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Electrolysis of Solutions

Electrolysis of Solutions. Al. Al 3+. What is electrolysis?. Electrolysis involves breaking down ionic substances into simpler substances using electricity.

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Electrolysis of Solutions

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  1. Electrolysis of Solutions

  2. Al Al3+ What is electrolysis? Electrolysis involves breaking down ionic substances into simpler substances using electricity. An ionic substance contains charged particles called ions. An ion is an atom that has gained or lost electrons and so carries a positive or negative charge, which is shown after its formula. Aluminium atom loses 3 electrons Aluminium ion Ions with a positive charge have lost electrons, and ions with a negative charge have gained electrons. In electrolysis, the ionic substance must be dissolved in water or melted so that the ions are free to move.

  3. heat Oxidation and reduction In electrolysis, the substance that the current passes through and splits up is called the electrolyte. The electrolyte contains positive and negative ions. What happens to these ions during electrolysis? Negative ions move to the positive electrode and lose electrons. This is oxidation. Positive ions move to the negative electrode and gain electrons. This isreduction.

  4. Oxidation Is Loss of electrons ReductionIs Gain of electrons  magnesium + oxygen magnesium oxide +  2Mg(s) O2 (g) 2MgO(s) reduction: O2 + 4e-2O2- oxidation: Mg Mg2+ + 2e-   OILRIG An easy way to remember what happens to the electrons during oxidation and reduction is to think OILRIG: Equations written to show what happens to electrons during oxidation and reduction are called half-equations.

  5. Sodium chloride solution The electrolysis of sodium chloridesolution (NaCl solution), produces three very useful products: • chlorine (Cl2) • hydrogen (H2) • sodium hydroxide (NaOH). Chlorine is expected as a product of this process, but hydrogen and sodium hydroxide are less expected. Sodium chloride solution is more commonly known as brine.

  6. Electrolysis of NaCl solution

  7. The positive electrode

  8. The negative electrode

  9. Uses of Cl2, H2 and NaOH

  10. This is because sodium chloride solution also contains H+ ions from some of the water:H2O (l) H+ (aq) + OH- (aq).  For all ionic compounds containing a metal that is more reactive than hydrogen, electrolysis of a solution of the compound will produce hydrogen rather than the metal. Why is sodium not formed? In the electrolysis of sodium chloride solution,the Na+ions might be expected to form sodium at the negative electrode. Instead, hydrogen gas is produced here. At the negative electrode, H+ ions compete with Na+ions. The H+ ions gain electrons; the Na+ ions stay in solution.

  11. 2NaCl (aq) + 2H2O (l) H2 (g) + Cl2 (g) + 2NaOH (aq)  How does sodium hydroxide form? Sodium chloride solution has four types of ions: • Na+ and Cl- ions from the sodium chloride • H+ and OH- ions from the water. The Cl- ions form chlorine at the positive electrode and the H+ ions form hydrogen at the negative electrode. Na+ and OH- ions are left behind, and so a solution of sodium hydroxide(NaOH)is formed. What is the overall equation for the electrolysis of brine?

  12. Environmental concerns The industrial electrolysis of brine does have some environmental implications, including concerns about the large amount of electricity used by the process. In addition, chlorine, a product of the electrolysis of brine, is toxic. Its large- scale manufacture can lead to hazards. Electrodes used to be made from highly toxic mercury and asbestos, which could contaminate water supplies.

  13. Fill in the gaps

  14. Water is a covalent compound and so is a poor conductor of electricity. However, it does contain a few free H+ and OH- ions: H2O (l) H+ (aq) + OH- (aq).  Splitting water by electrolysis Electrolysis can be used to splitwater(H2O) into its elements, hydrogen (H2)and oxygen (O). The conductivity of water can be improved by adding an acid, such as dilute sulfuric or hydrochloric acid. This releases more ions so that more current flows during electrolysis, which creates hydrogen and oxygen.

  15. Using hydrochloric acid

  16. At the negative electrode: 2H+ + 2e- H2(reduction)  At the positive electrode: 4OH- 2H2O+ O2 + 4e-(oxidation)  2H2O (l)2H2(g) + O2 (g)  Redox equations What happens at the electrodes during the electrolysis of water? What is the overall equation for the electrolysis ofwater? Twice as much hydrogen forms as oxygen. Why is this?

  17. Glossary

  18. Anagrams

  19. Multiple-choice quiz

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