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93 CE Chem 2-21

Can anyone explain to me why the copper wire will have pink colour around it?

I know it's because of the phenolphthalein. But where is the alkali coming from? copper (II) oxide is insoluble in water, Not even iron (III) oxide is soluble in water!

Where does the pink colour come from???


咁d OH- 係邊度黎?

Cu 都唔會 form Cu OH

係 Fe 先會渣嗎!

但係 FeOH 又唔溶水

3 個解答

  • 1 十年前

    Iron is more reactive than copper, and iron prefers to be oxidized to iron(II) ions.

    Fe → Fe2+ + 2e-

    The Fe2+(aq) ions react with the rust indicator to give a deep blue complex.

    Electrons flow from iron to copper. On the surface of copper, oxygen gains electrons to undergo reduction giving hydroxide ions.

    O2 + 2H2O + 4e- → 4OH-

    The presence of OH-(aq) ions make the phenolphthalein turn pink.


  • 匿名
    1 十年前

    Can you give the detail of that question?

    2009-02-07 14:13:55 補充:

    The iron will lossing electrons to form Fe2+ ions. Those electrons will move toward the copper wire as iron is more electropostitve then copper. These electrons is finally donated to oxygen can causes the oxygen reduced to hydroxide ions. So pink colour form around the copper wire.


    Fe ---------->(Fe2+) + 2e-

    O2 + 2H2O + 4e- ---->4OH-

  • 1 十年前

    Fe2+ ion forms blue complex with hexacyanoferrate(iii) while OH- ion around Cu gives pink colour to the phenolphthalein indicator