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ELECTROLYSIS A guide for GCSE students

ELECTROLYSIS A guide for GCSE students. 2010 SPECIFICATIONS. KNOCKHARDY PUBLISHING. ELECTROLYSIS. INTRODUCTION

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ELECTROLYSIS A guide for GCSE students

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  1. ELECTROLYSIS A guide for GCSE students 2010 SPECIFICATIONS KNOCKHARDY PUBLISHING

  2. ELECTROLYSIS INTRODUCTION This Powerpoint show is one of several produced to help students understand selected GCSE Chemistry topics. It is based on the requirements of the AQA specification but is suitable for other examination boards. Individual students may use the material at home for revision purposes and it can also prove useful for classroom teaching with an interactive white board. Accompanying notes on this, and the full range of AS and A2 Chemistry topics, are available from the KNOCKHARDY WEBSITE at... www.knockhardy.org.uk All diagrams, photographs and any animations in this Powerpoint are original and created by Jonathan Hopton. Permission must be obtained for their use in any work that is distributed for financial gain.

  3. ELECTROLYSIS • CONTENTS • What is electrolysis? • Electrolysis of ionic compounds • Electrolysis of molten sodium chloride • Electrolysis of aqueous sodium chloride (brine) • Diaphragm cell • Electrolysis of aluminium oxide • Other electrolytic systems • Electrolysis of water

  4. ELECTROLYSIS Passing an electric current through ionic substances that are molten or in aqueous solution, breaks them down into elements.

  5. ELECTROLYSIS Passing an electric current through ionic substances that are molten or in aqueous solution, breaks them down into elements. The process is known asELECTROLYSIS

  6. ELECTROLYSIS Passing an electric current through ionic substances that are molten or in aqueous solution, breaks them down into elements. The process is known as ELECTROLYSIS The substance broken down is called theELECTROLYTE

  7. ELECTROLYSIS Passing an electric current through ionic substances that are molten or in aqueous solution, breaks them down into elements. The process is known as ELECTROLYSIS The substance broken down is called the ELECTROLYTE During electrolysis… Positively charged ions move to the negative electrode - CATHODE Negatively charged ions move to the positive electrode - ANODE

  8. ELECTROLYSIS Passing an electric current through ionic substances that are molten or in aqueous solution, breaks them down into elements. The process is known as ELECTROLYSIS The substance broken down is called the ELECTROLYTE During electrolysis… Positively charged ions move to the negative electrode - CATHODE Negatively charged ions move to the positive electrode - ANODE CATHODE +ive ions gain electronsREDUCTION ANODE - ive ions give up (lose) electrons OXIDATION

  9. ELECTROLYSIS OF IONIC COMPOUNDS

  10. CONDUCTING ELECTRICITY

  11. CONDUCTING ELECTRICITY For a substance to conduct electricity it must have either…

  12. CONDUCTING ELECTRICITY For a substance to conduct electricity it must have either… electrons which are free to move about (metals / graphite)

  13. CONDUCTING ELECTRICITY For a substance to conduct electricity it must have either… electrons which are free to move about(metals / graphite) or ionswhich are free to move about

  14. CONDUCTING ELECTRICITY For a substance to conduct electricity it must have either… electrons which are free to move about (metals / graphite) or ionswhich are free to move about When an ionic substance is melted or dissolved in water, the ions are free to move about within the liquid or solution.

  15. Na+ Na+ Na+ Na+ Na+ Na+ Cl- Cl- Cl- Cl- Cl- Cl- ELECTROLYSIS OF IONIC COMPOUNDS SOLID WHEN SOLID, THE IONS ARE NOT FREE TO MOVE NO CONDUCTION OF ELECTRICITY SOLID IONIC COMPOUNDS DON’TCONDUCT ELECTRICITY

