Redox and electrode potentials and transition metals
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Define redox
A reaction in which both reduction and oxidation take place.
Define oxidation
The loss of electrons or an increase in oxidation number.
Define reduction
The gain of electrons or a decrease in oxidation number.
what is an oxidising agent?
The oxidising agent: 1) takes electrons away from the atom that is oxidised 2) contains the atom that is reduced
what is a reducing agent?
a reducing agent: 1) adds electrons to the atom that is reduced 2) is itself oxidised
how can redox reactions be written from oxidation numbers?
increase in oxidation number = decrease in oxidation number for another atom
Why is there no clear colour change at the end point of a Vanadium and Potassium Manganate titration?
KMnO(4) is purple/pink V2+ is violet
What property does the voltmeter have in a cell?
High resistance
Which way does the current flow in the cell?
Negative electrode to the positive electrode
How do the ions flow between cells?
ions flow across the Salt bridge
What is the salt bridge generally made of?
Potassium nitrate (KNO3) Ammonium nitrate (NH4NO3)
What is the electrode made of in a standard hydrogen cell?
Platinum
What is in the half cell of Fe3+ and Fe2+?
Inert Pt electrode and Equimolar Fe2+ and Fe3+ (1 mol dm^-3)
When two half cells are connected, which is oxidised and which is reduced?
More reactive metal is oxidised Less reactive metal is reduced
Define standard electrode potential
The emf of a half cell compared with a standard hydrogen half cell, measured at 298K with solution concentrations of 1 mol/dm^3 and a gas pressure of 100kPa.
What is the electrode potential of a hydrogen half cell?
0.00V
What is the electrode potential of the cell?
Electrode potential of the positive terminal minus the electrode potential of the negative terminal
How do we know if a cell is feasible?
If the electrode potential of the cell is positive, the reaction is feasible.
what’s the Eo of a cell equation?
Eo cell = Eo (positive electrode) - Eo (negative electrode)
what are metal/metal ion half cells?
the half cell is a metal rod dipped in a solution of its metal ion
what is an ion/ion half cell?
An ion/ion half cell is a solution containing ions of the same element in different oxidation states
what is electrode potential?
electrode potential, E, is the tendency for electrons to be gained and for reduction to take place in a half cell
how do you measure a standard electrode potential?
To measure electrode potential, the half cell is connected to a standard hydrogen potential. 1) the electrodes are connected by a wire to allow a controlled flow of electrons through a voltmeter 2) The two solutions are connected by a salt bridge 3) The salt bridge contains ions
what does the more negative the Eo value mean?
The more negative the Eo value 1) it’s more likely to lose electrons and undergo oxidation 2) the less the tendency to gain electrons and undergo reduction