基础化学-梁逸增-第四章课件.ppt

; 本章教学内容;内容提要:;重点:;— solutions that resist change in hydronium  ion, H+, and the hydroxide ion,OH-,  concentration (and consequently pH) upon  addition of small amounts of acid or base,  or upon dilution. ; 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) ? CO32- (aq) + H2O (l) H CO3-(aq) + OH- (aq) ;共轭酸;Buffer system;Tris: Tris(Hydroxymethy)methanamin;? 下列情况均需pH一定的缓冲溶液： ? 大多数为酶所控制的生化反应 ? 微生物的培养 ? 组织切片 ? 细胞染色 ? 药物调剂、研制等;Buffer with equal concentrations of conjugate base and acid;HAc + H2O ;The amounts of weak acid and weak base in the buffer must be significantly larger than the amounts of H3O+ or OH- that will be added, otherwise the pH cannot remain approximately constant. Thus addition of limited amounts of a strong acid or base is counteracted by the species present in the buffer solution, and the pH changes very little. No solution can keep the pH approximately constant if you add larger amounts of either acid or base that are present in the original buffer. ;For a HB-NaB buffer system,;pH = pKa + lg ;pH = pKa + lg;如果用活度代替浓度，;Calculating the pH of a Buffer Solution-1;SOLUTION;After the addition of 0.005mol of NaOH(s) to 500 mL of the buffer solution;例4-2： 将0.10 mol·L-1 的 H3PO4溶液20 mL与 0.10 mol·L-1 的 NaOH溶液30 mL混合，混合溶液是缓冲溶液吗? 求混合溶液的pH。已知：pKa1=2.16, pKa2=7.21, pKa3=12.32。;4.3.1 The Concepts of Buffer Capacity;where β is the buffer capacity and has units of moles per liter per pH (mol·L-1·pH-1); dna (or b) stands for moles of strong acid or strong base which are added to a buffer solution to cause the change in pH, dpH.;The following can be derived from above one：;4.3.2 Factors Affecting Buffer Capacity;When Ctotal if fixed：;因为， ? = 2.303?[HB][B–] / c总;When the buffer ratio, c(B-)/c(HB), is fixed, the more