Transition Metala - redox potential and vanadium chemistry Flashcards
what happens when TMs change oxidation state
A REDOX reaction occur and the colour changes.
why do TMs have variable oxidation states. and what does it result in
TMs have their electrons sitting in 4s and 3d eneergy levels, these two very close to each othe.
- as a result electrons are gained and lost using a similar amount of energy when they form ions.
- so they have variable OS.
what ions can vanadium form, and what is the OS of V in each one and what colour solution does each one form when dissolved in water ?
VO2^+ Oxidation state +5 - yellow solution
VO^2+ Oxidation state + 4 - blue solution
V^3+ Oxidation state + 3 - green solution
V^2+ Oxidation state + 2 - violet solution
what is used to reduce vanadium (V) ions (VO2^+) all the way to Vanadium (ii) ions (V^2+)
using Zinc (=strong reducing agent) in an acidic solution.
give the equation of the reaction when VO2^+ gets reduced to VO^2+
- this same equation will apply to the other reductions, just with the starting ion and final product being different.
VO2^+(aq) + Zn(s) + 4H^+(aq) -> VO^2+(aq) +Zn^2(aq)+ + 2H2O(l)
recap - what are redox potentials
tells us how easily an ion is reduced = the same as the ectrode potnetial
comment on the redox potnetial of the least stable ions
the leasst stable ions have the largest redox potential and so are more likely to be reduced.
what are the standard conditions for when electrode potnetials values are calculated
- temperature = 298K
- pressure at 100KPa
- concentrations of ions as 1 moldm-3
why might there be a differecne in redox potnetialas when compared to the standard values seen in a data book
cos it depends on the environment the ions are in.
what 2 factors affect redox potentials
the ligand and the pH
what solutions (and lignads are presnet) used when standard electrode potentials are mesuared.
Aqueous solutions = the metal ion is surrounded by water molecules.
how can ligands other the water have an effect on the theoretical electrode potnetial value
ligands other than water can form stronger bonds (like CN or CO) with the metal ion with particular oxidation states, this means the redpx potnetial can be higher or lower then the standard value.
How can pH affect the redox potentials of some reactions.
the more acidic the solutions, the larger the electrode potential = the ion is more easily reduced.
Here the H+ ions are required for the reduction of MnO2 to Mn^2+
here the OH- ions are produced into solution when reduced =
PbO2(aq) + H2O(l) + 2e- <-> PbO(aq) + 2OH-(aq)
what Does Ag+ having a large electrode potnetial value mean
it means the Ag+ can be reduced to Ag = silver metal easily.
what is tollen’s made by ?
Tollens is made by reacting enough aquous ammonia to aquous silver nitrate. colourless [Ag(NH3)2] is produced.
