A - Electrode Potentials Flashcards
How is a simple electrochemical cell made?
From two different metals dipped in salt solutions of their own ions, connect by a wire (the external circuit).
A voltmeter is located in the external circuit.
The solutions are connected by a salt broche which allows ions to flow through.
What is the simplest form of salt bridge?
Filter paper soaked in potassium nitrate solution - KNO3(aq).
What type of reactions occur in an electrochemical cell?
Redox reactions, one oxidation and one reduction reaction.
What is an electrode?
What is another name for an electrode?
A rod of metal dipped into a solution of its own ions.
Also called a half-cell.
If you could measure the potential of a half-cell, what would it tell you?
How readily electrons are released by the metal, that is, how good a reducing agent the metal is.
Can electrical potential be measured directly?
If not, what is measured instead?
No it cannot.
Potential difference (voltage).
Why is a salt bridge used rather than a wire?
Because a wire only transfers electrons, whereas a salt bridge transfers ions.
How do electrons flow in an electrochemical cell?
From the more reactive metal to the less reactive metal through the external circuit.
What is EMF?
Electromotive force (the cell potential) - shows the voltage between the two half-cells.
What is unique about a platinum electrode?
It’s an inert metal so won’t react with the ions.
What are electrode potentials measured against?
The standard hydrogen electrode.
What conditions can affect the cell potential?
Temperature, pressure and concentration.
Define the standard electrode potential of a half-cell.
The voltage measured under standard conditions when the half-cell is connected to a standard hydrogen electrode.
What are the standard conditions for the standard hydrogen electrode?
- Any solutions must have a concentration of 1.00 mol dm-3.
- Temperature must be 298 K.
- Pressure must be 100 kPa.
If standard conditions are maintained, what will the reading on the voltmeter be when the half-cell is connected to the standard hydrogen electrode?
The standard electrode potential of that half-cell.
Describe the standard hydrogen electrode.
Hydrogen gas is bubbled into a solution of H+ (aq) ions.
Since hydrogen doesn’t conduct, electrical contact is made via a piece of unreactive platinum metal (coated with finely divided platinum to increase the surface area and allow any reaction to proceed rapidly).
The electrode is under standard conditions.
What is the potential of the standard hydrogen electrode defined as?
0.
What must the salt chosen for the salt bridge not do?
It must not react with either of the solutions in the half cells.
What reactions occur at the negative and positive electrodes.
Oxidation occurs at the negative electrode.
Reduction occurs at the positive electrode.
What is an electrochemical series?
A list of standard electrode potentials for different electrochemical half-cells.
What do more positive electrode potentials mean in an electrochemical series?
- The left-hand substances are more easily reduced.
2. The right-hand substances are more stable.
What do more negative electrode potentials on and electrochemical series mean?
- The right-hand substances are more easily oxidised.
2. The left-hand substances are more stable.
What can you calculate using standard electrode potentials?
What formula allows you to do this?
The standard cell potential (EMF) when two half-cells are joined together.
EMF(cell) = EMF(reduced) - EMF(oxidised)
What directions will the equilibrium equations go in for a half-cell that has a more negative electrode potential, and one that has a more positive electrode potential?
The half equation for a more negative electrode potential will go in the direction of oxidation.
The half equation for a more positive electrode potential will go in the direction of reduction.