Electrode potentials Flashcards
What is an electrochemical cell?
- a cell which converts chemical energy into electrical energy
- this requires a redox reaction as the electrical energy comes from the movement of electrons
What is a half cell?
- a half cell contains the chemical species present in a redox half equation
- An electrochemical cell can be made by connecting two different half cells which allows electrons to flow
What is a metal/ion half cell?
- consists of a metal rod dipped into a solution of aqueous metal ions
How do you draw a phase boundary?
- A vertical line is used to show the phase boundary between the metal and aqueous solution
- for example Zn2+(aq) [ Zn (s)
- aqueous ions are on the left
- at the phase boundary, the metal is contact with its ions and therefore an equilibrium is set up
What is the flow of electrons?
- depends on the tendency of which electrode loses or gains electrons
- it flows from oxidation to reduction
What are the rules of drawing an electrochemical cell?
- the more reactive element that is oxidised is on the left, more negative
- the more positive element is on the right
- ensure there is a salt bridge dipped into the aqueous solutions (AgNO3)
- the salt bridge does not interfere with the reaction and allows the ions to flow
- ensure the electrodes are dipped in the aqueous solution
What is the format of oxidation half equations? (with zinc)
Zn (s) = Zn2+ (aq) + 2e-
What is the format of reduction half equation? (with copper)
Cu2+(aq) + 2e- = Cu(s)
How do you draw an ion/ion half cell?
- an ion/ion half cell contains ions of the same element in different oxidation states
- for example: Fe3+ (aq) + e- = Fe2+ (aq)
- use pt electrode dipped into the aqueous solution
- platinum is used as it is inert metal electrodes
What are the different electrodes?
- The electrode that is more reactive loses electrons and is oxidised, this is the negative electrode
- The electrode that is less reactive and is reduced, this is the positive electrode
How do you calculate standard electrode potentials?
standard electrode potential = the tendency to gain electrons and to be reduced
- This can be calculated by connecting the half cell to a standard hydrogen half cell under standard conditions (298K, 1 mol dm-3, 100KPA)
- The standard half cells contains hydrogen gas (H2) and is in a solution of H+ (aq). An inert plantinum electrode is required to allow electrons into and out of half cells
- The standard electrode potential of a standard hydrogen electrode is 0v
- When connected to a standard hydrogen electrode, you can determine the relative tendency to gain or lose electrons
Draw a standard hydrogen electrode.
The more negative the electrode..?
- the greater the tendency to lose electrons and undergo oxidation
- the less the tendency to gain electrons and undergo reduction
The more positive the electrode..?
- the greater the tendency to gain electrons and undergo reduction
- the less the tendency to lose electrons and undergo oxidation
The more negative the E value the..?
the greater the reactivity the reactivity of a metal in losing electrons
How do you calculate the standard cell potential from standard electrode potentials?
E cell = E(positive electrode) - E(negative electrode)