  16. Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Cl- Cl- Cl- Cl- Cl- Cl- Cl- Cl- Cl- Cl- ELECTROLYSIS OF IONIC COMPOUNDS SOLID MOLTEN WHEN SOLID, THE IONS ARE NOT FREE TO MOVE NO CONDUCTION OF ELECTRICITY WHEN MOLTEN, THE IONS ARE FREE TO MOVE ELECTRICITY IS CONDUCTED MOLTEN IONIC COMPOUNDS DOCONDUCT ELECTRICITY

  17. Na+ Na+ Na+ Na+ Na+ Na+ Cl- Cl- Cl- Cl- Cl- Cl- ELECTROLYSIS OF IONIC COMPOUNDS SOLID WHEN SOLID, THE IONS ARE NOT FREE TO MOVE NO CONDUCTION OF ELECTRICITY SOLID IONIC COMPOUNDS DON’TCONDUCT ELECTRICITY

  18. Na+ Na+ Na+ Na+ Na+ Na+ Cl- Cl- Cl- Cl- Cl- Cl- ELECTROLYSIS OF IONIC COMPOUNDS SOLID Add to water WHEN SOLID, THE IONS ARE NOT FREE TO MOVE NO CONDUCTION OF ELECTRICITY AQUEOUS SOLUTIONS OF IONIC COMPOUNDS DOCONDUCT ELECTRICITY

  19. Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Cl- Cl- Cl- Cl- Cl- Cl- Cl- Cl- Cl- Cl- ELECTROLYSIS OF IONIC COMPOUNDS SOLID IN AQUEOUS SOLUTION WHEN SOLID, THE IONS ARE NOT FREE TO MOVE NO CONDUCTION OF ELECTRICITY WHEN DISSOLVED IN WATER, THE IONS ARE FREE TO MOVE ELECTRICITY IS CONDUCTED AQUEOUS SOLUTIONS OF IONIC COMPOUNDS DOCONDUCT ELECTRICITY

  20. ELECTROLYSIS OF MOLTEN SODIUM CHLORIDE

  21. ELECTROLYSIS OF SODIUM CHLORIDE DOWNS CELL

  22. ELECTROLYSIS OF SODIUM CHLORIDE SOLID SODIUM CHLORIDE DOESNOTCONDUCT ELECTRICITY BECAUSE THE IONS ARE NOT FREE TO MOVE TO THE ELECTRODES

  23. ELECTROLYSIS OF SODIUM CHLORIDE SOLID SODIUM CHLORIDE DOES NOT CONDUCT ELECTRICITY BECAUSE THE IONS ARE NOT FREE TO MOVE TO THE ELECTRODES WHEN MOLTEN, THE IONS HAVE MORE FREEDOM AND CAN MOVE

  24. ELECTROLYSIS OF SODIUM CHLORIDE SOLID SODIUM CHLORIDE DOES NOT CONDUCT ELECTRICITY BECAUSE THE IONS ARE NOT FREE TO MOVE TO THE ELECTRODES WHEN MOLTEN, THE IONS HAVE MORE FREEDOM AND CAN MOVE SODIUM IONS GO TO THE CATHODE AND EACH PICK UP AN ELECTRON Na+ + e- Na

  25. ELECTROLYSIS OF SODIUM CHLORIDE SOLID SODIUM CHLORIDE DOES NOT CONDUCT ELECTRICITY BECAUSE THE IONS ARE NOT FREE TO MOVE TO THE ELECTRODES WHEN MOLTEN, THE IONS HAVE MORE FREEDOM AND CAN MOVE SODIUM IONS GO TO THE CATHODE AND EACH PICK UP AN ELECTRON Na+ + e- Na

  26. ELECTROLYSIS OF SODIUM CHLORIDE SOLID SODIUM CHLORIDE DOES NOT CONDUCT ELECTRICITY BECAUSE THE IONS ARE NOT FREE TO MOVE TO THE ELECTRODES WHEN MOLTEN, THE IONS HAVE MORE FREEDOM AND CAN MOVE SODIUM IONS GO TO THE CATHODE AND EACH PICK UP AN ELECTRON Na+ + e- Na CHLORIDE IONS GO TO THE ANODE AND EACH GIVE UP AN ELECTRON Cl- Cl + e- 2Cl- Cl2 + 2e-

