2. SURAH AL-FATIHAH

3. Buffers and weak acids
Buffers are solutions that resist change in pH when acid or base is added to it.
It consist of weak acid and its salt (acetic acid and sodium acetate )or a weak base and its salt (ammonium hydro oxide and ammonium chloride )

4. Mechanism of buffer action
Added H+ ions = in the form of strong acid ,combine with anions A-( largely form the salt component of buffer), to form the weakely dissociable HA, so that pH does become as acid as it would be in the absence of the buffer.

5. Mechanism cont.. Acetic acid freely ionizable
Sodium acetate to a large extent
CH3COOH=CH3COO+H+
CH3COONa=CH3COO +Na+
H Cl is added acetate will combine with H+ to form acetic acid and NaCl is formed

6. Mechanism contd..
When NaOH is added the H+ of the buffer (acetic acid) combine with OH- to form water ,which is weakely dissociated .
Thus pH change due to base addition is also prevented by buffer
OH+H+ =H2O

7. BUFFERING CAPACITY
The efficiency of a buffer in maintaining a constant pH on the addition of acid or base is referred to as buffering capacity.
The capacity to combine with added acid remains so long as there is supply of the buffer salt in the medium.
OH can be buffered as long as some of the acid HA remains to supply the H+.

8. H-H EQUATION
The quantitative relationship between the concentrate of weak (HA) and its conjugate (A-) is Henderson equation.
HA=weak acid =H+ +A-
H+ =proton

9. H-H EQUATION
Is important for under standing buffer action and acid –base balance in the blood and tissue.
Restating the expression for dissociation constant of an acid
The pH of a solution of a weak acid (or base) and its salt is given by
pH=pKa _log [HA/A-]

10. H-H EQUATION Ke =equilibrium constant K e =ionization constant
Or dissociation constant of an acid or Ka
Stronger acids :phosphoric acid, carbonic acid ,acetic acid have larger dissociation constant

11. Cont..
Weaker acids mono hydrogen PO4 have smaller dissociation constant
Pka=log 1/Ka
pKa =-logka
The stronger the tendency to dissociate a proton ,the stronger is the acid lower the pKa

12. H-H eq… Ka=[H+][A-]/HA First solve for [H+]=Ka [HA]/[A-]
Take neg log on both side log [H+]=-log Ka –log [HA]/A-
Putting values pH=pKa -log[HA]
pH=pKa+log[A-]/[HA]
pH=pKa

13. Determination of pH Take three test tubes
To one add 1ml sodium acetate+acetic acid=(log 1/10)=-1
10 ml both(log 10/10)=0
10ml Na acetate +1ml acid (log10/1)=1

14. Buffers of the body fluids
Intracellular buffers;phosphate buffers cossist of disodium hydrogen phosphate and sodium dihydrogen phosphate.
This has pka close to physiological ph
Pka=6.8

15. Contd. Protein buffers :depend on ionizable side chain
Histine imidazole group pka=6.1
16 histidine in albumin
38 histidine in haemoglobin

16. Buffers … Extracellular ;comprise43%(intracellular 57%)
65%=bicarbonate buffers
30%=haemoglobin
4%=protein
1%=phosphate buffers
Buffers are first line of defence against acid load

17. Bicarbonate buffer system
Consist of HCO3 and H2CO3
Most significant
65% of plasma buffering
40% of buffering of body
CO2 andHCO3 can diffuse easily across membranes
HCO3 (Metabolic component) regulated by kidney and co2 by respiration.

18. Buffers .. HCO3 22-26 mmol/lt (24mmol) Pka=6.1
H2CO3=(CO2 in forms dissolved)
pCO2=40
Solubility coeffeciant=0.3
pH=Pka+logHCO3/H2CO3
7.4=6.1+LOg24/1.2
7.4=6.1+LOg20
7.4=

19. Body buffers
Three mechanism: to regulate pH and acid base balance and maintain the blood pH (around 7.4)
1.blood buffers
2.respiratory mechanism
3.renal mechanism

20. EFFECTS OF ACID BASE DISTURBANCES
H+increased= acidosis,depression of C.N.S, Disorientation, death in coma.
H+decreased= alkalosis, overexcitability of C.N.S,convulsions.
First in peripheral Nerves than C.N.S
Sensory effects,Tingling(pins and needle sensation
Motor effects, muscle twitches, spasm
Extreme alkalosis- spasm of respiratory muscles, death

21. EFFECTS….. 2. CHANGES IN ENZYMES ACTIVITY
Altering shape and activity of protein molecule.
Some reactions are accelerated and some are depressed.

22. EFFECTS….. 3. CHANGES IN CELLULAR pH
Reduced contractility of actin and myosin in muscles.
CHANGES IN POTASSIUM LEVEL
H+ ions enters the cells for sodium and potassium.
H+ ions are eliminated more than potassium so hyperkalemia, cardic disfunction.

23. Blood buffers Bicarbonate buffer system: NaHCO/H2CO3
H2CO3 >H+ +HCO3
pH=pKa +log [salt]/[acid]
20:1 is the ratio
Alkali reserve : responsible for effective buffering of H+,generated in the body.

24. Blood buffers.
Bicarbonate buffers ;is index to understand the disturbances.
Phosphate buffers; this is important buffer intracellular .
Sodium di hydrogen phosphate and disodium hydrogen phosphate
Ratio of base to acid for phophate buffer is 4:1
Pk is 6.8

25. Tsunami disaster….

26. The end