Mercury Cell Flashcards
What single improbable truth does the mercury cell rely on?
When the cathode is mercury, the lower energy option for a cathode reaction ceases to be reduction of hydrogen and becomes instead:
Na + e- —> Na(Hg)
In the diaphragm cell some hydroxide ions diffuse into the ____ compartment and sodium hydroxide reacts with chlorine. The mercury cell provides the ultimate way
of keeping the ____ away from the sodium hydroxide, since no sodium hydroxide has been made yet.
anode
chlorine
What is pumped into the first compartment?
Concentrated brine is pumped into the first compartment where the Cl- ions are oxidised to form Cl2 at the anode.
What happens at the cathode?
The cathode is made from liquid mercury which attracts the Na+ ions, which are preferentially reduced to form a sodium-mercury amalgam, Na(Hg).
What happens to the amalgam in the second compartment? (2)
This amalgam is then transported into a second compartment where it is reacted with water
o The Na will react as predicted with water according to the equation Na + H2O —> NaOH + H2
o The Hg will not react with water and can be recycled back into the first compartment.
True or false
The products remain NaOH, Cl2 and H2, albeit produced slightly differently.
True
The chlorine gas produced is very ___.
pure
What are the limitations of the mercury cell? (2)
o Mercury is a very toxic substance and is difficult to work with safely.
o This cell operates with higher energy requirements than the others and as such is seldom used industrially anymore.
The type of electrode can influence the E value. Why?
As redox occurs on the surface of the electrode. Different materials interact differently with chemicals.
Decomposer reaction:
2Na (Hg) + 2H2O –> 2NaOH + H2
How is the NaOH and H2 formed?
Na + H2O —> NaOH + H2
