University Chemistry ›› 2021, Vol. 36 ›› Issue (4): 2004125.doi: 10.3866/PKU.DXHX202004125
• Chemistry Laboratory • Previous Articles Next Articles
Enbo Shangguan1,2, Chengke Wu2,*(), Jing Li2, Suling Feng2, Quanmin Li2
Received:
2020-04-30
Accepted:
2020-06-28
Published:
2020-07-21
Contact:
Chengke Wu
E-mail:ckwu0304@163.com
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.
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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 | Cr2O72?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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