electrolysis
TRANSCRIPT
ElectrolysisElectrolysis
the passage of a direct electric current through an ionic substance that is either molten or dissolved in a suitable solvent, resulting in chemical reactions at electrodes and separation of materials.
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Requirements of Requirements of electrolysiselectrolysis
An electrolyte - It is a substance containing free ions which are the carriers of electric current in the electrolyte
A direct current (DC) supply - It provides the electrical energy necessary to create or discharge the ions in the electrolyte. Electrical current is carried by electrons in the external circuit.
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Requirements of Requirements of electrolysiselectrolysis
Two electrodes - Electrode is an electrical conductor which provides the physical interface between the electrical circuit providing the energy and the electrolyte.
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Requirements of Requirements of electrolysiselectrolysis
The following figure shows the electrolyte, battery
( power supply) and electrodes
( cathode and anode ) required for electrolysis.
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ElectrolysisElectrolysis
Molecule of solid copper chloride
CuCl2 (s)
Molecule of solid copper chloride after being dissolved
CuCl2 (aq)chloride
ionCopper
ion
If you melt or dissolve an ionic compound (such If you melt or dissolve an ionic compound (such as NaCl or CuClas NaCl or CuCl22), then the ions become free to ), then the ions become free to move around – and carry electrical current.move around – and carry electrical current.
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ElectrolysisElectrolysis
Electrolysis is Electrolysis is used to used to separate a separate a metal from metal from its its compound.compound.
= chloride ion
= copper ion
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Purifying CopperPurifying Copper
++++
----
Solution containing copper ions
Impure copper
Cu2+
Cu2+
Cu2+
Pure copper
At the anode:
Cu(s) Cu2+(aq) + 2e-
At the cathode:
Cu2+(aq) + 2e- Cu(s)
13/04/23Electrolysis equationsElectrolysis equationsWe need to be able to write “half equations” to show what happens during electrolysis (e.g. for copper chloride):
2 2
2
At the negative electrode the positive ions GAIN electrons to
become neutral copper ATOMS. The half equation is:
Cu2+ + e- Cu
At the positive electrode the negative ions LOSE electrons to
become neutral chlorine MOLECULES. The half equation is:
Cl- - e- Cl2
Oxidation and Reduction in Oxidation and Reduction in ElectrolysisElectrolysis
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At the negative electrode the
positive ions GAIN electrons – this is called Reduction. The half equation
is:
Cu2+ + 2e- Cu
At the positive electrode the
negative ions LOSE electrons –This is called Oxidation.
The half equation is:
2Cl- - 2e- Cl2
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Electrolysis of brineElectrolysis of brine
Positive electrode
Negative electrode
Sodium chloride (brine)
NaCl(aq)
Sodium hydroxide (NaOH(aq)). Used to make soap, paper
and ceramics
Sodium chloride (salt) is made of an alkali metal and a halogen. When it’s dissolved we call the solution “brine”, and we can electrolyse it to produce 3 things…
Chlorine gas (Cl2) – used to kill bacteria and to make acids, bleach and plastics
Hydrogen gas (H2) – used to manufacture ammonia and margarine