  27. ELECTROLYSIS OF SODIUM CHLORIDE SOLID SODIUM CHLORIDE DOES NOT CONDUCT ELECTRICITY BECAUSE THE IONS ARE NOT FREE TO MOVE TO THE ELECTRODES WHEN MOLTEN, THE IONS HAVE MORE FREEDOM AND CAN MOVE SODIUM IONS GO TO THE CATHODE AND EACH PICK UP AN ELECTRON Na+ + e- Na CHLORIDE IONS GO TO THE ANODE AND EACH GIVE UP AN ELECTRON Cl- Cl + e- 2Cl- Cl2 + 2e-

  28. ELECTROLYSIS OF SODIUM CHLORIDE SUMMARY SOLID SODIUM CHLORIDE DOES NOT CONDUCT ELECTRICITY BECAUSE THE IONS ARE NOT FREE TO MOVE TO THE ELECTRODES WHEN MOLTEN, THE IONS HAVE MORE FREEDOM AND CAN MOVE SODIUM IONS GO TO THE CATHODE AND EACH PICK UP AN ELECTRON Na+ + e- Na CHLORIDE IONS GO TO THE ANODE AND EACH GIVE UP AN ELECTRON Cl- Cl + e- 2Cl- Cl2 + 2e-

  29. ELECTROLYSIS OF AQUEOUS SODIUM CHLORIDE (BRINE)

  30. ELECTROLYSIS OF BRINE WHEN SODIUM CHLORIDE DISSOLVES IN WATER, THE IONS SEPARATE

  31. ELECTROLYSIS OF BRINE WHEN SODIUM CHLORIDE DISSOLVES IN WATER, THE IONS SEPARATE WATER CONTAINS A FEW IONS

  32. ELECTROLYSIS OF BRINE WHEN SODIUM CHLORIDE DISSOLVES IN WATER, THE IONS SEPARATE WATER CONTAINS A FEW IONS POSITIVE IONS ARE ATTRACTED TO THE NEGATIVE CATHODE...

  33. ELECTROLYSIS OF BRINE WHEN SODIUM CHLORIDE DISSOLVES IN WATER, THE IONS SEPARATE WATER CONTAINS A FEW IONS POSITIVE IONS ARE ATTRACTED TO THE NEGATIVE CATHODE... OF THE TWO, HYDROGEN IONS ARE PREFERRED

  34. ELECTROLYSIS OF BRINE WHEN SODIUM CHLORIDE DISSOLVES IN WATER, THE IONS SEPARATE WATER CONTAINS A FEW IONS POSITIVE IONS ARE ATTRACTED TO THE NEGATIVE CATHODE... OF THE TWO, HYDROGEN IONS ARE PREFERRED NEGATIVE IONS ARE ATTRACTED TO THE POSITIVE ANODE...

  35. ELECTROLYSIS OF BRINE WHEN SODIUM CHLORIDE DISSOLVES IN WATER, THE IONS SEPARATE WATER CONTAINS A FEW IONS POSITIVE IONS ARE ATTRACTED TO THE NEGATIVE CATHODE... OF THE TWO, HYDROGEN IONS ARE PREFERRED NEGATIVE IONS ARE ATTRACTED TO THE POSITIVE ANODE... OF THE TWO, CHLORIDE IONS ARE PREFERRED

  36. ELECTROLYSIS OF BRINE AT THE NEGATIVE CATHODE HYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS H+ + e- H

  37. ELECTROLYSIS OF BRINE AT THE NEGATIVE CATHODE HYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS H+ + e- H 2H+ + 2e- H2 The atoms form molecules and hydrogen gas H2 is produced

  38. ELECTROLYSIS OF BRINE AT THE NEGATIVE CATHODE HYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS H+ + e- H 2H+ + 2e- H2 AT THE POSITIVE ANODE CHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS Cl- Cl + e-

