University:
Mt. San Antonio College
Course:
CHEM 20 | Biochemistry
Academic year:

2024
Views:

433

Pages:

1
Author:

Carlo M.

BIOCHEMISTRY LABORATORY MODULE 2 - BUFFER CAPACITY • BUFFER CAPACITY • • Also known as buffer efficiency, buffer index, buffer value Is the magnitude of resistance to pH changes MECHANISM OF BUFFER ACTION • • Strong acid are buffered by weak base Strong bases are buffered by weak acid BUFFER EQUATION / HENDERSON HASSELBALCH EQUATION • • • • Weak acid and its salt o pH = pKa + log [salt]/[acid] Weak base and its salt o pH = pKw - pKb + log [salt]/[acid] o pKw =14 Examples o What is the pH of a buffer solution with 0.05 M sodium borate and 0.005 M boric acid? The pKa value of boric acid is 9.24 at 25°C. o What is the pH of a buffer solution prepared with 0.05 M ammonia and 0.05 M ammonium chloride. The Kb value of ammonia is 1.80 × 10–5 at 25°C. Practice o What is the pH of the buffer prepared with 0.51M disodium phosphate and 1.1M sodium acid phosphate? Its pka value is 7.21. o Compute for the pH of a buffer containing 0.62M boric acid (ka= 5.9 x10-10 M) and 0.45M sodium borate. FACTORS INFLUENCING THE pH OF BUFFER SOLUTION • • • Addition of neutral salts to buffer o Sodium Chloride, Ammonium sulfate and Magnesium Sulfate Dilution/ addition of water Temperature o Acetate Buffers - pH increase with temp, o Boric Acid - Sodium Borate Buffers - pH decrease with temp NOTES • • Altering ionic strength: Sodium Chloride, Ammonium sulfate and Magnesium Sulfate, because they are free charge they can influence an increase in the number of H or OH May cause a small postive and negative diviation bec it alter activity coefficient. WATER IT SELF CAN ACT AS WEAK ACID AND WEAK BASE BIOLOGICAL BUFFER SYSTEM • • Major intracellular buffer o Dihydrogen phosphate- monohydrogen phosphate conjugate acid-base pair. ▪ Hemoglobin ▪ Proteins Major extra cellular buffer o Carbonic acid –bicarbonate conjugate acid-base pair o Buffer system that helps maintain the pH of the blood ▪ Serum Protein • ▪ Ammonia Blood is maintained at pH about 7.4 by the: o Primary Buffer ▪ Carbonic acid/ bicarbonate buffer system ▪ Acid/alkali sodium salts of phosphoric acid o Secondary Buffer ▪ Hemoglobin/oxyhemoglobin ▪ Acid/alkali potassium salts of phosphoric acid Other Biological Fluid o Lacrimal fluid ▪ pH about 7.4 with range 7-8 o Urine ▪ Average pH 6; 4.5 low and 7.8 high ▪ pH below normal value, hydrogen ion are excreted by the kidney ▪ pH above normal value, hydrogen ion are retained o o o This figure shows the major organs that help control the blood concentrations of CO2 and HCO3-, and thus help control the pH of the blood. Removing CO2 from the blood helps increase the pH. Removing HCO3- from the blood helps lower the pH.