EMF Flashcards
what is electrode potential a measure of?
oxidising ability
what does a high and positive electrode potential mean?
very good oxidising agent
what is the emf of a standard hydrogen electrode?
0
why is the emf of the she 0?
acts as a baseline - used as a comparison
how should the standard hydrogen electrode and the other half cell be connected?
with a high resistance voltmeter and a salt bridge
how can you make a salt bridge?
soak filter paper in potassium chloride/nitrate
fill a u tube with KCl in agar jelly
what is the purpose of a salt bridge?
completes the circuit
balances the charges
why do you stopper the end of a salt bridge with cotton wool?
to stop too much mixing of salt bridge solution with the contents of the two beakers
describe how the standard hydrogen electrode is set up
solution of H+ ions
platinum electrode (platinum foil over porous platinum)
H2 gas
what standard conditions are all half cells under?
all solutions are 1M
gases at 100kPa
298K temp
why do half cells need to be under standard conditions?
because the equilibrium shifts with a change in conditions
why is a high resistance voltmeter needed when connecting two half cells?
to avoid the flow of current because this will cause a drop in the voltage
define standard electrode potential
the electrode potential of a standard electrode with ion conc of 1M at 298K connected to a standard H electrode using a high resistance voltmeter and salt bridge
which side does the oxidation half cell go on?
the left
which side does the reduction electrode go on?
the right
what is the equation to find the EMF of a whole cell?
E(rhs)-E(lhs)
explain how electrode potentials can show the feasability of a cell?
the more positive a cell’s emf, the more feasible the reaction
which side is the SHE always on?
the left
give a commercial use of cells
commercial source of electrical energy
what are primary cells?
single use/disposable cells
what are secondary cells?
rechargeable cells
what’s an example of a non-rechargeable cell?
Zn and MnO2
advantages of non-rechargeable cells
low cost
non-toxic material
disadvantages of non-rechargeable cells
can leak
cannot be recycled
unstable
give examples of rechargeable cells
nickel cadmium
lead-acid
lithium ion
give some uses of lithium ion cells
provide electrical energy for tablets, laptops and phones
what is the purpose of graphite powder in a lithium fuel cell?
acts as a support medium
why can water not be used in a lithium fuel cell?
reacts with the lithium
give the equation of the oxidation reaction in a lithium ion cell
Li —-> Li+ + e-
give the equation of the reduction reaction in a lithium ion cel
e- + Li+ + CoO2 —> Li+[CoO2]-
give the cell notation for a lithium ion cell
Li(s)/Li+(aq) // Li+, CoO2/ Li+[CoO2]-
advantages of rechargeable cells?
reusable
prevents waste
slows depletion of metals and other reagents
less energy used to extract metals
what is a fuel cell?
a cell which converts chemical energy from a redox reaction into electrical energy (generate an electric current)
what are the main types of fuel cell?
hydrogen or ethanol
give the oxidation reaction in an acidic hydrogen fuel cell
H2(g) —-> 2H+(aq) + 2e-
give the reduction reaction in the acidic hydrogen fuel cell?
O2(g) + 4H+ + 4e- —–> 2H2O (l)
give the oxidation reaction in an alkaline hydrogen fuel cell
H2 + 2OH- —-> 2H2O
give the reduction reaction in an alkaline hydrogen fuel cell
O2 (g) + 2H2O + 4e- —-> 4OH-
what are the advantages of fuel cells?
no need to recharge them
run for as long as you supply them with fuel
steady output of voltage
doesn’t generate CO2 - only product is water
what is the advantage of using fuel cells in cars?
uses more available energy for kinetic energy so less energy is wasted as heat
what are the disadvantages of fuel cells?
not carbon neutral bc CO2 released when the methane and steam react to form hydrogen
expensive
difficult to store
flammable
