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Questions and Answers
What type of electrodes are used in the Downs cell?
What type of electrodes are used in the Downs cell?
What material is the anode made of in the Downs cell?
What material is the anode made of in the Downs cell?
What prevents iron, the cathode material in the Downs cell, from being oxidized?
What prevents iron, the cathode material in the Downs cell, from being oxidized?
What occurs at the anode in the Downs cell?
What occurs at the anode in the Downs cell?
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Why is calcium chloride added to molten sodium chloride in the Downs cell process?
Why is calcium chloride added to molten sodium chloride in the Downs cell process?
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Which metal is mentioned as being difficult to reduce from Na+ ions to the metal form?
Which metal is mentioned as being difficult to reduce from Na+ ions to the metal form?
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What was Humphry Davy's contribution to the isolation of sodium?
What was Humphry Davy's contribution to the isolation of sodium?
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Why is a mixture of sodium chloride/calcium chloride used as the electrolyte in the Downs cell?
Why is a mixture of sodium chloride/calcium chloride used as the electrolyte in the Downs cell?
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Why should there be no contact between Cl2 and Na in the Downs cell?
Why should there be no contact between Cl2 and Na in the Downs cell?
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Why is it more cost-effective to use aqueous electrolytes over molten electrolytes?
Why is it more cost-effective to use aqueous electrolytes over molten electrolytes?
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What role does an iron mesh screen play in the Downs cell?
What role does an iron mesh screen play in the Downs cell?
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In general, what is one of the main disadvantages of using a molten electrolyte in electrolysis?
In general, what is one of the main disadvantages of using a molten electrolyte in electrolysis?
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Study Notes
The Downs Cell
- The Downs cell is used to produce sodium and chlorine in commercial quantities.
- The cell uses inert (unreactive) electrodes: a graphite anode and an iron cathode.
- At the cathode, Na+ ions are reduced to sodium metal: Na+(l) + e- → Na(l)
- At the anode, 2Cl- ions are oxidized to chlorine gas: 2Cl-(l) → Cl2(g) + 2e-
- The overall cell reaction is: 2Na+(l) + 2Cl- → 2Na(l) + Cl2(g)
Molten Electrolytes
- In the electrolysis of a molten electrolyte, anions are oxidized at the anode and cations are reduced at the cathode.
- Water is not present to interfere with the desired reactions.
- Calcium chloride is added to molten sodium chloride to lower its melting point, but it does not affect the overall cell reaction.
History of Sodium Isolation
- Sodium was first isolated by electrolysis in 1807 by Humphry Davy.
- Davy electrolysed molten sodium hydroxide to isolate sodium.
- He was the first person to isolate sodium, potassium, calcium, barium, magnesium, boron, and strontium using electrolysis.
Advantages and Disadvantages of Molten Electrolytes
- The advantage of using a molten electrolyte is that there is no water present to interfere with the desired reactions.
- The main disadvantage is that the process requires much more energy to maintain the electrolyte in a molten state.
Operating the Downs Cell
- The electrolyte is a mixture of sodium chloride and calcium chloride in a 1:2 ratio, which lowers the melting point of sodium chloride from 801 °C to about 600°C.
- An iron mesh screen is used to keep the products at the anode and cathode apart.
- The construction and operation of the Downs cell minimizes contact between the two products to prevent them from reacting to re-form sodium chloride.
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Description
Explore the use of molten electrolytes in commercial electrolytic cells, specifically focusing on the Downs cell that produces sodium and chlorine. Learn about the inert electrodes used in the cell, such as graphite for the anode and iron for the cathode.
