6. variable oxidation state

transition metals exist in variable oxidation states

switching between oxidation states is a redox reaction where the metal ions are either oxidised or reduced

vanadium oxidation states

+2 +3 +4 +5

vanadium V can be reduced by adding it to zinc metal in an acidic solution

redox potential

how easily an ion or atom is reduced to a lower oxidation state

redox potential is the same as

electrode potentials

the more positive the redox potential

the less stable the ion will be and so the more likely it is to be reduced

Copper II has a redox potential of +0.15V, so its less stable than Chromium and more likely to be reduced than chromium

redox potentials in a table

are standard electrode potentials measured with reactants at concentration of 1 mol^-3 against SHE under standard conditions

redox potential of an ion wont always be the same as its standard electrode potential

it can vary depending on the environment of the ion

standard electrode potentials are measured in aqueous solutions

so any ions will be surrounded by water ligands

different ligands may make the redox potential larger or smaller

depending on how many will bind to the metal ion in a particular oxidation state

some ions need H⁺ ions present in order to be reduced

other ions release OH^- ions into solution when they’re reduced

silver is a transition metal commonly found in +1 oxidation state Ag⁺

it is easily reduced to silver metal

tollens reagent preparation:

adding just enough ammonia solution to silver nitrate to form a colourless solution containing [Ag(NH₃)₂]⁺

when tollens is added to aldehydes

it reacts to give a silver mirror inside the test tube

the aldehyde is oxidised to a carboxylate anion

Ag⁺ ions are reduced to silver metal

RCHO + [Ag(NH₃)₂]⁺ + 3OH^- →

RCOO^- +2Ag +4NH₃ + 2H₂O

tollens reagent cant oxidise ketones

so it will not react to form a silver mirror