1.11 Electrode potential and cells Flashcards
Write a half equation for zinc s to zinc ion
Zn(s) <–>Zn2+(aq) + 2e-
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. Dont 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 saltbridge) 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 cell 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 cell value
Which side of the cell has the most negative e cell value? what happens to the metal with the most negative e cell value
Oxidation - left hand electrode
What conditions is the standard hydrogen electrode used in
Temp = 298K
Pressure = 100kPa
[H+] = 1.00 moldm-3 (conc)
What is the standard hydrogen electrode used for
Comparing other cells against
E cell of SHE is defined as 0 so all other E cell values are compared against it
Why might you use other standard hydrogen electrodes occasionally
Cheaper/easier/quicker to use
Platinum is expensive
If E cell is more negative what does it mean in terms of oxidising/reducing power
Better reducing agent (easier to oxidise)
If e cell is more positive what does it mean in terms of oxidising/reducing power
Better oxidising agent (easier to reduce)
What factors will change e cell values
Conc of ions
Temperature
What happens if you reduce the conc of ions in left hand half cell
Eqm moves to left to oppose change of removing ions; releases more electrons, e cell of LH cell becomes more negative so e.m.f of cell increases
How to calculate emf of a cell from e cell
E cell = E right - E left
When would you use a platinum electrode
When both the oxidised and reduced forms of the metal are in aqueous solution
What are zinc/carbon cells more commonly known as
Disposable batteries
What are the 2 reactions that take place in zinc/carbon cells
Zn oxidised to Zn2+
NH4 + reduced to NH3 at carbon electrode
How are cells recharged
Reactions are reversible and are reversed by running a higher voltage through the cell then the cells E cell
Where are lithium ion cells used
Mobile phones
Laptops
What is a fuel cell
A cell that is used to generate electric current; doesnt require electrical recharging
