Electrode potentials and electrochemical cells
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What happens when a rod of a metal is dipped into a solution of its own ions
An equilibrium is set up between the solid metal and the aqueous metal ions
Write a half-equation for zinc (s) to zinc (II)
Zn (s) ⇋ Zn2+ (aq) + 2e-
Write a half-equation for copper (II) to copper (III)
Cu2+ (aq) ⇋ Cu3+ (aq) +e-
What is the simplest salt bridge made of?
Filter paper soaked in saturated solution of KNO3 (potassium nitrate)
Why are salt bridges necessary
Complete the circuit, but avoid further metal/ion potentials as does not perform electrochemistry Allows ion movement to balance the charge. Do not react with electrodes
What symbol is used to represent a salt bridge in standard notation
||
What type of species goes on the outside (furthest from the salt bridge) in standard cell notation
The most reduced species
What does | indicate?
Phase boundary (Solid/liquid/gas)
How would an Aluminium/Copper cell be represented?
Al (s) | Al3+ (aq) || Cu2+ (aq) | Cu (s)
What happens at the left-hand electrode
Left hand electrode is where oxidation occurs Left hand electrode is the half cell with the most negative E* value
What happens at the right-hand electrode
Right electron is where reduction occurs Right hand electrode is the half cell with the most positive E* value
Which side of the cell has the most negative E* value? What happens to the metal with the most negative E* value?
Left hand electrode - Oxidation
What conditions is the standard hydrogen electrode used in?
Temperature = 298K Pressure = 100kPa [H+] = 1.00 mol dm-3
What is the standard hydrogen electrode used for?
Comparing other cells against. E* of SHE is defined as 0, so all E* values are compared against it
Why might you use other standard electrodes occaisionally
They are cheaper/easier/quicker to use and can provide just as good a reference Platinum is expensive
If an E* value is more negative, what does it mean in terms of oxidising / reducing power?
Better reducing agent (easier to oxidise)
If an E* value is more positive, what does it mean in terms of oxidising/reducing power?
Better oxidising agent (easier to reduce)
What factors will change E* values
Concentration of ions Temperature
What happens if you reduce the concentration of the ions in the left hand half cell
Equilibrium moves to the left to oppose the change of removing ions; the releases more electrons, the E* of the left hand cell becomes more negative, so the e.m.f. of the cell increases