What is brine?
sodium chloride solution (NaCl)
Where is sodium chloride found in nature?
in oceans and seas
found in large deposits in the ground - the salt can be extracted from underground deposits by solution mining
How does solution mining work?
very hot water under pressure is pumped down into the salt deposits
the salt dissolves and the solution is pumped back to the surface
What are the four ions in brine (aqueous sodium chloride)?
Explain the chlor-alkali diaphragm cell
the electrolysis of brine is carried out in a diaphragm cell
the cell is designed to keep the products apart
the porous diaphragm only lets sodium ions go through, not hydroxide ions nor the chloride ions
the cathode is made of steel
the anode is made of titanium because steel would react with the chlorine produced; titanium is less reactive than steel
there is a higher level of brine on the anode side - this makes sure that the flow of liquid is always from the anode to the cathode which prevents spdium hydroxide solution formed finding its way back to where chlorine is being produced
Explain why diaphragm cell is designed to keep the products apart?
if chlorine comes into contact with sodium hydorxide solution, it reacts to make bleach - a micture of sodium chloride and sodium chlorate (I) solution (NaClO)
if chlorine comes into contact with hydrogen, it produces a mixture which would explode violently on exposure to sunlight or heat to give hydrogen chloride
What are the products of the electrolysis of brine?
Sodium Hydroxide (NaOH)
What is produced at the titanium anode? What is the half equation for this?
2Cl- (aq) → Cl2 (g) + 2e-
What is produced at the steel cathode? What is the half equation for this?
hydrogen gas (it is too difficult to discharge sodium ions so hydrogen ions from the water are discharged instead)
2H+ (aq) + 2e- → H2 (g)
What is left in solution?
the sodium ions (Na+) and the hydroxide ions (OH-) from the water are left in solution
sodium hydroxide solution is formed
How is the sodium hydroxide solution left in solution concentrated? Why is is concentrated?
It is concentrated because is it contaminated with unchanged sodium chloride
It is concentrated by evaporating it. During this process, most of the sodium chloride crystallises out as as solid salt. This can be separated, redissolved in water and recycled back through the cell again
What is the full equation of the electrolysis of brine?
2H+ (aq) + 2Cl- → Cl2 (g) + H2 (g)
What are three uses of chlorine?
sterilising water (chlorination) to make it safe to drink
making hydrochloric acid (by controlled reaction with hydrogen)
What are uses of sodium hydroxide?
the purification of bauxite to make aluminium oxide (alumina) as a part of the manufacture of aluminium
making paper - the sodium hydroxide helps break the wood down into pulp
making soap - sodium hydroxide reacts with animal and vegetabl fats and oils to make compounds, such as sodium stearate, that are present in soap
making bleach - bleach is formed when sodium hydroxide and chlorine react together in the cold; it is a mixture of sodium chlordie and sodium chlorate (I) solution (NaClO)
Sodium hydroxide is a very strong ... and is used widely in the ...
Sodium hydroxide is a very strong base and is used widely in the chemical industry