Ferroxyl indicator is a solution containing potassium hexacyanoferrate(III) and phenolphthalein. It turns blue in the presence of Fe2+ ions, and pink in the presence of hydroxide ions. It can be used to detect metal oxidation, and is often used to detect rusting in various situations.
![](http://upload.wikimedia.org/wikipedia/commons/thumb/9/9d/Corros%C3%A3o_de_ferro_por_sacrif%C3%ADcio_em_contacto_com_cobre.jpg/220px-Corros%C3%A3o_de_ferro_por_sacrif%C3%ADcio_em_contacto_com_cobre.jpg)
It can be prepared by dissolving 10g sodium chloride and 1g potassium hexacyanoferrate(III) in distilled water, adding 10 cm3 phenolphthalein indicator, then making up to 500 cm3 with distilled water.[1]
References
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