3. Redox and Electrode potential Flashcards
What is reduction?
Gain of electrons
Loss of O2
Gain of H+
What is oxidation?
Loss of electrons
Gain of O2
Loss of H+
What is a reducing agent?
A species that reduces another and is itself oxidised.
What is an oxidising agent?
A species that oxidises another and is itself reduced.
What is the purpose of the wire in a cell?
Allows electrons to flow from the half-cell where oxidation occurs to the half-cell where reduction occurs.
Why do we include a high resistance voltmeter in a cell?
To measure the potential difference of the cell.
What is the salt bridge made of?
Filter paper soaked in saturated potassium nitrate (KNO3).
What is the purpose of the salt bridge in the cell?
It allows ions to flow between the half-cells without mixing, completing the circuit.
What are the three types of electrochemical half-cells?
Metal/metal ions
A gas with a solution of non-metal ions
A solution of metal ions in two oxidation states
Describe a metal/metal ions half-cell
A piece of metal electrode with a solution of 1moldm-3 metal ions.
Describe a gas with a solution of non-metal ions half-cell
Gas is bubbled over an inert platinum electrode which is dipped in the ion solution.
Describe a solution of metal ions with two oxidation states half-cell
Inert platinum electrode dipped in the solution.
What is the metal ions with two oxidation states half-cell usually used for?
Transition metals.
What is the standard electrode potential?
The potential difference between the standard hydrogen electrode and any other system in which the concentration of the active ions in solution is 1moldm-3 and gases are at 1atm and 298K.
What is the standard hydrogen electrode?
A platinised platinum electrode which is dipped in 1moldm-3 solution of H+ ions and hydrogen gas passed over the electrode in standard states.
What is standard states?
1atm pressure, 298K and 1moldm-3 concentration.
What is the EØ value for a species that is easier to reduce?
A positive EØ value.
What is the EØ value for a species that is easier to oxidise?
A negative EØ value.
Why is hydrogen’s standard electrode potential 0.00V?
Because it is the standard to which other elements are measured against.
How to find the more positive electrode?
It has the more positive EØ value.
How do electrons flow about the cell?
They flow to the half-cell with the more positive EØ value.
What is the EMF of the cell?
The difference between the EØ values of the two half cells (always positive).
How to calculate the EMF of the cell?
Most positive EØ- most negative EØ, reduced species- oxidated species.
How to calculate feasibility of the cell?
Right hand side- left hand side (if negative, not feasible).
Describe how the hydrogen fuel cell creates electricity
The fuel cell passes the fuel over platinum metal which acts as a catalyst but also as an electrode for the electrochemical system. Electrons are removed from H2 atoms at one electrode. The protons diffuse through the semi-permeable membrane to the other electrode where they form H2O.
What is the overall reaction for the hydrogen fuel cell?
2H2 + O2 —> 2H2O
What is the overall voltage produced by the hydrogen fuel cell?
1.23V.
What are the advantages of the hydrogen fuel cell?
Only H2O produced
No heat, very efficient
Quiet and simple to produce
What are the disadvantages of the hydrogen fuel cell?
Gases are harder to store
H2 is explosive
H2 is expensive
