Topic 4 Chemical Changes Flashcards
Key Terms/Key Knowledge
What is electrolysis?
The splitting up of an ionic compound using electricity. The electric current is passed through a substance causing chemical reactions at the electrodes and the decomposition of the materials.
What is an electrolyte?
A solution containing free ions from the molten or dissolved ionic substance. The ions are free to move to carry charge.
What is the positive electrode?
Anode
What is the negative electrode?
Cathode
What happens at the cathode? (Higher Only)
It is where positively charged ions gain electrons and so the reactions are reductions.
What happens at the anode? (Higher Only)
It is where negatively charged ions
lose electrons and so the reactions are oxidations.
In aqueous solutions what is produced at the negative electrode (cathode)?
Hydrogen is produced if the metal in the electrolyte is more reactive than hydrogen.
A solid coat layer of the pure metal will form on the cathode if less reactive than hydrogen.
In aqueous solutions what is produced at the positive electrode (anode)?
Oxygen is produced from the discharged hydroxide ions unless the solution contains halide ions then the halogen is produced.
What happens to the ions during electrolysis?
Positively charged ions move to the negative electrode (cathode), and negatively charged ions move to the positive electrode (anode).
Where are metals formed? Why?
Cathode because metals are positive ions.
Where are non-metals formed? Why?
Anode because non-metals are negative ions.
What is OILRIG?
Oxidation Is Loss (of electrons)
Reduction Is Gain (of electrons)
In electrolysis of lead bromide (molten ionic compound) what is produced where?
The metal (lead) is produced at the cathode and the non-metal (bromine) is produced at the anode.
Why is extracting metals from electrolysis expensive?
Because large amounts of energy are used in the extraction process to melt the compounds and to produce the electrical current.
Why can solid substances not be electrolysed?
They do not conduct electricty, or the ions cannot move.
Why is aluminium oxide mixed with cryolite?
Because aluminium oxide has a very high melting point and cryolite can lower it so it is easier to melt.
What metals are extracted by electrolysis?
Metals more reactive than carbon.
Metals that have reacted with carbon also.
In electrolysis of aluminium oxide why do the anodes have to be replaced?
Because oxygen is formed, which reacts with the carbon of the positive electrodes, forming carbon dioxide, and they gradually burn away .
What are the anodes in electrolysis of aluminium oxide made of ?
Graphite
What is an acid?
Acids produce hydrogen ions (H+) in aqueous solutions. They have a pH range of 0-6.
What is an alkali?
Alkalis produce hydroxide ions (OH-) in aqueous solutions. They have a pH range of
8-14.
What is Displacement ?
A chemical reaction in which a more reactive element displaces a less reactive element from its compound.
What is Extraction?
Extraction techniques are used to separate a desired substance when it is mixed with others.
What is Neutralisation?
Neutralisation
