第三章滴定概论解析

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Grade Chinese English Label Use
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I 优级纯 GR green H. Anal. exp
II 分析纯 AR red Anal. Exp.
III 化学纯 CP blue Chem. exp.
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3C Titrition curves

A graph showing the progress of a titration as a function of the volume of titrant added.
Acid–base titration curve for 25.0 mL of 0.100 M HCl with 0.100 M NaOH
滴定分析法对化学反应的要求

Three conditions need to be met:

All reactions involving the titrant and analyte must be
of known stoichiometry. 有确定的化学计量关系，反应按一定的反应方程式进行
Example 2

称取铁矿石试样 0.5000g ，将其溶解，使全部铁还原
为 Fe2+ ，用 0.01500mol· L-1 K2Cr2O7 标准溶液滴定至
化学计量点时，用去 K2Cr2O7 标准溶液 23.45mL ，求 试样中Fe和Fe2O3的质量分数分别为多少？
解 6Fe2+ +Cr2O72- +14H+ = 6Fe3+ +2Cr3+ +7H2O

The titration reaction must occur rapidly. 反应速度较快

A suitable indicator must be available for determining the end pof accuracy.
Zn2+
Zn—EDTA
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Example 1

称 取 含 铝 试 样 0.2000g ， 溶 解 后 加 入 0.05082mol· L-1 EDTA标准溶液20.00mL，控制条件使Al3+与EDTA络 合完全，然后用 0.05012mol· L-1Zn2+ 标准溶液返滴定， 消耗 Zn2+ 溶液 11.36mL ，计算试样中 Al2O3 的质量分 数？

Consumed volume should not be too small. Experiment should be repeated at least 3 times.
Relative error should be within 0.2%.
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nNa S O 6nK Cr O
2 2 3 2 2
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Example of indirect titration:
如Ca2+沉淀为CaC2O4，再用硫酸溶解，用KMnO4滴
定C2O42-,间接测定Ca2+
第三章
滴定分析概论
Titrimetric methods of analysis
滴定分析法：又称容量分析法。 标准溶液
化学计量关系 指示剂
标准溶液
被测物质 酸碱滴定法、 络合滴定法 氧化还原滴定法、沉淀滴定法
待测溶液
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nFe2 6nCr O 2 2nFe2O3
2 7
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wFe
nFe2 M Fe ms

6nK 2Cr2O7 M Fe ms

6cK 2Cr2O7 VK 2Cr2O7 M Fe ms
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Example of displacement titration:
Na2S2O3 can be oxidized or reduced. Too much side reaction.
解
nAl3 nEDTA 2nAl2O3
wAl2O3
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nZn 2 nEDTA
1 (0.05082 20.00 0.0501211.36) 103 102.0 2 0.1140 0.2000
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Secondary standard：

a compound whose purity has been established by chemical analysis and serves as the reference material for a titrimetric method of analysis.
containing the analyte, and the excess reagent remaining after
its reaction with the analyte is determined by a titration

置 换 滴 定 法 Displacement titration: In which, the analyte displaces a species, usually from a complex, and the amount of the displaced species is determined by a titration.络合滴定多 用 间接滴定法 Indirect titration: no available direct titration reaction.
6 0.01500 23.45103 55.85 0.2357 0.5000 1 1 nFe2O3 M Fe2O3 2 nFe2 M Fe2O3 2 6nK 2Cr2O7 M Fe2O3 wFe2O3 ms ms ms 3 0.01500 23.45103 159.7 0.3370 0.5000
容易确定滴定终点
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滴定方式 Titration strategies

直接滴定法 Direct titration: meet above three conditions. 返滴定法 Back titration: slow reaction, solid sample, or no available indicator. In which a reagent is added to a solution
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Example of a redox titration curve
Example of a thermometric titration curve
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3B Standard solutions 标准溶液 标准溶液: 已知准确浓度的试剂溶液。 配制方法有直接配制和标定两种。

3B-1 Desirable properties of standard solution
2 2Cr2 O 7 S2 O 3 No stoichiometrical
6I 3 ( I2

reaction
22 2S2 O3 2I S4 O 6 )
nCr O2 1 nI- 1 2nI2 1 1 nS O2 1 nS O2 2 7 6 6 3 2 2 3 6 2 3
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3A-2 基准物质 Primary standard: purchased
基准物质: 能用于直接配制和标定标准溶液的物质。 要求：试剂与化学组成一致；纯度高；稳定；摩尔质量大； 滴定反应时无副反应。 Biochem. Reagent BR coffee Biochem. & Medchem. exp
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Example of back titration:
如测定CaCO3，加入过量盐酸，多余盐酸用标准氢氧化钠 溶液返滴
Measurement of solid sample CaCO3.
S
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