Electrode potential and Cells Flashcards
How can you make an electrochemical cell?
An electrochemical cell can be made from two different metals dipped in salt solutions of their own ions and connected by a wire.
What is a salt bridge?
The solutions in an electrochemical cell are connected by a salt bridge made from filter paper soaked in KNO3. This allows ions to flow through and balance out the charges.
What is the EMF and how do you measure it?
You could put a voltmeter in the external circuit to measure the voltage between the two half-cells. This is the EMF (electromotive force)
Why are electrodes sometimes made of platinum?
The electrode is made of platinum because it is an inert metal, so it won’t react with the ions.
What is the standard electrode potential?
The standard electrode potential of a half cell is the voltage measured under standard conditions when the half cell is connected to a standard hydrogen electrode.
What are standard conditions?
- any solutions must have a concentration of 1 mol dm3
- the temperature must be 298k
- the pressure must be 100kpa
How do you work out the standard electrode potential?
E cell = E reduced - E oxidised
What are some of the important conventions needed when drawing electrochemical cells?
- the half cell with the more negative potential goes on the left
- the oxidized forms go in the center of the cell diagram
How would you use electrode potentials to predict whether a reaction will happen?
For any feasible reaction the E cell is positive
What are batteries?
Batteries are a type of electrochemical cell that provide the electricity we use to power things like watches and mobile phones. Some types of cells are rechargeable while others can only be used until they run out.
What are non-rechargeable batteries?
Non-rechargeable batteries are cheaper than rechargeable ones. But since you can just recharge and re-use rechargeable batteries, they last longer nad work out cheaper in the long run.
How are lithium batteries rechargeable?
Lithium cells are used in mobile phones and laptops. One type of lithium cell is made up of a lithium cobalt oxide electrode and a graphite electrode. The electrolyte is a lithium salt in an organic solvent.
How do you recharge lithium batteries?
To recharge those batteries, a current is supplied to force electrons to flow in the opposite direction around the circuit and reverse the reaction. The reactions that take place in non-rechargeable batteries are difficult or impossible to reverse in this way.
How can fuel cells generate energy from hydrogen and oxygen?
In most cells, the chemicals that generate the electricity are contained in the electrodes and the electrolytes that form the cell. In a fuel cell, the chemicals are stored separately outside the cell and fed when electricity is required. One example of this is the alkaline hydrogen-oxygen fuel cell, which can be used to power electric vehicles. Hydrogen and oxygen gases are fed into two separate platinum-containing electrodes. The electrodes are separated by an anion-exchange membrane that allows anions and water to pass through it, but not hydrogen and oxygen gas. The electrolyte is an aqueous alkaline solution.
What are the advantages of fuel cells?
- they are more efficient
- less energy is wasted as heat
- water is the only waste product
- they don’t need to be recharged, only H and O need to be supplied
What is the downside of fuel cells?
- you need energy to produce a supply of H and O
- electricity for the electrophoresis of water is produced by burning fossil fuels
- hydrogen is flammable so it needs to be handled carefully when it is stored or transported.
