What Happens
* Initial Reaction: The initial reaction leads to the formation of iron(III) thiosulfate (Fe₂(S₂O₃)₃). This is a double displacement reaction:
3 Na₂S₂O₃(aq) + 2 Fe(NO₃)₃(aq) → Fe₂(S₂O₃)₃(s) + 6 NaNO₃(aq)
* Decomposition: Iron(III) thiosulfate is unstable and quickly decomposes in aqueous solution. This decomposition leads to the formation of sulfur, sulfur dioxide, and iron(II) ions (Fe²⁺).
Fe₂(S₂O₃)₃(s) + 6 H₂O(l) → 2 Fe²⁺(aq) + 3 S(s) + 3 SO₂(g) + 6 OH⁻(aq)
Overall Equation:
Combining the initial reaction and decomposition, the overall reaction is:
3 Na₂S₂O₃(aq) + 2 Fe(NO₃)₃(aq) + 6 H₂O(l) → 2 Fe²⁺(aq) + 3 S(s) + 3 SO₂(g) + 6 NaNO₃(aq) + 6 OH⁻(aq)
Key Points:
* Sulfur Precipitate: You will observe a yellow precipitate of sulfur (S) forming in the solution.
* Sulfur Dioxide Gas: Sulfur dioxide (SO₂) is a colorless gas with a pungent odor, and it will be released into the air.
* pH Change: The solution will become more basic (higher pH) due to the formation of hydroxide ions (OH⁻).
Important Note: This reaction is not a simple double displacement, and the products are not just iron(III) thiosulfate and sodium nitrate. The instability of iron(III) thiosulfate leads to a complex decomposition that results in sulfur, sulfur dioxide, and iron(II) ions.
