Using standard reduction potentials, show that one can prepare an ammine complex from CoCl2 and hydrogen peroxide in the presence of ammoinia but not in its absence. (need to write two redux reactions, calculate standard potentials for the reactions, and make conclusions).
I don't know how to set up this problem! Thank you!
To set up this problem, we need to first write the balanced reduction reactions for the species involved. Then, we can calculate the standard reduction potentials for these reactions and draw conclusions based on the obtained values.
Let's start by writing the balanced reduction reactions:
1. CoCl2 + 2e- → Co(s) + 2Cl-
2. H2O2 + 2H+ + 2e- → 2H2O
Now, let's calculate the standard reduction potentials for these reactions. The standard reduction potential, E°, values can be found in a standard reference table or online database.
For reaction 1:
The standard reduction potential for Co2+/Co is +0.28 V.
For reaction 2:
The standard reduction potential for O2/H2O2 is +1.77 V.
Since the reaction occurs in an acidic medium (2H+), we can compare this to the standard reduction potential for O2/H2O, which is +1.23 V.
Now, to make conclusions based on these values:
1. In the presence of ammonia (NH3):
In the presence of ammonia, the CoCl2 will form a coordination complex with ammonia, resulting in the formation of [Co(NH3)6]2+. Since ammonia is not involved in the reduction reactions, we only need to consider the reduction potentials of the other species.
The reduction potential for the formation of [Co(NH3)6]2+ is not relevant to this problem, so we do not need to calculate it. However, since Co has a positive reduction potential (+0.28 V), it is capable of being reduced in the presence of ammonia.
2. In the absence of ammonia:
In the absence of ammonia, the CoCl2 will not form a coordination complex and remain as Co2+. The reduction potential for Co2+ is +0.28 V, indicating that without ammonia, Co2+ cannot be reduced.
Therefore, based on the obtained reduction potentials, we can conclude that the preparation of an ammine complex from CoCl2 and hydrogen peroxide is possible in the presence of ammonia, but not in its absence due to the necessary reduction potential of Co2+.