Electrolysis Flashcards
What does electrolysis mean?
Splitting up with electricity
What is the process of electrolysis?
If you pass an electric current through an ionic substance that is molten or in a solution, it breaks down into the elements it is made of.
What is the electrolyte?
A liquid that is required during electrolysis that conducts electricity.
What do the electrolytes contain?
Free ions that conduct electricity and allow the whole thing to work.
What are the electrolytes usually?
Molten or dissolved in a solution.
What is required for an electrical circuit to work?
There has to be a flow of electron. Electrons are taken away from ions at the positive electrode and given to other ions at the negative electrode.
What happens as ions lose or gain electrons?
They become atoms or molecules and are released.
What is oxidation?
The loss of electrons?
What is reduction?
The gain of electrons.
What is a redox reaction?
An oxidation-reduction (both of them) reaction.
What is the anode?
The positive electrode.
What is the cathode?
The negative electrode.
What are positive ions called?
Cations 🐈
What are negative ions called?
Anions
Where do the cations go?
To the cathode.
Where do the anions go?
To the anode.
Where does reduction happen?
At the cathode.
Where does oxidation happen?
At the anode.
Properties of a molten solid?
Only the ions of the solid are present.
Properties of an ionic solution?
A mix of ions of the solid and ions of water are present.
Relies on the ionic compound being solid in water.
What are the advantages of a molten solid?
Can only get pure products.
What are the disadvantages of a molten solid?
It requires heating which is expensive, difficult and hazardous.
What are the advantages of an ionic solution?
Safe and easy to do in a lab.
What are the disadvantages of an ionic solution?
It is a mix of ions from water which means you get a greater mix of products.
If an ionic compound isn’t solid you can’t do this.
Why does electrolysis not work with solid ionic compounds?
The ions are held together in a lattice structure, they are fixed in position, meaning that the separate elements cannot go to the anode or the cathode.
What is vital to perform electrolysis?
In a solid ionic compound you would need to turn it into a molten compound. You would melt the compound by heating it or you would dissolve it in a solution.
What is the electrolysis of aluminium used for?
To remove aluminium from its ore.
What is aluminium’s main ore?
Bauxite.
Describe aluminium.
A very abundant metal but is found naturally in compounds.
What is aluminium left as after mining and purifying?
A white powder: pure Al2o3- aluminium oxide.
What is cryolite used for in the electrolysis of aluminium?
Aluminium oxide has a very high melting point of over 2000 degrees, so melting would be very expensive. Cryolite lowers the melting point and therefore, the cost.
How is cryolite made a part of aluminium oxide?
The aluminium oxide is dissolved in the molten cryolite- which is a less common ore of aluminium.
What does the molten cryolite bring the melting point of Al2o3 to?
Around 900 degrees.
What are he electrodes in the electrolysis of aluminium oxide made from?
Carbon.
In the electrolysis of aluminium oxide, what forms at the negative electrode (cathode)?
Aluminium
In the electrolysis of aluminium oxide, what forms at the positive electrode (anode)?
Oxygen
Why does the positive electrode gradually get ‘eaten away’ and have to be replaced every now and again?
Because the carbon reacts with the oxygen to form carbon dioxide.
What are the products of the electrolysis of brine and what are their uses?
Hydrogen- rocket fuel.
Chlorine- swimming pool disinfectant, making plastics.
Sodium hydroxide- bleach, removing pollutants from water, soaps and detergents.
When a salt is molten what will it conduct?
Electricity
In the electrolysis of lead bromide, what happens to the positive ions?
They are attracted to the negative electrode. Here they undergo reduction and lead is produced at the cathode.
In the electrolysis of lead bromide, what happens to the negative ions?
They are attracted to the positive electrode. Here they undergo oxidation and bromine is produced at the anode.
What does one lead ion accept at the cathode?
Two electrons in order to become one lead atom.
At the anode, what do two bromide ions lose?
One electron each and they become one bromine ion.
How does reactivity affect the products formed by electrolysis at the cathode?
If a salt is dissolved in water there will also be some H+ and OH- ions.
At the cathode, if metal ions and H+ ions are present, the metal ions will stay in the solution if the metal is more reactive than hydrogen because the more reactive the element the keener it is to stay as an ion.
Hydrogen will be produced unless the metal is less reactive than it.
How does reactivity affect the products formed by electrolysis at the anode?
If OH- and halide ions (Cl-, Br-, I-) are present, then molecules of chlorine, bromine and iodine will be produced. If no halide ions are present oxygen will form
What are the useful products of the electrolysis of sodium chloride?
Hydrogen, chlorine, sodium hydroxide.
What happens at the negative electrode in the electrolysis of sodium chloride?
Two hydrogen ions accept two electrons to become one hydrogen molecule.
What happens at the positive electrode during the electrolysis of sodium chloride?
Two chloride ions lose their electrons and become one chlorine molecule.
What happens to the sodium ions in the electrolysis of sodium chloride?
They stay in the solution because they are more reactive that hydrogen. Hydroxide ions are also left behind , meaning that sodium hydroxide (NAOH) is left in the solution.
What does Metal + water =?
Metal hydroxide + hydrogen
Acid + metal =?
Salt + hydrogen
