Chlorine Flashcards
how is chlorine manufactured?
Chlorine is manufactured by the electrolysis of seawater using a diaphragm cell.
what are the products of the electrolysis of brine?
chlorine gas (Cl₂), hydrogen gas (H₂), and sodium hydroxide (NaOH)
electrolyte
concentrated aq. sodium chloride solution(brine)
Anode
Titanium electrodes (inert conductors)
Cathode
Steel grids
Voltage source
Provides electrical energy to drive the reaction
Process of electrolysis of brine
Seawater is pumped into the anode compartment. Chloride ions are discharged at the titanium anode to produce Cl2 (g).
2Cl- - 2e- → Cl2 (g)
H+ ions are discharged at the steel cathode to produce H2 (g).
2H+ (aq) + 2e → H2 (g)
A porous asbestos diaphragm separated the cell into an anode and cathode compartment.
The liquid flowing from the base of the tank is a mixture of NaOH and NaCl solutions. This mixture is evaporated to ⅕ of its volume. NaCl crystallises and the remaining liquid is NaOH solution.
Oxidationnat the anode
Both chloride and hydroxide ions move to the anode.
Chloride ions are oxidized to chlorine gas because they are in a greater concentration than the hydroxide ions.
Reduction at the cathode
Both sodium and hydrogen ions move to the cathode.
Hydrogen ions from water are reduced to hydrogen gas.
Sodium is more reactive than hydrogen, so hydrogen from water is discharged instead.
Hydrogen gas is pumped off from the top of the cathode compartment
How is NaOH manufactured?
Asbestos diaphragm keeps the hydrogen and chlorine separated as they will not react.
The level of brine is kept higher in the anode compartment than in the cathode compartment. This is done to have a flow towards the cathode compartment.
This prevents the chlorine from reacting with the NaOH.
Equation to show the electrolysis reaction
Cl2 (g) + 2NaOH (aq) → NaClO (aq) + NaCl (aq) + H2O (l)
Advantages of the diaphragm cell
Produces no toxic mercury
Works with brine of fairly low purity
Cheap to construct
Uses of NaOH
To make soap detergents, paper
Oil refining
Purification of bauxite
Uses of chlorine
Treatment of water
Manufacture of CFCs and PVC
Manufacture of bleach
Manufacture of solvents used in dry cleaning
Manufacture of antiseptics and insecticides
Mercury waste on the environment
Toxic and can kill fish and poison people who eat it
Asbestos on the environment
When it dries out, asbestos fibres are released in the air to cause lung conditions and increases risk of lung cancer
NaOH leaks
Can alter the pH of water and cause death of organisms
Depletion of ozone layer
Many chlorofluorocarbons, tetrachloromethane and trichloromethane in solvents destroy ozone
Polyvinyl chloride
This is used in construction, packaging and other industries
It is not biodegradable so wastes contribute to litter and landfill
Some of it is burnt in controlled waste recycling and as a source of energy → puts poisonous dioxins and acidic HCl in the atmosphere
