OCR Transition Elements

What does a half-cell contain?

Either…

An element electrode in contact with its aqueous ions

Or…

Two different aqueous ions of the same element in different oxidation states using platimum as the electrode.

Define the standard electrode potential of a half-cell (Eθ).

The standard electrode potential of a half-cell is the voltage of a half-cell compared with a standard hydrogen electrode.
What is the standard electrode potential of a half-cell a measure of? What are it units?
The standard electrode potential of a half-cell is a measure of the ease with which one oxidation state in a half-cell can be converted into another oxidation state. Standard electrode potential is measured in volts.
What conditions are necessary when measuring an Eθ value?

Standard conditions are necessary when measuring an Eθ value. Standard conditions are:

  • All concentrations at 1.00moldm-3
  • Temperature of 298K
  • Pressure of 1 atmosphere
  • (Standard hydrogen electrode as one of the half cells)

Q1) What do two half-cells put together form?

Q2) How can the cell voltage be calculated?

A1) Two half-cells put together form an electrochemical cell.

A2) The cell voltage of an elctrochemical cell can be calculated by finding the difference between the standard electrode potentials of the 2 half cells

OR

Mrs Wheeler’s way: Line up the half equations the ;right way;, changing the E; values sign accordingly. Then add the two E; values together to;obtain ;E;.

For a particular redox reaction to occur, must the standard electrode potential of the half-equation involving the species;being reduced be more or less positive than the standard electrode potential of the half-equation involving the species being oxidised?
For a particular redox reaction to occur, the standard elctrode potential of the half-equation involving the species being reduced (oxidising agent) must be more positive than the standard electrode potential of the half-equation involving the species being oxidised.
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