Electrode Potentials and Cells Flashcards
why do electrochemical cells use redox reactions?
the e- transfer between products creates a flow of electrons.
what is an electrical current
the flow of e-
what is produced between the 2 electrodes
a potential difference which can be measured
draw a cell diagram
2x solutions
2 electrodes
salt bridge
voltmeter
what is a salt bridge
used to connect the circuit
allows the flow of ions - free moving ions conduct charge
what is a salt bridge made of
from a piece of filter paper soaked in a salt solution - usually potassium nitrate
the salt should be…
unreactive with the electrodes and electrode solutions
why would potassium chloride not be suitable for copper systems
chloride ions will react and form complexes with copper ions
why is a wire not used for the salt bridge
the metal wire would set up its own electrode system with the solutions
what do simple half cells consist of
metal - the electrode
and a solution of a compound containing the metal e.g. Cu and CuSO4
what do the half cells do when connected to a circuit
produce a small voltage - becomes a battery/ cell
what is the p.d (E) measured with
a high resistance voltmeter
why use a high resistance voltmeter
stops current from flowing into circuit
allows for it to be possible to measure the max possible p.d
the reactions won’t occur because the very high resistance voltmeter stops the current from flowing
what happens if current is allowed to flow
reactions occur separately at each electrode
which electrode always undergoes REDUCTION
POSITIVE electrode
Cu2+ + 2e- –> Cu
which electrode always undergoes OXIDATION
NEGATIVE ELECTRODE
Zn –> Zn2+ + 2e-
what does a solid vertical line represent in a cell diagram
phase boundary (between electrode and electrolyte)
what does the double line represent
salt bridge
what is put next to the double line
the most oxidised form, e.g. Zn2+
what is written on the right
the more positive half cell if possible
what do u use if there is a system which has no metals
a platinum electrode must be used
what does a platinum electrode do
provides a conducting surface for e- transfer
why is a Platinum electrode used
unreactive + conducts electricity
example where Pt electrode can be used
Fe2+ –> Fe3+ + e-
II Fe3+(aq), Fe2+(aq) IPt
