C6 - Electrolysis Flashcards
define electrolysis
use of an electrical current to break down compounds containing ions
what is the substance being broken down called?
electrolyte
what are the electrodes made from?
substances that conduct electricity.
during electrolysis, what moves to the anode (positive electrode)?
negatively charged ions
during electrolysis, what moves to the cathode (negative electrode)
positvely charged ions
for the electrolysis of molten ionic compounds, what must the electrodes be and why?
the electrodes must be inert so that they do not react with the electrolyte or the products.
when can ionic substances ONLY conduct electricity?
when they are molten or dissolved in water
when does reduction occur?
when positively charged ions gain electrons at the negative electrode
when does oxidation occur?
when negatively charged ions lose electrons at the positive electrode
what happens in a redox reaction?
both reduction and oxidation occur.
To extract metals from their ores using electrolysis, what must they be?
more reactive than carbon
why is electrolysis an expensive process?
as it requires a lot of heat and electrical energy
how is aluminium obtained?
by the electrolysis of aluminium oxide that has been mixed with cryolite
what does cryolite do?
lowers the melting point of aluminium oxide. less energy needed
where does aluminium form?
negative electrode
where does oxygen gas form?
at the positive carbon electrode and reacts with the carbon forming carbon dioxide
what is the positive electrode made of when electrolysis is used to extract a metal?
carbon
what do the water molecules break down to form when ionic compounds are dissolved in water to form aqueous solutions?
hydroxide ions (OH-) , hydrogen ions (H+)
what is produced at the negative electrode?
hydrogen if the metal is more reactive than hydrogen. metal is produced if metal is less reactive than hydrogen
what is produced at the positive electrode?
oxygen is produced unless solution contains halide ions. if halide ions are present, halogen is produced
what happens in the electrolysis of sodium chloride solution?
hydrogen is released at negative electrode, chlorine gas released at positive electrode.
Investigate what happens when aqueous solutions are electrolysed using inert electrodes. REQUIRED PRACTICAL
Sample method: set up equipment, pass an electric current through aqueous solution. observe products formed at each inert electrode.
explain how copper is produced from copper sulfate solution by electrolysis
- copper ions are positive so they are attracted to the inert cathode
- copper ions gain electrons at the intert cathode so they are reduced to form copper atoms
Suggest why the colour of the copper(II) sulfate solution fades during the electrolysis.
- copper ions cause the blue colour.
- copper ions are reduced to copper ions so the concentration of copper ions decreased
what products do you get when brine is electrolysed?
chlorine gas at anode
hydrogen gas at cathode
sodium hydroxide solution
