When the iron(II) ammonium sulfate was mixed with the ferrocyanide ion, the precipitate was initially white but turned blue upon exposure to air. What happened to iron(III) ion when the precipitate turned blue?
Iron(II) is oxidized by air to iron(III).
When iron ii turned blue it indicates that there was mixture with oxygen which increased the number to iron iii
When the iron(II) ammonium sulfate was mixed with the ferrocyanide ion, a reaction occurred that led to the formation of a precipitate. Initially, the precipitate was white indicating the presence of iron(II) ion.
However, upon exposure to air, the precipitate turned blue. This color change suggests that the iron(II) ion present in the precipitate was oxidized to form iron(III) ion.
The reaction can be summarized as follows:
2 Fe^2+ + 3 [Fe(CN)6]^4- + 4 H2O → 2 Fe3 [Fe(CN)6]2 + 12 H+
In this reaction, the ferrocyanide ion ([Fe(CN)6]^4-) oxidizes the iron(II) ion (Fe^2+) to iron(III) ion (Fe^3+). The resulting compound, iron(III) hexacyanoferrate(II), is a blue-colored complex.
Therefore, the observation of a blue precipitate upon exposure to air indicates the presence of iron(III) ion in the solution.
The change in color of the precipitate from white to blue upon exposure to air indicates the formation of Prussian blue, a deep blue pigment. It is formed when the iron(II) ions in the iron(II) ammonium sulfate react with the ferrocyanide ions (Fe²⁺ + 4[Fe(CN)₆]⁴⁻) present in solution.
To better understand this reaction, let's go step by step:
1. Iron(II) ammonium sulfate, also known as Mohr's salt, is a compound that contains iron(II) ions (Fe²⁺) and ammonium sulfate ions ([NH₄]₂SO₄). It is typically white in color.
2. When this compound is mixed with a solution containing ferrocyanide ions ([Fe(CN)₆]⁴⁻), a double displacement reaction occurs. The iron(II) ions react with the ferrocyanide ions, resulting in the formation of a precipitate.
3. Initially, the precipitate is white. This is because the reaction product at this stage is iron(II) hexacyanoferrate(II), also known as white precipitate or Turnbull's blue. It has the chemical formula Fe[Fe(CN)₆].
4. However, when this white precipitate is exposed to air, a redox reaction takes place. The iron(II) ions in the precipitate are oxidized by atmospheric oxygen, forming iron(III) ions (Fe³⁺).
5. The presence of iron(III) ions leads to the formation of Prussian blue, a highly colored complex compound. It traps the iron(III) ions within its structure and imparts a blue color to the precipitate.
In summary, when the white precipitate (iron(II) hexacyanoferrate(II)) formed from the reaction of iron(II) ammonium sulfate and ferrocyanide ions is exposed to air, it undergoes oxidation, resulting in the formation of iron(III) ions. The presence of iron(III) ions then leads to the formation of Prussian blue, which gives the precipitate a blue color.