RUSTING PROBLEM CHEM!!!

[匿名]

2011-04-28 12:33 am

Rusting 本身果條formula係：
４Fe+3O2+2xH20----->2Fe2O3.xH20

想問點解rust indicator里面的K3Fe(CN)6 test 的野係Fe2+?

同埋rust indicator 仲有phenolphthalein , 佢test 的野係OH-

本身條formula都無fe2+ 同OH- form 點解rust indicator 可以sense到rust?

仲有點解rusting 過程會form 到Fe2+ 同OH-?

更新1:

thx 唔該大家

回答 (1)

己式庚辛

2011-04-28 8:29 am

✔ 最佳答案

because that's only the overall formula of rusting.
in fact, rusting is a multi-step reaction, involving formation of Fe(II) and OH(-) as intermediates.

2Fe + O2 + 2H2O ----> 4OH(-) + 2Fe(2+) ------> 2Fe(OH)2
4Fe(OH)2 + O2 + 2H2O ------> 4Fe(OH)3

in these intermediate reactions, Fe(II) and hydroxide are formed; while trace of these species can be detected by rust indicator (kind of pale yellow) and phenolphthalein.
2[Fe(CN)6](3-) + 3Fe(2+) ------> Fe3[Fe(CN)6]2 (blue solid in gel)

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