If pale green FeCl2 solution is left in the open for some time, will some of it gradually oxidise to become brown FeCl3 solution?
Yes, pale green FeCl2 solution can gradually oxidize to become brown FeCl3 solution over time when exposed to the air. This oxidation process occurs because FeCl2, also known as ferrous chloride, is a compound in which iron (Fe) is in the +2 oxidation state, while FeCl3, also known as ferric chloride, is a compound in which iron is in the +3 oxidation state.
The oxidation of FeCl2 to FeCl3 can be explained by the following reaction:
2 FeCl2 + 1/2 O2 + 2 HCl → 2 FeCl3 + H2O
In this reaction, FeCl2 reacts with oxygen (O2) in the presence of hydrochloric acid (HCl) to form FeCl3 and water (H2O).
To confirm whether the pale green FeCl2 solution has indeed oxidized to brown FeCl3 solution, you can perform the following steps:
1. Observe the color change: Over time, if the solution changes from pale green to brown, it indicates oxidation has occurred.
2. Test for the presence of FeCl3: Add a few drops of a reagent such as potassium ferricyanide (K3Fe(CN)6) to a small sample of the solution. If a blue coloration forms, it confirms the presence of FeCl3.
It's important to note that the oxidation process may be slower at lower temperatures and faster at higher temperatures. Additionally, the exposure of FeCl2 solution to moisture, light, and air can also affect the rate of oxidation. To slow down the oxidation process, it is recommended to store FeCl2 solutions in tightly sealed, dark containers to limit exposure to air.