14: Redox II
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What is the reactivity series?
Potassium (K) Sodium (Na) Calcium (Ca) Magnesium (Mg) Aluminium (Al) Carbon (C) Zinc (Zn) Iron (Fe) Tin (Pb) Hydrogen (H) Copper (Cu) Silver (Ag) Gold (Au)
In the reactivity series, what happens as you go up?
Reactivity increases, electrons are lost more easily
What is standard electrode potential (E°)?
The potential of a half-cell compared to the standard hydrogen electrode (SHE) under standard conditions
What are the standard conditions?
• 298K (25°C) • 100kPa • 1.00 mol dm-3 ion concentration
How are electrode potentials (E°) measured?
By connecting a half-cell to the SHE using a salt bridge and voltmeter
What are the two different types of half-cell?
Metal/ion half-cell Ion/ion half-cell
What is a metal/ion half-cell?
Metal in a solution of its own ions
What is an ion/ion half-cell?
Platinum electrode with two ions of the same element
What do electrode potentials tell us?
How easily a species can be reduced or oxidised
What does a more positive electrode potential mean?
The species is more likely to gain electrons (be reduced)
What does a more negative electrode potential mean?
The species is more likely to lose electrons (be oxidised)
How are simple half-cells made?
A metal solid placed in a solution that contains ions of the metal. - the metal solid is called the electrode - the solution is called an electrolyte
What are the conditions the SHE is in?
• hydrogen gas at 100kPa • bubbled over a platinum electrode • 1.00 mol dm-3 H+ solution • 298K (25°C)
What is the definition of the Standard Electrode Potential (E°)?
The measurement of the tendency of a species to gain electrons under standard conditions. It is always measured relative the SHE which is an assigned a potential of 0.00V
What does a more positive E° indicate?
A greater tendency to be reduced
What happens when you increase the concentration of the oxidised species over standard conditions?
E becomes more positive
What happens when you increase the concentration of the reduced species over standard conditions?
E becomes more negative
How do you calculate the standard cell potential?
E°cell = E°(cathode) - E°(anode) or E°cell = E°(reduction) - E°(oxidation)
What is the less negative (or more positive) electrode called?
Cathode
What is the more negative electrode called?
Anode
Which direction do electrons flow?
From the anode to the cathide
What does it mean if the E° cell value is positive?
The forward reaction is feasible
What does it mean if the E° cell value is negative?
The reverse reaction is favoured
What does a higher E° value mean?
A stronger oxidising agent