Buffers
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Transcript of Buffers
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Weak Acids, Weak Bases
And Buffers
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Ionization/Dissociation of water
H2O + H2O H3O+ + OH-
H2O H+ + OH-
K=[H+] [OH-]
[H2O]K=1.8 x 10-16 M
[H+] [OH-] = 55.5 M x (1.8 x 10-16 M)[H+] [OH-] = 1 x 10-14 M2 (Kw)[OH-] = [H+] = 1 x 10-7 M
pH= -log10 [H+] = log
Log [H+] + log [OH-] = log 10-14
pH + pOH = 14
1H+
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Dissotiation of Weak Acids
CH3COOH CH3COO- + H+
(HA) (A-)
Henderson-Hasselbach Equation
[H+] = Ka[HA]
[A-]
pH = pKa + log[A-] Conjugated base
[HA] Acid
Ka = [H+] [A-]
[HA]
-log [H+] = -log Ka - log[HA]
[A-]
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CH3COOH CH3COO- + H+ Ka = 1.74 x 10-5
X2 = 1.74 x 10-5 [1-CH3COO-}
X = 1.74 x 10-5 x 1
pH = - logX = 2.38
Ka = 1.74 x 10-5 =[CH3COO-] [H+]
[CH3COOH]
[CH3COO-] [H+] = (1.74 x 10-5) [CH3COOH]X X 1-X
Calculating the pH of Weak Acid Solutions
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d % MW
NH3 0.91 25 15HCl 1.184 85 35.5H3PO4 1.7 85 98H2SO4 1.84 98 98CH3COOH 1.049 99.9 60
After Calculation:V1 N1 = V2 N2 or V1 C1 = V2 C2
can be used to prepare desired solution.
M =d x percentage x 1000
Molecular weight
! !
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The Mechanism of Buffer ActionKısmen dissosiye olmaları nedeniyle zayıf asitler ve onların konjuge baz formları proton verici ve proton alıcı olarak davranırlar:
CH3COOH CH3COO- + H+
NaOH Na+ + OH- H2O
By the same mechanism, weak bases can act as buffers.
CH3COOH CH3COO- + H+
HCl Cl- + H*
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0.5 1.0Ekivalent baz
pH
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pH of Body Fluids
Fluid pH
Blood 7.4Milk 6.6 – 6.9Urine (normal) 6.0Gastric juice 0.88Pancreatic secretions 8.0Intestinal secretions 7.7Erebrospinal fluid 7.4Saliva 7.2Tears 7.4
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Some weak acids or basesacid Conjugated base pK
H-COOH HCOO- + H+ 3.75
CH3-COOH CH3COO- + 4.76
CH3CHCOOH CH3CHCOO- + H+ 3.86
OH OH
H3PO4 H++H2PO4- H++HPO4= H+ PO4
3-
2.34 6.86 12.4
H2CO3 H+ + HCO3- CO3
2- + H+
3.8 10.2
C6H5OH C6H5O + H+ 9.89
N H4 NH3 + H+ 9.25 +
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Major Buffers
Acid form pKaCacodylic acid 6.2
BISTRIS 6.5
PIPES 6.8
İmidazole 7.0
HEPES 7.6
Tris 8.3
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Physiological Buffer Systems
1. Hemoglobin
2. Proteins
3. Phosphate buffer system
4. Carbonic acid / Bicarbonate system
Non-bicarbonatebuffers
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Carbonic acid-Bicarbonate Buffer system
H2CO3 H+ + HCO3- pK1 = 3.8
HCO3- H+ + CO3
2- pK2 = 10.2
CO2 + H2O H2CO3 H+ + HCO3-
CA
HCO3- / H2CO3 ratio is 20/1
pK’(apperent) = [HCO3
-] [H+]
H2CO3
= 6.1
7.4 = 6.1 + log [HCO3
-]
[H2CO3]
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Phosphate Buffer System
H2PO4- H+ + HPO4
2-
HPO42- / H2PO4 = 4/1
* Major intracellular inorganic buffer.
*H2PO4 excretion in urine is important for the regulation of blood pH.
pK = 6.8
7.4 = 6.8 + log HPO42-
H2PO4-
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Plasma Red blood cells
CO2
H2O
H2CO3
H+ + HCO3-
HCO3-
O2 release
Cl- Tis
su
e m
eta
bo
lism
CO2
O2
CO2 + H2O H2CO3
HCO3- + H+
Cl-
HHb
Carbamino Hb
H2PO4-
HPO4=
HbO2
O2
CA
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Plasma Red blood cells
CO2
H2O
H2CO3
H+ + HCO3-
HCO3-
O2 diffusion
Cl- Alv
eols
CO2
O2
CO2 + H2O H2CO3
HCO3- + H+
Cl-
HHb
Carbamino Hb
H2PO4-
HPO4=
HbO2
O2
CA