Buffer Solution HAc H 2 O Na Ac

第四章 缓 冲 溶 液 (Buffer Solution)

一、缓冲机制 HAc + H 2 O Na. Ac HAc + H 2 O 大量 H 3 O+ + Ac→ Na+ + Ac. H 3 O+ + Ac- 同 离 子 效 应 大量 共轭碱(conjugate base) 抗酸成分 (anti -acid component)

HAc + H 2 O 大量 共轭酸 （conjugate acid） 抗碱成分 (antibase component) H 3 O+ + Ac大量

常用缓冲系 HB + H 2 O （conjugate acid ） NH 4 Cl H 3 PO 4 Na. H 2 PO 4 Na 2 HPO 4 H 2 CO 3 Na. HCO 3 H 3 BO 3 HAc B - + H 3 O + (conjugate base) —— —— NH 3 Na. H 2 PO 4 Na 2 HPO 4 Na 3 PO 4 Na. HCO 3 Na 2 CO 3 Na. H 2 BO 3 Na. Ac

CO 2(溶解) + H 2 O H 2 CO 3 H+ + HCO 3 - 大量 大量 conjugate acid conjugate base anti-acid component anti-base component

（1）HCl （2）0. 1 mol·L-1 HAc+Na. OH （3）0. 2 mol·L-1 HAc+Na. OH（4）0. 05 mol·L-1 KH 2 PO 4+Na. OH （5）0. 05 mol·L-1 H 2 BO 3+Na. OH（6）Na. OH

四、标准缓冲溶液 溶液 KHC 4 H 4 O 6 KHC 8 H 4 O 4 KH 2 PO 4 -Na 2 HPO 4 p. H(25 o. C) 温度系数 (△p. H/ o. C) 饱和, 25 o. C 3. 557 -0. 001 0. 05 4. 008 +0. 001 0. 025, 0. 025 6. 865 -0. 003 浓度/ mol·L-1 0. 008695 , 0. 03043 0. 01 （Na 2 B 4 O 7· 10 H 2 O） 7. 413 -0. 003 9. 180 -0. 008

Summary A solution that could withstand the effect of a few additional strong acid or strong base and keep its p. H changeless is called buffer solution. Ⅰ The composition of a buffer Usually a buffer consists of large numbers of two components of a conjugate acid-base pair.

conjugate acid → anti-base component conjugate base → anti-acid component When small amounts of strong acid are added ，the conjugate base can withstand the additional strong acid without changing its p. H ; When small amounts of strong base are added ，the conjugate acid can withstand the additional strong base without changing its p. H.

Ⅱ How to calculate the p. H of a buffer Henderson-Hasselbalch equation: p. Ka——the p. Ka of the conjugate acid buffer component ratio

Ⅲ Buffer capacity Definition: The buffer capacity depends on the concentration of the components and buffer component ratio. The more concentration the components of the buffer, the greater the buffer capacity.

A buffer has the highest capacity when its components are present in equal concentration , that is, when [B-]/[HB]=1. Buffer effective range is from p. Ka-1 to p. Ka+1, that is, p. H=p. Ka-1 ~ p. Ka+1

Ⅳ How to prepare a Buffer 1) Choose the reasonable conjugate acidbase pair 2) Calculate the ratio of buffer component 3) Determine the buffer concentration 4) Adjust the final buffer to the desired p. H