What is a salt bridge?
this is a piece of filter paper soaked in potassium nitrate solution.
Its purpose is to complete the circuit and to replace cations and anions that leave the solution
what is an electromotive force (e.m.f) value?
this is the difference between electrode potential between the two metals (electrodes)
what is the standard electrode potential (SHE) of a standard half cell?
this is the voltage of that half cell relative to a standard hydrogen half-cell under standard conditions
what is the standard cell potential?
this is the voltage developed under standard conditions when two standard half cells are joined
what does the standard hydrogen electrode consist of?
this consists of
- H2 gas at 1 atm and 25°C bubbling on a platinised platinum electrode
- the electrode is immersed in 1moldm-3 solution of H+ ions
draw the standard hydrogen electrode.
no, you actually have to do this. It’s a question that comes. It’s really easy to learn. (see page 184)
what are the functions of the platinum electrode in the standard hydrogen electrode?
- it acts as an inert connection to the H2/H+ system. This means that it doesnt try to form ions with itself because it is unreactive
- It allows H2 gas to be aDsorbed (not aBsorbed) onto its surface .
- It is platinised which increases surface area which results in increased reaction rate
what is the difference between the terms ‘absorbed’ and ‘adsorbed’?
aBsorbed- occurs when a liquid actually soaks into a medium
aDsorbed- occurs when a liquid just accumulates on a surface without soaking into it.
what is the standard electrode potential of the platinum half cell?
0
how can the standard electrode potential of a species be obtained?
what criteria must be met for this to occcur?
this species can be connected to the standard hydrogen half cell
- all solutions must have a concentration of 1moldm-3
- temperature must be 25°C
- any gases involved must have a pressure of 1atm
- platinum must be used as an electrode when the half cell system does not include a metal
what are fuel cells?
where are they found?
what are they made of?
- fuel cells are electrochemical cells which convert chemical energy of a fuel to electrical energy
- fuel cells can be found in vehicles. they produce electricity which is used to power the motor of a car
- fuel cells are made up of a cathode, an anode and an electrolyte. the electrolyte consists of warm KOH solution which contain K+ and OH- ions (from KOH) and H+ and OH_ ions (from H2O)
what happens at the anode of a fuel cell?
H2 gas enters at the anode and splits into H+ and electrons.
The electrons flow through an external circuit which generates a current
- The H+ stays in the KOH solution and combines with the OH- forming water
Overall equation is H2 + 2OH- = 2H2O +2e
what happens at the cathode of a fuel cell?
O2 gas enters at the cathode.
It combines with water and electrons to form OH-
overall equation is )2(g) + 2H2O(aq) = 2H2O + 2e
state some advantages of fuel cells
- pollution free
- they convert 70% of chemical energy into electrical energy. (they are efficient)
(BONUS) they provide water, heat and electricity to astronauts
state one disadvantage of fuel cells
- catalysts in fuel cells are rapidly poisoned
state two uses of standard electrode potential
- predict the feasibility of a reaction
- calculate the standard cell potential
