过硫酸铵氧化光度法测定微量锰的褪色机理探讨

doi:10.3866/PKU.DXHX202004125

Abstract

Abstract:

The discoloration mechanism of spectrophotometric determination of trace manganese by ammonium persulfate oxidation is discussed in detail through experimental verification. The results show that hydrogen peroxide produced by the thermal decomposition of supersulfate ions leads to the discoloration of permanganate ions, using KIO₄ instead of ammonium persulfate as oxidant to determine trace manganese can not only avoid the fading phenomenon of MnO₄⁻, but also obtain accurate determination results.

Key words: Ammonium persulfate, Trace manganese, Fading mechanism, Potassium periodate

MSC2000:

Enbo Shangguan, Chengke Wu, Jing Li, Suling Feng, Quanmin Li. Study on the Discoloration Mechanism of Spectrophotometric Determination of Trace Manganese by Ammonium Persulfate Oxidation[J].University Chemistry, 2021, 36(4): 2004125.

试验方法及溶液组成	实验操作与现象	结论
I. 总体积40 mL：50 μg?mL^?1 Mn²⁺、1 mol·L^?1 H₂SO和H₃PO₄、2g (NH₄)₂S₂O₈、0.3 mL 0.1 mol·L^?1 AgNO₃	室温下Mn²⁺不能被氧化为MnO₄^?；加入KI-淀粉溶液不变蓝	(NH₄)₂S₂O₈室温下没有氧化性
II. 将I加热煮沸产生紫红色MnO₄^?再继续加热至溶液完全褪至无色，冷却至室温	加入KI-淀粉，溶液变蓝	溶液中有H₂O₂生成，既使MnO₄^?褪色又使淀粉变蓝，见化学反应(2–4)
III. 取2 mL溶液II于10 mL离心管中，加入少许K₂Cr₂O₇，使其溶解，溶液呈浅黄色	在沸水浴加热数分钟，溶液中出现蓝色(CrO₅)后又立即消失	Cr₂O₇^2?被H₂O₂氧化为蓝色CrO₅又快速分解见化学反应(5, 6)
IV. 向溶液II再加入2 g (NH₄)₂S₂O₈	加热至沸数分钟，溶液中不再出现MnO₄^?的紫红色	表明Mn²⁺不能再被氧化，溶液中有H₂O₂生成
V. 室温下总体积40 mL: 50 μg·mL^?1 Mn²⁺ +1 mol·L^?1 H₂SO₄ + 1 mol·L^?1 H₃PO₄ + 1 g KIO₄	加热，Mn²⁺立即被氧化MnO₄^?，继续煮沸30 min，颜色仍不变	在热溶液中MnO₄^?没有被还原Mn²⁺

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Study on the Discoloration Mechanism of Spectrophotometric Determination of Trace Manganese by Ammonium Persulfate Oxidation

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