Electrode Potentials Flashcards
Which metal is more reactive, copper or zinc?
zinc
What is the reactivity series?
K, Na, Li, Ca, Mg, Al, Zn, Fe, Cu, Ag, Au
What would happen in the reaction between copper sulphate (III) and zinc
Zn metal would disappear
Cu metal would ppt out of solution
Blue colour of Cu2+ would disappear and colourless solution would form
Would there be a reaction between zinc (II) sulphate and copper?
No, this reaction would not take place. Zn2+ is not reactive enough (a powerful enough oxidising reagent) to remove the electrons from Cu metal.
what is a cell?
An electrochemical cell, or voltaic cell, allows the transfer of electrons to be
‘captured’ in an electrical circu
Why do electrons flow from left to right in a cell built from the reaction of copper (II) sulphate and zinc
zinc electrode is more negative than the copper and so electrons flow from
left to right on this diagram.
What are the types of half cell?
Metal Electrode & Metal Ions
Platinum Electrode & Metal Ions
Platinum Electrode, Ions in acid solution
Platinum Electrode & Gas System
When labelling the gas on a pt electrode and gas system, what must I include?
gas pressure
What is an example of metal electrode and metal ions?
Fe2+ + 2 e− → Fe
What is an example of pt electrode and metal ions?
Fe3+ + e− → Fe2+
What is an example of pt electrode, ions in acidic solution?
MnO4− + 8 H+ + 2 e− → Mn2+ + 4 H2O
What is an example of Platinum Electrode & Gas System?
Cl2 + 2e− → 2Cl−
What does a half cell represent?
represents the half-equation in a redox reaction
what does a full cell represent?
A cell, the combination of
two half-cells, represent the full redox reaction.
What is ONE ROPE?
-oxidation positive electrode
-reduction on negative electrode
What does the standard hydrogen electrode do?
standard allows measurement of the oxidising or reducing ability of each
different system
What is happening at the standard hydrogen electrode?
As the hydrogen gas flows over the porous platinum, an equilibrium is
set up between hydrogen molecules and hydrogen ions in solution.
Platinum provides a surface for this reaction to happen
What are the standard conditions for the standard hydrogen electrode?
-The position of any equilibrium can be changed by changing conditions. That means that the conditions must be standardised so that you can make fair comparisons.
• The gas pressure is 100 kPa
• The temperature is 298 K (25°C).
• All ions concentrations are taken as being 1 mol dm−3
when are pt electrodes used?
when you cannot make an electrode (an electrically conducting solid) out of one of the species involved in the half equation
What is the salt bridge includes to do?
– to complete the electrical circuit, without introducing any more metal into the system.
what does a salt bridge look like?
It is a glass tube filled with an electrolyte like potassium nitrate solution (usually more of a paste).
why are the ends of a salt bridge stoppers by bits of cotton wool?
stops too much mixing of the contents of the salt bridge with the contents
of the two beakers.
how is the electrolyte in a salt bridge chosen?
The electrolyte in the salt bridge is chosen so that it does not react with
the contents of either beaker. This allows a beaker to remain neutral.
What is standard electrode potential?
The voltage measured when the named electrode is connected to the standard hydrogen electrode, at 298 K under 100 kPa with solutions of 1.00 moldm−3.
What do cells and half cells respond to?
are at equilibria and respond to le Chatelier’s principle- Decreasing the concentration of a species on the left-hand side of the reduction half-equation will make the electrode potential less positive
What must I know?
• For metals and their ions, the metal is the electrode
• For non-metals that are gases, we use the half-cell for gases with a platinum
electrode
• For ions of the same element we use a mixture of the ions (sometimes in acidic
conditions) in the same beaker, at standard concentrations, with a platinum
electrode.
What does a more the positive value mean?
the more likely that reaction is to go from left to right,
What does the more negative the value mean?
more likely it is to go from right to left.
a
where is the strongest oxidising agent found?
on the LHS of the most +ve SEP half equation.
where is the strongest oxidising agent found?
The strongest reducing agent is found on the RHS of the most -ve SEP half equation
What way will the equilibrium with the more negative E value move?
to the left
What way will the equilibrium with the more positive E value move?
right
how can we work out the cell reaction and cell potential?
by:
• more positive - less positive
• adding the two standard electrode potentials
• work out the overall reaction by combining the two half equations.
what role doesn’t apply when working out if a reaction is feasible?
more positive take less negative
If a reaction is found to be feasible, why does it not necessarily mean that the reaction takes place?
-some reactions have a very large activation energy and therefore there will be a very slow rate of reaction.
–the calculations above are based on data obtained under standard conditions. If, for example, the concentration of a reactant is not 1
moldm−3, then the half-cell potential will be different. Also, some reactions do not
take place in aqueous solutions and may need a solvent that is not water.
(check notes) x 2
How do you know which is the strongest reducing agent?
• Eθ for forward reaction is least positive
• Reverse reaction (oxidation) more likely to occur
why does is cobalt (III) more stable in ammonia than in water?
• Ammonia is a stronger ligand than water
• Ammonia is a stronger base
• Ammonia can donate its lone pair more easily.
how do you measure a standard cell potential?
-Prepare two standard half cells. Think about the contents of each half cell –
reacting ions should have concentrations of 1 moldm−3, gases pressures of 100 kPa,
temperature should be 298K. Do you need a platinum electrode?
-Connect the electrodes of the half cells to a voltmeter using wires.
-Prepare a salt bridge by soaking a piece of filter paper in aqueous KNO3.
-Connect the two solutions of the half cells with a salt bridge.
-Record the standard cell potential from the voltmeter.
when does the overall equation of an electrochemicals occur?
when the cell is discharging
What are single use cells sometimes called?
primary cells
what are cells that can be recharged sometimes called?
Secondary cells
what happens when a rechargeable battery is charging?
voltage is applied to reverse any
chemical change that has taken place whilst the battery was discharging. This is called charging or recharging
what is the definition of a fuel cell?
A fuel cell uses the energy generated from the reaction between a fuel
and oxygen to create a voltage.
(check notes)
