11: Electrochemical cells and electrode potentials Flashcards
What is the connection between the two solutions called
The salt bridge
What is the purpose of a salt bridge
Allows movement of ions between the two solutions
No electrons are transferred through the salt bridge
How can a simple salt bridge be made
Piece of filter paper soaked in saturated potassium nitrate solution
Which electrode does reduction happen at
Positive electrode
Reduction
At
Positive
Which electrode does oxidation happen at
The negative electrode
What is the potential difference measured in the cell called
Cell potential
What is used when an electrode cant be made (i.e.. the half cell reaction is only between gases and/or aq)
Platinum
How does a standard hydrogen electrode work
Hydrogen gas is bubbled over a platinum electrode. The platinum is almost entirely unreactive so does not interfere with the chemistry, but conducts the electrons and forms a catalytic surface on which the hydrogen gas can be in contact with the hydrogen ions.
What is the half equation for the hydrogen electrode
H†(aq) + e¯ ⇌ ½H₂(g)
What are standard conditions for any half cell
Temperature: 298K (25℃)
Solutions at 1.00 moldm¯³
Gases at 1 atmosphere pressure
What is the standard electrode potential (Eϴ) of a half cell
The voltage measured in a cell in which that half cell is connected to a standard hydrogen electrode, under standard conditions
What does a very positive Eϴ mean
Reduction will occur readily at the electrode
What does a very negative Eϴ mean
Oxidation occurs readily at this electrode
How does a metal’s reactivity affect its Eϴ
The more reactive a metal is, the less favourable reduction of its ions will be and the more negative the Eϴ will be
How set up half cell for gases and ions
Bubble gas over platinum electrode and immerse it in a solution of the ions formed by the oxidation or reduction of the gas
How to set up half cell for ions in solution
submerge platinum electrode in solution containing the ions
What is standard cell potential (Eϴ cell)
It is equal to the difference between the Eϴ values
Always expressed as a positive value
How do you know which half reaction will oxidise and which will reduce
The half reaction with the more positive value for Eϴ will reduce
How can you work out what effect a change in conditions will have on electrode potentials
Using Le Chatelier’s principles
What happens to the electrode potential in the half cell Zn²†(aq) + 2e¯ ⇌ Zn(s) when the concentration of Zn²† is increased
The equilibrium will move to the right to compensate so reduction is now favoured so the electrode potential will become more positive
How close do the Eϴ values have to be so that when it is not standard conditions, you can not reliably predict the direction of reaction
Within about 0.3V
What is a storage cell
An electrochemical cell where the voltmeter can be replaced by an electrically powered device (e.g. a light bulb) and energy released by the cell reaction is used to create a voltage for the device
What is a fuel cell
An electrochemical cell which uses the energy released by the reaction of a fuel with oxygen to generate a voltage
How does a fuel cell differ from a storage cell
It is not a closed system
How does a fuel cell work
A continuous supply of fuel (such as hydrogen or an organic compound) is delivered to the negative electrode to be oxidised whilst a continuous supply of oxygen (usually air) is delivered to the positive electrode to be reduced
