Describe Electrolysis of an aqueous solution

Example 1:    Electrolyte   : Silver bromide, AgBr solution,
              C...
Example 2:      Electrolyte   : Copper(II) sulphate, CuSO4 solution,
                Concentration : 0.1 mol dm-3 ,
      ...
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Describe electrolysis of an aqueous solution

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Describe electrolysis of an aqueous solution

  1. 1. Describe Electrolysis of an aqueous solution Example 1: Electrolyte : Silver bromide, AgBr solution, Concentration : 2.0 mol dm-3 , Electrodes : carbon 1) Silver bromide, AgBr solution consists of Ag+ ions, H+ ions, Br - ions and OH- ions that move freely. 2) During electrolysis, the cations Ag+ ions and H+ ions move to the cathode; the anions Br - ions and OH- ions move to the anode. 3) At CATHODE, Silver, Ag+ ions are selectively discharged by receiving electrons to form Ag atom. This is because Ag+ ions has a lower position than H+ ions in the electrochemical series. Ag+ (aq) + e- → Ag (s) A silvery grey solid is deposited at cathode. Silver, Ag metal is formed at the cathode. 4) At ANODE, Bromide, Br - ions are selectively discharged by donating electrons to form Br2 molecules. This is because Br – ion has higher concentration in the electrolyte (even though Br - ions has a higher position than OH- ions in the electrochemical series.) Br - (aq) → Br2 (g) + 2e- Brown vapour is released at anode. Bromine, Br2 gas are produced at the anode. 5) Overall equation: { Ag+ + e- → Ag } x2 : 2Ag2+ + 2 e- → 2Ag 2Br - → Br2 + 2 e- 2Ag+ + 2Br - → 2Ag + Br2 * Homework: Describe Electrolysis of an aqueous solution Electrolyte : copper (II) chloride, CuCl2 solution Concentration : 0.1 mol dm-3 , Electrodes : carbon
  2. 2. Example 2: Electrolyte : Copper(II) sulphate, CuSO4 solution, Concentration : 0.1 mol dm-3 , Electrodes : carbon 6) Copper(II) sulphate, CuSO4 solution consists of Cu2+ ions, H+ ions, SO42- ions and OH- ions that move freely. 7) During electrolysis, the cations Cu2+ ions and H+ ions move to the cathode; the anions SO42- ions and OH- ions move to the anode. 8) At CATHODE, Copper (II), Cu2+ ions are selectively discharged by receiving electrons to form Cu atom. This is because Cu2+ ions has a lower position than H+ ions in the electrochemical series. Cu2+ (aq) + 2 e- → Cu (s) A brown solid is deposited at cathode. Copper, Cu metal is formed at the cathode. 9) At ANODE, Hydroxide, OH- ions are selectively discharged by donating electrons to form O2 and H2O molecules. This is because OH- ions has a lower position than SO42- ions in the electrochemical series. 4OH- (aq) → O2 (g) + 2H2O(l) + 4 e- Colourless gas bubbles are released at anode. (The gas relights a glowing wooden splinter.) Oxygen, O2 gas and water, H2O are produced at the anode. 10) Overall equation: { Cu2+ + 2 e- → Cu } x2 : 2Cu2+ + 4 e- → 2Cu 4OH- → O2 + 2H2O+ 4 e- 2Cu2+ + 4OH- → 2Cu + O2 + H2O

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