต ] [ ๐ด ] )

Henderson-Hasselbalch equation

HCl H+ + Cl-K1

k-1

At equilibrium

๐‘˜1๐‘˜โˆ’ 1

=ยฟ

โˆ’๐‘™๐‘œ๐‘”ยฟ

๐‘˜1๐‘˜โˆ’ 1

=๐พ

๐‘๐ป=๐‘๐พ +๐‘™๐‘œ๐‘”[๐ถ๐‘™โˆ’]

[ ๐ป๐ถ๐‘™ ]

Buffers and Buffer capacity

๐›ฝ=๐‘‘๐‘›๐‘Ž

๐‘‘๐‘๐ป=2.3ยฟ

In a given pH, ฮฒ is a function of pH and buffer concentration

Bibliography

โ€ข Bockris, J.Oโ€™M 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

~๐œ‡๐‘– (1 )=๐œ‡๐‘–โ‘

โ‘๐‘œ (1 )+๐‘…๐‘‡๐‘™๐‘›๐‘๐‘– (1 )+๐‘ง ๐‘–๐น โˆ… (1)

R= 8.3 J mol-1 K-1

โŒŠ~๐œ‡๐‘– โŒ‹= ๐ฝ ๐‘š๐‘œ๐‘™โˆ’1

๐น=๐‘ ๐ด๐‘’โˆ’=1,6022ร—104ร—6.03ร—1023

๐น=9.6485ร—104๐‘๐‘œ๐‘ข๐‘™๐‘š๐‘œ๐‘™โˆ’ 1

~๐œ‡๐‘– (2 )=๐œ‡๐‘–โ‘

โ‘๐‘œ (2 )+๐‘…๐‘‡๐‘™๐‘›๐‘ ๐‘– (2 )+๐‘ง๐‘– ๐นโˆ… (2)

โˆ†~๐œ‡๐‘–=๐‘…๐‘‡๐‘™๐‘›๐‘ ๐‘– (1 )๐‘ ๐‘– (2 ) ๐‘–

+๐‘ง๐‘– ๐น (โˆ… (1)โˆ’  โˆ… (2))

Thermal energy โ€“ microscopic view

Thermal energyBezanilla simulation

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

โˆ†โˆ…=โˆ’ ๐‘…๐‘‡๐‘ง๐‘– ๐น

ln๐‘๐‘– (1 )๐‘๐‘– (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+

๐‘‰๐‘ค๐‘Ž๐‘™๐‘™ /๐‘ ๐‘œ๐‘™๐‘ข๐‘ก๐‘–๐‘œ๐‘›=๐‘…๐‘‡๐น2.303 ๐‘™๐‘œ๐‘”ยฟ

๐‘‰ ๐ธ๐‘™๐‘’๐‘๐‘ก๐‘Ÿ๐‘œ๐‘‘๐‘’=๐‘‰ โ€ฒ+๐‘…๐‘‡๐น2.303 (๐‘๐ป )

BCECF