20 - Electrode Potentials And Electrochemical Cells Flashcards
What is a half cell?
When a rod of metal is dipped into a solution of its own ions, setting up an equilibrium.
What is an electrical cell?
A system that consists of two half-cells, each with a different electrode potential, connected by a salt bridge.
What is a salt bridge?
A solution that enables ions to flow between half cells connected in a circuit.
What solution is typically used for a salt bridge?
Potassium nitrate
What is the simplest form of a salt bridge?
Filter paper soaked in a solution of a salt.
What do you need to consider when picking a salt for a salt bridge?
The salt must no react with either of the half cell solutions.
What determines a metals ability as a reducing agent?
The more readily electrons are released by the metal the better its ability as a reducing agent.
What is a standard hydrogen electrode used for?
Used to compare the tendency of different metals to release electrons, as the potential of it is defined as zero so the measured voltage when connected to another half cell is that cells electrode potential.
How does a standard hydrogen electrode work?
Hydrogen gas is bubbled into a solution of H+ ions and electrical contact is made via a block of unreactive platinum black, as hydrogen doesn’t conduct, then acts as a half cell.
What does the electrode potential of a cell tell us?
Electrodes with more negative electrode potentials are better at releasing electrons.
What is the electrochemical series?
A list of some electrode potential values for different metals.
What does a single line | mean when representing half cells?
Phase boundry
What does a double line || mean when representing half cells?
Salt bridge
When representing half cells which side does the cell with the most negative potential go?
Left side
When representing half cells which species go closest to the salt bridge?
Species with the highest oxidation state.
What is the formula for emf?
E°(Right) - E°(Left)
What does the overall emf tell us about the reaction?
If the overall emf is positive the reaction taking place is feasible/ favourable.
How do you know which way electrons flow in an electrical cell?
They flow from the more negative electrode to the more positive electrode.
What’s the relation with with emf and entropy?
A positive emf change will have an overall positive entropy change.
What’s important to remember about a positive emf?
It indicates that a reaction is thermodynamically feasible but it may not be kinetically feasible.
How does a zinc/copper cell work?
Works on the principle of electrons being transferred from a more reactive metal to a less reactive.
How does a zinc/carbon cell work?
Anode - zinc canister
Cathode - central carbon rod
Electrolyte - paste of ammonium chloride
Which is surrounded with a mixture of manganese oxide and powdered carbon.
How does an alkaline cell work?
Anode - powdered zinc
Cathode - magnesium dioxide
Electrolyte - potassium hydroxide
