1.11 - Electrode Potentials and Cells Flashcards
What happens when a rod of a metal is dipped into a solution of its own?
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?
To 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 in standard cell notation?
The most reduced one.
What does | indicate?
Phase boundary (s,l,g)
How would an Aluminium/Copper 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 hand electrode 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 value? What happens to the metal with the most negative E value?
Oxidation - left hand electrode
What conditions are required for SHE?
Temp = 298K
Pressure = 100kPa
[H+] = 1.00 moldm-3
What is the SHE used for?
Comparing other cells
E value of SHE is defined as 0, so all the E values are compared against it.
Why might you use standard electrodes occasionally?
- The 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 so it is easier to oxidise.
If an E value is more positive, what does it mean in terms of oxidising/ reducing power?
Better oxidising agent so it is easier to oxidise.
What factors will change E values?
Concentration of ions
Temperature
What happens if you reducd the concentration of the ions in the left hand half cell?
Equilibrium moves to the left to oppose the change of removing ions; this releases more electrons, the E of the left hanf cell becomes more negative, so e.m.f of the cell increases
How do you calculate the emf of a cell from E values?
Ecell = right - left
When would you use a platinum electrode?
When both the oxidised and reduced forms of the metal are in aqueous solution
Why is platinum chosen?
Its inert so it does not need to take part in the electrochemistry. It is also a good conductor to complete the circuit.
