医用基础化学英文版课件.ppt

4.1.1 The Essential Feature of a Buffer Buffers are mixtures containing a common  ion: either weak acids and their conjugate  bases or weak bases and their conjugate  acid. Two common buffers: ammonium- ammonia, carbonate-bicarbonate NH4+(aq) ? H+(aq) + NH3 (aq) ? CO3-2(aq) + H2O (l) ? H CO3-1 (aq) + OH -1 (aq) A Buffered Solution resists change in its pH when either H+ or  OH? are added. 1.0 L of 0.50 M CH3COOH + 0.50 M CH3COONa pH = 4.74 Adding 0.010 mol solid NaOH raises the  pH of the solution to 4.76, a very minor  change. 4.2 The Henderson-Hasselbalch Equation SOLUTION To prepare the buffer with the volume as more as possible, 2 liter of 0.500mol·L-1 NH3·H2O must be utilized completely, while only a part of the HCl can be used. Let the volume of HCl used be x L, so, the total volume of the buffer prepared is (2.00+x )L. After the neutralization, Preparing a buffer-2 Sample Problem 4- 4 NH3 (aq) + HCl (aq) ? NH4+ (aq) + Cl-(l) Initial(mol) 1.0 0.5V 0 change(mol) -0.5V -0.5V +0.5V Equil-(mol) 1.0- 0.5V 0 0.5V V = 1.3L , so the biggest volume of buffer is 3.3L. Preparing a buffer-2 Sample Problem 4- 4 4.5 Buffering Action in Human Blood The pH of the blood in a healthy individual remains remarkably constant at 7.35 to 7.45. This is because the blood contains a number of buffers that protect against pH change due to the presence of acidic or basic metabolites. From a physiological viewpoint, a change of ±0.3 pH unit is extreme. Acid metabolites are ordinarily produced in greater quantities than basic metabolites, and carbon dioxide is the principal one. The buffer capacity of blood for handling CO2 is estimated to be distributed among various buffer systems as follows: hemoglobin and oxyhemoglobin, 62%; H2PO4-/HPO42-, 22%; plasma protein, 11%; bicarbonate, 5%. Proteins contain carboxylic(羧基) and amino groups, which are weak a