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Electrolysis
the passage of a direct electric current
through an ionic substance that is
either molten or dissolved in a ...
Requirements of electrolysis

08/03/14

An electrolyte - It is a substance containing
free ions which are the carriers of...
Requirements of electrolysis

08/03/14

Two electrodes - Electrode is an electrical
conductor which provides the physical...
Requirements of electrolysis

08/03/14

The following figure
shows the
electrolyte, battery
( power supply) and
electrodes...
Electrolysis

If you melt or dissolve an ionic compound (such as
NaCl or CuCl2), then the ions become free to move
around ...
Electrolysis
Electrolysis is
used to
separate a
metal from its
compound.
= chloride ion

= copper ion

08/03/14
Purifying Copper

Impure
copper
Solution
containing
copper ions

+
+ Cu
+ Cu
+ Cu

At the anode:
Cu(s)

Cu2+(aq) + 2e-

2+...
Electrolysis equations

08/03/14

We need to be able to write “half equations” to show what
happens during electrolysis (e...
08/03/14

Oxidation and Reduction in Electrolysis
At the positive
electrode the
negative ions LOSE
electrons –This is
call...
Electrolysis of brine

08/03/14

Sodium chloride (salt) is made of an alkali metal and a
halogen. When it’s dissolved we c...
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Electrolysis

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Electrolysis

  1. 1. Electrolysis 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. 08/03/14
  2. 2. Requirements of electrolysis 08/03/14 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.
  3. 3. Requirements of electrolysis 08/03/14 Two electrodes - Electrode is an electrical conductor which provides the physical interface between the electrical circuit providing the energy and the electrolyte.
  4. 4. Requirements of electrolysis 08/03/14 The following figure shows the electrolyte, battery ( power supply) and electrodes ( cathode and anode ) required for electrolysis.
  5. 5. Electrolysis If you melt or dissolve an ionic compound (such as NaCl or CuCl2), then the ions become free to move around – and carry electrical current. Molecule of solid copper chloride CuCl2 (s) Molecule of solid copper chloride after being dissolved chloride ion Copper ion CuCl2 (aq) 08/03/14
  6. 6. Electrolysis Electrolysis is used to separate a metal from its compound. = chloride ion = copper ion 08/03/14
  7. 7. Purifying Copper Impure copper Solution containing copper ions + + Cu + Cu + Cu At the anode: Cu(s) Cu2+(aq) + 2e- 2+ --- 08/03/14 Pure copper 2+ 2+ At the cathode: Cu2+(aq) + 2e- Cu(s)
  8. 8. Electrolysis equations 08/03/14 We need to be able to write “half equations” to show what happens during electrolysis (e.g. for copper chloride): At the negative electrode the positive ions GAIN electrons to become neutral copper ATOMS. The half equation is: Cu2+ + 2e- Cu At the positive electrode the negative ions LOSE electrons to become neutral chlorine MOLECULES. The half equation is: 2 Cl- - 2e- Cl2
  9. 9. 08/03/14 Oxidation and Reduction in Electrolysis At the positive electrode the negative ions LOSE electrons –This is called Oxidation. The half equation is: At the negative electrode the positive ions GAIN electrons – this is called Reduction. The half equation is: 2Cl- - 2e- Cu2+ + 2e- Cl2 Cu
  10. 10. Electrolysis of brine 08/03/14 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 Sodium chloride (brine) NaCl(aq) Positive electrode Negative electrode Sodium hydroxide (NaOH(aq)). Used to make soap, paper and ceramics

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