论文总字数：37632字

摘 要

滴定分析法是通过指示剂的颜色变化来确定滴定终点的，指示剂为什么会在滴定过程中发生颜色变化，是值得讨论的问题。在配位滴定中采用金属指示剂，由于金属指示剂同它和金属离子配位后形成的配合物结构不同，所以它们的颜色也不同。

本论文综述了常见的金属指示剂及指示剂变色的敏锐性，并运用EDTA 容量法连续测定钙镁、铁铝混合离子。

连续测定钙镁离子的实验结果如下：

(1)测钙条件为：pH=12~13、K-B指示剂，溶液的颜色由酒红色突变为蓝紫色即为滴定终点；测镁的条件为：pH=10、K-B指示剂，溶液的颜色由蓝紫色突变为亮蓝色即为滴定终点。

(2)分别测定和连续测定均在n_ca² _：n_mg² =3:1时，钙镁离子物质的量测量值与标准加入值之间差值的绝对值最小。分别测定钙镁离子含量时，钙离子差值为3.900×10^-6mol，镁离子差值为7.07×10^-7mol；连续测定钙镁离子含量时，钙离子差值为6.40×10^-7mol，离子差值为5.50×10^-7mol。连续测定的结果优于分别测定。

(3)连续测定时，加入NH₄Cl调节酸度，解决了以往多年来用EDTA连续测定钙镁的系统偏差问题；用HCl调节酸度使系统结果整体偏低。

(4)连续测定时改变指示剂K-B的用量对测定钙和镁的结果几乎没有任何影响。

连续测定铁铝的实验结果如下：

(1)测铁条件为：pH=2、磺基水杨酸指示剂，溶液的颜色由紫红色突变为亮黄色即为滴定终点。测铝条件为：pH=4.3、PAN指示剂、CuSO₄标液，V_EDTA=

10.00~12.50ml，溶液的颜色由亮黄色突变为紫红色即为滴定终点，V_EDTA=17.50~20.00ml，溶液的颜色由亮黄色突变为蓝色即为滴定终点。

(2)连续测定铁含量时，n_Al³ :n_Fe³ ≈0.86:1，Fe³ 物质的量测量值与标准加入值之间的差值的绝对值最小。V_EDTA=10.00~12.50ml，铁离子差值为3.40×10^-8mol；V_EDTA=17.50~20.00 ml, 铁离子的测量值与标准加入值相等。

(3)连续测定铝含量时， pH=4.3、PAN指示剂、CuSO₄标液，n_Al³ :n_Fe³ ≈17:1，Al³ 物质的量测量值与标准加入值之间的差值的绝对值最小。V_EDTA=10.00~

12.50ml，铝离子差值为9.557×10^-7mol；V_EDTA=17.50~20.00ml, 铝离子差值为

2.30×10^-8mol。

关键词 滴定分析法；EDTA容量法 ；钙镁连续测定；铁铝连续测定

ABSTRACT

Titration is used to determine the endpoint by the color change of indicator . The color change of indicator will occur during the titration is worthy of discussion. Metal indicator is used in EDTA titration. Due to the different structure of the metal indicator and metal ion after coordination , their colors are different.

The common metal indicator and the sensitivity of the indicator were described in this paper. EDTA volumetric method was used to measure calcium and magnesium, iron and mixed ions. The corresponding conclusions were got in the experiments.

The continuous determination of calcium and magnesium ions results showed that: (1) measuring calcium conditions: pH = 12~13, K-B indicator, the color of the solution from wine red to blue-violet was the mutated titration end; measuring magnesium conditions: pH = 10, KB indicator, the color of the solution from blue to light blue violet mutation was the titration end point.

(2) Continuous measurement and respective measurement, both in nca² : nmg² = 3:1, the difference of measured value and added value of calcium ion and magnesium ion were the minimum. The respective determination of magnesium and calcium, difference of calcium was 3.900×10^-6mol, difference of magnesium ion was 7.07×10^-7mol; continuous determination of magnesium and calcium, difference of calcium was 6.40×10^-7mol, difference of magnesium ion was 5.50×10^-7mol. And the results are better than respective measurement.

(3)In continuous measurement, NH₄Cl was added to adjust pH, it solved the bias problem of calcium and magnesium in old years. Adjusting the acidity with HCl made the system results low.

(4)In continuous measurement, if the amount of K-B indicator was changed, there’s no effect on the determination of calcium and magnesium.

The continuous determination of iron and aluminum results showed that: (1) measuring iron conditions: pH = 2, sulfosalicylic acid indicator, the color from purple to bright yellow was the endpoint of the titration. Aluminum test conditions: pH = 4.3, PAN indicator, CuSO₄ standard solution, V_EDTA =10.00~12.50ml, the color of the solution from purple to bright yellow was the titration end point, V_EDTA = 17.50~20.00ml, solution color from bright yellow to blue was titration end.

(2) In continuous determination of iron, nAl³ : nFe³ ≈0.86:1, the recoveries of Fe³ substance between the measured value and added value were the best. V_EDTA=10.00~12.50ml, difference of iron ion was 3.40×10^-8mol; V_EDTA = 17.50~20.00ml, iron ion difference was the same.

(3) Continuous determination of aluminum, pH = 4.3, PAN indicator, CuSO₄ standard solution, the measured value and the Standard addition value of aluminum ion was the minimum, the recovery was the best. V_EDTA = 10.00 ~12.50ml, difference of aluminum ion was 9.557×10^-7mol; V_EDTA =17.50~20.00ml, difference of aluminum ion was 2.30×10^-8mol.

Keywords Titration analysis methods; EDTA volumetric methods; Continuous measurement of calcium and magnesium; Continuous measurement of iron and aluminum.

目录

摘 要 I

ABSTRACT III

目录 V

第一章 文献综述 1

1.1 EDTA络合滴定简介 1

1.2 混合金属离子连续测定的研究进展 1

1.3常用的金属指示剂 4

1.3.1 K-B指示剂（酸性铬蓝K-萘酚绿B） 4

1.3.2 钙黄绿素-百里酚酞指示剂 4

1.3.3 磺基水杨酸指示剂 4

1.3.4 PAN指示剂 5

1.3.5铬黑T指示剂 5

1.3.6二甲酚橙指示剂 5

1.4 研究目的和意义 5

第二章 实验部分 7

2.1 实验仪器与试剂 7

2.1.1 实验仪器 7

2.1.2 实验试剂 7

2.2 实验方法 8

2.2.1 Ca² 标准溶液标定EDTA溶液 8

2.2.2 水的硬度测定 9

2.2.3连续测定钙和镁 10

2.3.4分别测定钙和镁 10

2.2.5 Zn² 标准溶液标定EDTA溶液 10

2.2.6 Fe³ 、Al³ 、Cu² 标准溶液的配制及其浓度的测定 11

2.2.7 EDTA容量法连续测定铁和铝的实验方法 12

第三章 实验结果与讨论 14

3.1 EDTA容量法连续测定钙镁的实验 14

3.1.1 Ca² 标定EDTA溶液 14

3.1.2 Mg² 浓度标定 14

3.1.3水的硬度测定 15

3.1.4分别测定与连续测定钙和镁的结果与讨论 16

3.2 EDTA容量法连续测定铁铝的实验 22

3.2.1 Zn² 标准溶液标定EDTA溶液 22

3.2.2Fe³ 、Al³ 、Cu² 溶液浓度的标定 22

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