Redox 2
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Describe a method to set up an electrochemical cell.
• Obtain metals that are cleaned with sandpaper (to ensure impurities are removed) • wash surface of the metal with propanone and wear gloves (so no hand grease gets on the metal) • Place each metal into a solution containing the ion of the same metal • Make salt bridge from filter paper (soaked filter paper in Potassium Nitrate) • connect electrodes with Voltmeter, crocodile clips and wires to measure potential difference.
Describe 2 methods to construct a half cell
• metal dipped into a solution of its ions • or platinum electrode with 2 aqueous ions.
Describe the movement of electrons in an electrochemical cell
• flow from a more reactive to less reactive metal.
What is the function of the salt bridge?
• Ensures charges are balanced on either side of the electrochemical cells.
How can you tell which electrode is going through oxidation and which one is going through reduction?
• one with the most negative cell value is where oxidation takes place. • one with the most positive value is where reduction takes place.
What is a standard hydrogen electrode?
• a electrode that is used as a reference to measure E0 values.
What conditions must be met for a reading to show up in the voltmeter when a metal is connected to the SHE?
• standard conditions of : • 298K • 100kPa • 1moldm^-3 concentrations of ions.
How can you tell is a cell is a strong oxidising agent?
• from the left side of the equation going down in the electrochemical series. • So more likely to be reduced (to gain electrons)
How can you tell is a cell is a strong reducing agent?
• from the right hand side of the equation going up in the electrochemical series • so more likely to be oxidised (to loose electrons)
How do you calculate the standard cell potential?
• E0reduced - Eoxidised
Quicker way to tell what half cell is being oxidised and reduced
• most negative E0 value= oxidised (so best reducing agent) • most positive E0 value = reduced.(so better oxidising agent)
What factors affect half cells?
• temp • conc • pressure
What is the cell notation form?
• reduced form (electrode) I electrode (oxidised form) II Oxidised form I reduced form
How to predict if a reaction will be feasible?
• E0 calculation will have a positive value
What may cause the electrode potentials to change?
• change in concentration or temperature
What might make a reaction kinetically unfavourable?
• if the activation energy is too high • if the rate of reaction is extremely slow.
What is the link between entropy and cell potential?
• the larger the cell potential, the larger the total entropy change during the cell reaction • so E0 is proportional to ΔStotal
What is the link between entropy and the equilibrium constant?
• E0 is proportional to lnK
What is a fuel cell?
• uses the energy from the reaction of a fuel with oxygen to create a voltage
Give the half equation for the reaction at the anode in a fuel cell
2H2 + 4OH- —> 4H20 + 4e-