  39. ELECTROLYSIS OF BRINE AT THE NEGATIVE CATHODE HYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS H+ + e- H 2H+ + 2e- H2 AT THE POSITIVE ANODE CHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS Cl- Cl + e- 2Cl- Cl2 + 2e- The atoms form molecules and chlorine gas Cl2 is produced

  40. ELECTROLYSIS OF BRINE AT THE NEGATIVE CATHODE HYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS H+ + e- H 2H+ + 2e- H2 AT THE POSITIVE ANODE CHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS Cl- Cl + e- 2Cl- Cl2 + 2e- SODIUM HYDROXIDE SOLUTION REMAINS

  41. ELECTROLYSIS OF BRINE AT THE NEGATIVE CATHODE HYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS H+ + e- H 2H+ + 2e- H2 AT THE POSITIVE ANODE CHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS Cl- Cl + e- 2Cl- Cl2 + 2e- SODIUM HYDROXIDE SOLUTION REMAINS

  42. ELECTROLYSIS OF BRINE SUMMARY AT THE NEGATIVE CATHODE HYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS H+ + e- H 2H+ + 2e- H2 AT THE POSITIVE ANODE CHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS Cl- Cl + e- 2Cl- Cl2 + 2e- SODIUM HYDROXIDE SOLUTION REMAINS

  43. INDUSTRIAL ELECTROLYSIS OF BRINE

  44. SODIUM CHLORIDE THE DIAPHRAGM CELL CHLORINE GAS HYDROGEN GAS BRINE IONS IONS SODIUM HYDROXIDE SOLUTION (CAUSTIC SODA) DIAPHRAGM STOPS CHLORINE MIXING WITH SODIUM HYDROXIDE

  45. THE DIAPHRAGM CELL IMPORTANT ASPECTS CHLORINE HYDROGEN BRINE IONS IONS SODIUM HYDROXIDE (CAUSTIC SODA) DIAPHRAGM WHAT IS AN ADVANTAGE OF ELECTROLYSING BRINE RATHER THAN MOLTEN SODIUM CHLORIDE?

  46. THE DIAPHRAGM CELL IMPORTANT ASPECTS CHLORINE HYDROGEN BRINE IONS IONS SODIUM HYDROXIDE (CAUSTIC SODA) DIAPHRAGM WHAT IS AN ADVANTAGE OF ELECTROLYSING BRINE RATHER THAN MOLTEN SODIUM CHLORIDE? LESS ENERGY IS NEEDED BECAUSE YOU DON’T HAVE TO MELT THE SODIUM CHLORIDE; IT HAS A HIGH MELTING POINT

  47. THE DIAPHRAGM CELL IMPORTANT ASPECTS CHLORINE HYDROGEN BRINE IONS IONS SODIUM HYDROXIDE (CAUSTIC SODA) DIAPHRAGM WHAT HAPPENS AT THE POSITIVE ANODE?

  48. THE DIAPHRAGM CELL IMPORTANT ASPECTS CHLORINE HYDROGEN BRINE IONS IONS SODIUM HYDROXIDE (CAUSTIC SODA) DIAPHRAGM WHAT HAPPENS AT THE POSITIVE ANODE? CHLORIDE IONS ARE OXIDISED Cl¯ – e¯ Cl 2Cl¯ – 2e¯ Cl2

  49. THE DIAPHRAGM CELL IMPORTANT ASPECTS CHLORINE HYDROGEN BRINE IONS IONS SODIUM HYDROXIDE (CAUSTIC SODA) DIAPHRAGM WHAT HAPPENS AT THE NEGATIVE CATHODE?

  50. THE DIAPHRAGM CELL IMPORTANT ASPECTS CHLORINE HYDROGEN BRINE IONS IONS SODIUM HYDROXIDE (CAUSTIC SODA) DIAPHRAGM WHAT HAPPENS AT THE NEGATIVE CATHODE? HYDROGEN IONS ARE REDUCED H+ + e¯ H 2H+ + 2e¯ H2

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