electrode potentials Flashcards
what’s a strip of metal dipped in a solution of its own ions called
electrode
or
half cell
when a strip of metal is dipped in a solution of its own ions which has a postive charge and which has a negative charge
the ions dissolve in the solution giving it a positive charge
the electrons collect on the metal giving it a negative charge
this means a potential difference is established between the too
if there is a large voltage where does the equilibrium lie
right
how do you connect two half cells
the two metal rods connected by a high resistance voltmeter
the two beakers of electrolyte are connected with a salt bridge to complete the circuit
why is pottasium nitrate a suitable solution for a salt bridge
it’s in reactive and the ions are free to move
where will the electrodes try to flow to
from the most reactive metal (left electrode) to the least reactive metal (right electrode)
what does a voltmeter do
prevents electrons flowing enabling a voltage to be measured
what would happen if a voltmeter is replaced with an ammeter or a bulb
electrons can flow and a current is produced
why might the current produced by a cell fall to zero after some time
all the reactants are used up
what will happen to a cell once the reactants are used up
stops working or starts to leak
when is a platinum electrode used
when there is no sold metal in the reaction
such as when there are metal ions of two difffent charged in the same solution
eg Fe2+ and Fe3+
in this case a metal rod made from another in unreactive metal is needed to connect the circuit so platinum is used
why is platinum a suitable electrode
it’s unreactive and conducts electricity
describe conditions of a standard electrode
H2 gas is pumped in at a pressure of 100kPa
the electrolyte contains H+ ions of concentration 1moldm^-3
platinum electrode
whole system at a temp of 298K
what is the voltage of a standard hydrogen half cell
0
all electrodes equations are shown as …..
reductions
the standard electrode potential of cu^2+/Cu is 0.37V why might the electrode potential of the following cell not be 0.37v
the concentration of the CuSO4 solution is not 1 mol dm^-3
what is being oxsidised and reduced in this convential cell representation
ROOR
the right electrode is the ……… electrode
postive
the right electrode has a more …….. standard electrode potential then the left electrode
postive
the left electrode is the …….. electrode
negative
what do vertical solid lines indicate in a convential cell representation
phase boundaries
what does a double vertical line in the middle of a convential cell representation represent
salt bridge
the species with the …….. oxidation state should be written closest to the salt bridge
highest
draw the cell representation of the standard hydrogen half cell
the standard hydrogen electrode is always written on the …..
left
all the species on the left of the arrow are ……..
oxidising agents
as the can only gain electrons
which is the most strongest oxidising agent
top left of the table with most positive standard electrode potential
if the table is +ve
⬇️
-ve
then you can use sowr
strongest oxidising agent top left
weakest reducing agent top right
equations for working out voltage of a cell
Ecell = more positive - least postive
what does it mean if an E cell value is postive
reaction is feasible and the cell discharges - produces a current
how do you recharge a cell
if a reaction is reversible you can charge it by plugging it in the mains and the reverse reaction will occur.
give an environmental advantage of using rechargeable cells
metals are reused
give an environmental disadvantage of using rechargeable cells
mains electricity is used to recharge which may come from combusting fossil fuels which realises CO2
why are conditions important in Ecells
shift equilibrium changing electrode potentials affecting Ecell values
meaning some reactions are feasible under some conditions and not others
in which direction would the electrons flow in this cell why ?
from right to left
the Cu2+ is more concentrated on the left so reduction on Cu2+ is more likely to happen on the left
the left electrode is the postive electrode so the right is the negative electrode
what kind of reaction do single use batteries have in them
irreversible
how do fuel cells create a voltage
uses energy from reaction of a fuel with oxygen to create a voltage
how would you provide a constant voltage in a fuel cell
continuously provide fuel and oxidant
what fuel do fuel cells use name 3
methanol
natural gas
petrol
name advantages of using fuel cells for energy instead of fossils fuels
greater efficiency then burning hydrogen in a combustion engine
less polluting as water is the only product
disadvantages of using fuel cells for energy instead of fossil fuels
H2 is difficult to store
fossil fuels are combusted to produce the hydrogen which releases carbon dioxide
advantages of fuel cells compared to other types of cell
voltage is constant as fuel and oxygen is supplied constantly so concentrations of reactants remain constant
