Test: Test of Fe2+ and Fe3+ - JAMB MCQ

Ammonium hydroxide is commonly used to test for the presence of Fe²⁺ ions. When ammonium hydroxide is added to a solution containing Fe²⁺ ions, a light green precipitate of iron(II) hydroxide [Fe(OH)₂] is formed. This precipitation reaction is a characteristic test for Fe²⁺ ions.

Fe3⁺ ions can be reduced to Fe²⁺ ions by adding a reducing agent. Zinc (Zn) is commonly used as a reducing agent in this context. When zinc is added to a solution containing Fe³⁺ ions, the zinc reacts with Fe³⁺ ions, transferring electrons and reducing Fe³⁺ to Fe²⁺.

When Fe²⁺ ions are oxidized to Fe³⁺ ions, the color of the solution changes from pale green to orange-brown. This color change is due to the formation of the Fe³⁺ ion, which has an orange-brown color in solution.

Redox titration can be used to distinguish between Fe²⁺ and Fe³⁺ ions. In a redox titration, a reducing agent is used to reduce Fe³⁺ to Fe²⁺ or an oxidizing agent is used to oxidize Fe²⁺ to Fe³⁺. By measuring the amount of reducing or oxidizing agent required to reach an equivalence point, the oxidation state of iron can be determined.

When Fe²⁺ ions react with potassium manganate(VII) (KMnO₄) in an acidic medium, Fe²⁺ ions are oxidized to Fe³⁺ ions, and the MnO₄^- ions are reduced to brown manganese dioxide (MnO₂). This reaction is commonly known as the "iodometric titration."

When potassium thiocyanate (KSCN) is added to a solution containing Fe³⁺ ions, a deep red color is observed. This color change occurs due to the formation of a complex ion called iron(III) thiocyanate (Fe(SCN)₃), which has a reddish-brown color.

Fe³⁺ ions do not exhibit a blue color in solution. They are typically pale yellow or orange-brown in color. Blue color in solution is associated with certain other transition metal ions like Cu²⁺.

The potassium ferrocyanide test is a confirmatory test for the presence of Fe³⁺ ions. When potassium ferrocyanide is added to a solution containing Fe³⁺ ions, a deep blue precipitate of iron(III) ferrocyanide (Prussian blue) is formed.

When Fe2⁺ ions react with potassium thiocyanate (KSCN), the complex ion formed is iron(II) thiocyanate, which is represented as Fe(SCN)²⁺. The Fe²⁺ ion combines with the SCN^- ion to form this complex.

In the oxidation of Fe²⁺ ions to Fe³⁺ ions, each Fe³⁺ ion gains 2 electrons. This process involves the transfer of electrons from Fe²⁺ to an oxidizing agent, resulting in the formation of Fe³⁺ ions.