Photochemical reaction with ferrioxalate lab ferrioxalate solution is in all 6 o
ID: 894818 • Letter: P
Question
Photochemical reaction with ferrioxalate lab
ferrioxalate solution is in all 6 of the test tubes, 6 drops ofpotassium ferricyanide was added and mixed
During the trials involving the test tubes and flood lights, one test tube was not irradiated, some were irradiated with white light, and one was irradiated only with red light. I need help explaining these results in terms of absorption measurements.
Results:
test tube 1: not irradiated - very faint green was observed
2: exposure to white light for 5 sec- turned darker than test tube 1
3: exposure to white light for 10 sec- turned darker than test tube 2
4: exposure to white light for 20 sec- turned darker than test tube 3
5. exposure to red light for 10 sec- very faint green like test tube 1
6: test tube blaced in boiling water - very dark green colour
Please help with reason why this happens?
Explanation / Answer
The chemical reaction here occuring is, the ferrioxalate complex in solution absorbs light at the blue end (in white light) of the visible light spectrum resulting in an internal electron transfer reaction in which Fe3+ is reduced to Fe2+. Potassium ferricyanide, K3[Fe(CN)6], then reacts with the Fe2+ ions to produce a component with a deep blue/green colour. This allows us to detect if the ferrioxalate complex has undergone photochemical reduction and also gives the blue colour in the blueprint.
Now with this background let us answer the following,
test tube 1. : not irradiated - very faint green was observed : when no light is absorbed (not irradiated) the solution shows almost no reduction reaction and thus very faint coloration to the solution seen.
test tube 2. exposure to white light for 5 sec : part of ferrioxalate absorbs light, reduces Fe3+ to Fe2+ which then reacts with the added ferricyanide to give darker coloration to the solution.
test tube 3. : exposure to white light for 10 sec : more of ferrioxalate here absorbs light and leads to greater reduction of Fe3+ to Fe2+. As the amount of Fe2+ formed here is larger than test tube 1., we see more dark the solution is when reacted with potassium ferricyanide.
test tube 4. : exposure to white light for 20 sec : the solution gives even more reduction of Fe3+ to Fe2+. More Fe2+ means more reaction with added potassium ferrricyanide to give stronger coloration to the solution.
test tube 5. : exposure to red light for 10 sec : as has been discussed above, an absorption near the blue end of the visible light yields Fe2+ from Fe3+ in the reaction. Red light will not be absorbed and hence almost no reaction was seen here.
test tube 6. : test tube placed in boiling water : the reduction of Fe3+ to Fe2+ needs energy, which is supplied in terms of the light. An alternate option is to supply this energy in the form of heat. Both the reactions would proceed in a similar fashion. Thus when heated we get reduction of Fe3+ to Fe2+ which then reacts with potassium ferricyanide to give green coloration to the solution.