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pH 、水温、水质综合指标

pH 、水温、水质综合指标. 时间安排. 预习时，洗净玻璃器皿，将滤膜置入，烘第一遍。 上课前，采集“若谷”学区前的湖水样品，每人装满 1 个矿泉水瓶，上课时带来。 上午上课时，先集中听讲解“称量”，然后分成小组称滤膜，或准备滴定。 集中听讲解 3 个实验。 分头做实验。. 2.2 Determination of pH Value. Purpose:

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pH 、水温、水质综合指标

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  1. pH、水温、水质综合指标

  2. 时间安排 • 预习时，洗净玻璃器皿，将滤膜置入，烘第一遍。 • 上课前，采集“若谷”学区前的湖水样品，每人装满1个矿泉水瓶，上课时带来。 • 上午上课时，先集中听讲解“称量”，然后分成小组称滤膜，或准备滴定。 • 集中听讲解3个实验。 • 分头做实验。

  3. 2.2 Determination of pH Value Purpose: • To understand the principle of pH value measurement, and to master the usage of pH meter and monitoring method.

  4. Questions What is pH? • Definition: pH value is defined as the negative logarithm of hydrogen ion activity in water solution: pH＝－log10aH What is pH range of most natural waters? • The pH value of most natural waters is between 6 and 9.

  5. Method principle • glass electrode: indicating electrode • Ag/AgCl electrode: reference electrode • E = k + 0.0591 lg[H+] = k –0.0591pH where k is the constant • pH = k’- 16.9 E

  6. Apparatus (1) Any types of pH meters or ion activity meters; (2) Glass electrode; (3) Calomel electrode or silver/silver chloride electrode; (4) Magnetic stirring apparatus; (5) Beakers, 50mL, made of polyethylene or polytetrafluoroethylene

  7. Measuring procedure • check pH meter, electrodes and standard solutions • Standardize the meter and electrode with a standard buffer solution • Sample analysis

  8. Key points • Condition the pH electrode • Correct position for the electrode in the solution • rinsetheelectrode

  9. samples • Drinking water • Tap water • Seawater

  10. pH计 pH计属电位法仪器 组成：A、（外）参比电极——甘汞电极； B、玻璃电极 两个参比电极（饱和甘汞电极和玻璃电极的内参比电极）均不受pH影响，受pH影响的是玻璃电极的头。 玻璃电极本身就是一个化学电池。饱和甘汞电极和玻璃电极一起，形成测量回路。 目前pH玻璃电极一般为复合电极，集指示电极和外参比电极于一体，使用方便、牢靠。

  11. pH 测量装置示意图

  12. 离子选择性电极 EISE = E内参＋E膜 = K+0.0591 lg[H+] = k - 0.0591pH pH= (-E+k)/0.0591=k’-16.9E(标准状态)

  13. Ag+AgCl 内部 参比 a内 水化层 干玻璃 水化层 外部 试液 a外 • 玻璃电极 外参比 未知 外水 干玻 内水 内参比 内参比 电极 溶液 合层 璃层 合层 溶液 电极 H+盐桥 H+ 浓度1 浓度2 电位差 玻璃电极 (pH电极)构造： 球状玻璃膜(Na2SiO3 ，厚0.1mm)+ [内参比电极(Ag/AgCl)+缓冲液]

  14. 玻璃膜水化胶层： 干玻璃膜上含Na+。当玻璃膜与纯水或稀酸接触时，由于Si－O与H+的结合力远大于与Na+的，有如下交换反应 ：G-Na+＋ H+   G-H+＋ Na+ • 反应的平衡常数很大，玻璃膜表面形成了水化胶层。 • 玻璃电极的膜电位及电极电位： 形成水化胶层后的电极浸入待测试液，在玻璃膜内外界面与溶液之间均产生界面电位，而在内、外水化胶层中均有扩散电位。膜电位是这四部分电位的总和。

  15. 9 pH pH = k’-16.9E 2个标准溶液， 定位曲线斜率。 实际测量到的， 是∆E= 玻璃电极电位 – 外参比电极电位 7 E

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