electrolytical cells Flashcards
Define Electrolytic cells
electrode reactions that are sustained by a supply of electrical energy
conversion of electrical energy into chemical energy
What occurs at at the anode of mercury cell
Brine (concentrated sodium chloride is pumped into the compartment with the anode, where chlorine ions undergo oxidation to for chlorine gas
What occurs at the cathode of a mercury cell
sodium ions undergo reduction to form molten sodium at at the mercury cathode
What does sodium form
at the cathode sodium forms an amalgam with mercury
amalgam is then moved to a separate compartment containing water where redox reaction occurs between water and sodium. This forms hygrogen gas and hydorxyl ions which for sodium hydorxide
Why isnt the mercury no longer used
mercury is toxic and high electricity usage.
describe how diaphragm cell works in aonde
1- concentarated sodium chloride is pumped into the compartment with the anode, where chlorine ions ungergo oxidation to form chlorine gas
what seperates the anode and cathode
asbestos diaphragm, it does not control the flow of ions
why is the volume of anode and cathode at different volumes
the volume of sodium chloride solution in the anode must be greater than the volume in cathode because this creates a pressure gradient which ensures that ions only flow in one direction. also stops sodium hydroxide formed at the the cathode from moving into anode compartment
Why is diaphragm cell no longer used
toxicity of asbestos
least effective concentration of sodium hydroxide lower
describe how to membrane cell occurs
concentrated sodium chloride pumped anode where chloride ions undergo oxidation
brine is continusoly pumped into the cathode to ensure high concentration of chloride ions
pure water is continusoly pumped into the cathode compartment as sodium hydroxide is extracted
What is the membrane
anode and cathode are separated by an ion exchange membrane. only allows sodium ions to pass through
what is an advantage of the membrane
most cost effective
environmentally friendly
concentration of the sodium hydroxide can be controlled during the process
Describe extraction of aluminum
Aluminuim is dissolved in molten cryolite which lowers the melthing pint
the molten aluminium is then placed in a reaction vessel where electrolysis takes place to extract alumnium
Why so carbon electrodes need to be replaced
due to the high temperature in the reaction, the oxygen gas reacts with carbon anode to produce carbon dioxide gas
Why is the downside of extraction of aluminum
high energy usage which makes the process expensive
Cyolite is expensive to manufacture and toxic- bad for the environment
