top of page

Redox II

Quick Points:

  • -  Make sure to always to 2 d.p.

  • -  Remember finer details like washing the burette with acid etc.

  • -  They may add acid to a standard solution which can just be to catalyse it make sure not

    to get thrown off

  • -  To make sure that all is transferred make sure to rinse

  • -  Note than multiplying by moles in a half equation is not going to increase the Eo or need

    multiplication

    Weaknesses:

  • -  Standard Electrode Potential: the emf of that half-cell relative to a standard hydrogen

    electrode under standard conditions. (may be called standard redox potentials)

  • -  Standard Conditions: 298K, 100kPa, 1 mol dm-3 concentration (of ions)

  • -  Standard Hydrogen Electrode: a half-cell is a cell in which a 1 mol dm-3 solution of

    hydrogen ions is in equilibrium with hydrogen gas under standard conditions

    • -  It will be the left electrode in an electrochemical cell

    • -  It is presented such that there will be a Hydrogen gas inlet at the top of a test

      tube or cover inverted over a platinum electrode in a beaker with a solution of acid solution to provide the H+ ions and the glass cover and inlet providing the Hydrogen gas will provide the hydrogen to react with this and form equilibrium

    • -  NOTE: platinum electrode is required as the reactant is gas

  • -  Hydrogen is a reference electrode but as it is difficult to maintain often a silver/silver

    chloride electrode or a calomel electrode may be used. A reference electrode is required to enable comparison between different electrodes and to enable controlled regulation over working electrode potential. Furthermore there is no way of measuring the emf in a single cell and this is required to harness emf and use it (in batteries etc.) As a result the standard hydrogen electrode was given the arbitrary emf value of 0.00 V

  • -  Standard writing of an electrochemical cell is ROOR with a | as a state change/phase boundary and || as a salt bridge

  • -  More negative goes on the left and the more positive goes on the right

  • -  Ecell(emfofagivencell)=Eright-Eleft

  • -  A more positive the standard electrode potential of a given half-reaction the more likely it

    is that this reaction will occur

  • -  Halogen molecules and halide molecules are always positive F is the most positive as it

    is the most reactive and then it decreases in positivity

  • -  Trend appears as a result of them undergoing displacement reactions

  • -  Note that for predicting direction: the more positive half equation will tend to go from left

    to right and gain electrons and the more negative will go from right to left

    Storage Cells:

- Lead Acid Cells:

  • -  Used to give power to motor battery operated vehicles such as electric scooters etc.

  • -  Negative terminal is lead with an electrolyte of sulfuric acid (semi-conc), The lead is oxidised forms a lead (II) sulphate precipitate

  • -  The positive terminal is lead oxide that reacts with the H+ ions to and lead (II) sulphate precipitate is again formed

  • -  Voltage of 2

  • -  Issue is that as the lead (II) sulphate is formed if left unused much of the lead (II)

    sulphate formed will solidify and prevent the equilibrium fro, restarting

- Disadvantage: the emf drops over time as the PbSO4 build over time on

the electrodes.

- Lithium Cells:

  • -  Modern mobile phones and laptop computers use lithium batteries

  • -  Quite light as lithium has a low density

  • -  Difficulty is readily combines with air forming an oxide which is non-conducting

  • -  Also combines with water

  • -  So instead is placed in a crystal lattice and other lattices and the electrolyte is a

    polymeric material as opposed to an aqueous solution

  • -  Material is polymeric material as opposed to an aqueous solution

- Disadvantage: the emf drops over time

- Fuel

  • -  Reaction between a fuel and oxygen

  • -  Have a continuous stream of reactant

  • -  Hydrogen-oxygen fuel cell is one of the most commonly used ones

  • -  E.g.

- In acidic conditions hydrogen will be pumped in and oxidised to H+ and this will pass through the electrolyte and react with oxygen which is reduced to ions to form water

  • -  Advantage: considerable lighter so more efficient as easier to carry and thus more mileage (often assessed)

  • -  Emf is constant as the reactants are regenerated continually

- Disproportionation: single species both oxidised and reduced. The half equation for the species that would be oxidised and reduced is reversed and added to the second half equation to get an E cell value for disproportionation. A positive value is feasible

bottom of page