《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 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 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 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 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. Evaluation only. Created with Aspose.Slides