Topic 9 – Electrolytic cells
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Electrolytic cells
1.
2.
(i)
Draw a diagram of apparatus that could be used to electrolyse molten
sodium chloride (NaCl).
(ii)
Solid sodium chloride does not conduct electricity but molten sodium
chloride does. Explain this difference, and outline what happens in an
electrolytic cell during the electrolysis of molten sodium chloride using
carbon electrodes.
(iii)
State the products formed and give equations showing the reactions at
each electrode.
(iv)
State what practical use is made of this process.
(i)
Draw a diagram of apparatus that could be used to electrolyse molten
potassium bromide. Label the diagram to show the polarity of each
electrode and the product formed.
(ii)
Describe the two different ways in which electricity is conducted in the
apparatus.
(iii) Write an equation to show the formation of the product at each electrode.
Determine the mole ratio in which the substances are formed.
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Topic 9 – Electrolytic cells
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Answers:
1.
(i)
(ii)
Sodium chloride crystals consist of ions in a rigid lattice that cannot
move about - when melted the ions are free to move.
The positive sodium ions are attracted to the negative electrode (cathode)
and the negative chloride ions are attracted to the positive electrode
(anode)
(iii)
At the anode: chlorine gas is formed 2Cl-(l)  Cl2(g) + 2eAt the cathode: sodium metal is formed Na+(l) + e-  Na(l)
(iv)
manufacture of sodium and chlorine (not mentioned in the video but
worth knowing).
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Topic 9 – Electrolytic cells
2.
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(i)
(ii)
Electrons flow through connecting wires
Ions move through the electrolyte to the electrodes and are oxidized or
reduced.
(iii)
Anode: 2Br-(l)  Br2(l) + 2eCathode: K+(l) + e-  K(l)
mol ratio K : Br2 2:1
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