Electrochemical Cells Flashcards
(28 cards)
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-
What is the simplest salt bridge made of
Filter paper soaked in saturated solution of KNO3
Why are salt bridges necessary
They 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
II
What type of species goes on the outside in standard cell notation
The most reduced species
What does I indicate
Phase boundary
What happens at the left side electrode
Is where oxidation occurs
Half cell with mist negative E nought value
What happens at the right hand electrode
Reduction occurs
Half cell with most positive E nought value
What conditions is the SHE used in
Temperature = 298 K Pressure = 100 kPa [H+] = 1.00 mil dm-3
What is SHE used for
Comparing other cells against
E nought value is 0
Why might you use other standard electrodes occasionally
Cheaper
Easier
Quicker
Platinum is expensive
What factors will change E nought values
Concentration of ions
Temperature
What happens if you reduce the concentration of the ions in the left hand side cell
Equilibrium moves to the left to oppose the change
This release more electrons
So E nought value becomes more negative
So EMF increases
How do you calculate the EMF of a cell from E nought values
E nought of the right - E nought of the 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
Inert is does not take part in the electrochemistry
Good conductor to complete the circuit
How would you predict if a reaction would occur
Find the species being reduced, calculate its E nought value
Calculate the E nought value of the species being oxidised
Reduction - oxidation
If E nought value > 0 then the reaction will occur
What are zinc/carbon cells more commonly known as
Disposable batteries
What are the two reactions that take place in zinc/carbon cells
Zn oxidised to Zn2+
NH4+ reduces to NH3 at carbon electrode
What are the reactions that occur in a lead/acid battery
Pb + SO42- -> PbSO4 + 2e-
PbO2 + 4H+ + SO42- + 2e- -> PbSO4 + 2H2O
How are cells recharged
Reactions are reversible and are reversed by running a higher voltage through the cell than the cell’s E nought
Where are lithium ion cells used
Mobile phones
Laptops
What is a fuel cell
A cell that is used to generate electric current
Does not require electrical recharging
