electrode potential and cells Flashcards
what are the three type of cells
metal/metal ion
non metal/non metal
metal ion/metal ion
what is a half cell
compromises of an element in two oxidation states
what is in the simplest half cell
has a metal placed in an aqueous solution of its ions
where is the equilibrium
on the surface if the metal between the different oxidation state of the metals
how is the equilibrium written
in reduction form with the electrons always on the left
what happens if the equilibrium lies on the left
more electrons are released
more negative electrode
more oxidation
what happens if the equilibrium lies on the right
more electrons are gained
more reduction
more positive
how is e cell value calculated
obtained by comparing a cell to the standard hydrogen electrode she
what is the units for the e cell
volts
what is the she
it is a standard reference used as a comparison tool to compare potential to that of the she
what does the she have a potential of
o.oo v
describe the conditions of a standard hydrogen electrode
hydrogen gas bubbles
1mol/dm3
29k
100kpa
how is the platinum structured
coated with finely divided platinum which as a conducting surface
why is platinum used
it is unreactive and inert so doesn’t make a potential difference but also conducts electricity
what are properties of platinum
it is porous so it can absorb hydrogen gas
what exists on the surface of platinum
an equilibrium between hydrogen and hydrogen ions
why is standard conditions required
otherwise the position of redox equilibroium will change with conditions
how else can half cells be made
by two aqeous ions of the same element for example fe2+ and fe3+
what must be ensure
that the concentration of both ions are 1mol/dm
what is used as the conducting surface
platinum and metal surface
what is an electrochemical cell
it is formed from one half cell that releases electron and one half cell that gains electrons
what are connected to the half cells
a wire and a salt bridge
what does a wire allow
allows electrons to be transferred between the two half cells
what does the salt bridge provide
an electrical connection between the two solutionsq
what does this allow
ions to move through it and complete the circuit
how is a salt bridge made
using filter paper soaked in aqueous solution of ionic compound
what must the ionic compound be and give an example
react with either half cell solution or electrodes so kno3 or nh4no3
why will sodium chloride not be suitable for a salt bridge of a cell
as the cl- will react with some metal ions to form complexes / precipitates
why would a wire not be a suitable salt bridge
a wire would set up its own electrode system with the solution
where is the voltmeter found
between two half cells
what must the voltmeter be and why
a very high resistance to stop the current from flowing through the circuit
what does this allow
the maximum potential difference can be measured
what happens to the reaction when there is a high resistance
no reaction takes place as the current stopped from flowing
what happens if the voltmeter is replaced by a bulb
a current flows
what happens to this current
it lead to reactions occurring separately at each electrode
what will happen to the voltage
it will fall to zero as the reactant concentration decreased and become the same at each electrode
HOW DO WE DRAW THE CELL
the more negative half cell is always on the right ROOR
