6.3 (a) electrolysis of an aqueous solution

18,432 views

Published on

Published in: Technology, Business
2 Comments
4 Likes
Statistics
Notes
No Downloads
Views
Total views
18,432
On SlideShare
0
From Embeds
0
Number of Embeds
600
Actions
Shares
0
Downloads
274
Comments
2
Likes
4
Embeds 0
No embeds

No notes for slide

6.3 (a) electrolysis of an aqueous solution

  1. 1. ELECTROLYSIS OF AN AQUEOUS SOLUTION
  2. 2. <ul><li>In the electrolysis of aqueous solutions only one ion is involved in the selective discharge of ions at each electrode during the electrolysis and their ions are free to move. </li></ul><ul><li>Their ions are cation and anion. </li></ul>
  3. 3. H + NO 3 - , OH- Aqueous Solution Salt Ionization Water Ionization Cation Anion NaCl(aq) NaCl Na + + OH- H 2 O H + + OH- Na + , H + Cl-, OH- CuSO 4 (aq) CuSO 4 Cu 2+ + SO 4 2- H 2 O H + + OH- Cu 2+ , H + SO 4 2- , OH- HNO 3 (aq) HNO 3 H + + NO 3 - H 2 O H + + OH-
  4. 4. <ul><li>The positive ions are attracted to the negative electrode </li></ul><ul><li>The negative ions are attracted to the positive electrode </li></ul>Na + Na + Na + OH- OH- OH- NaCl Solution Carbon Electrode
  5. 5. <ul><li>The ion which is selected for discharge at an electrode depends on a number of factors, that is: </li></ul><ul><li>Position of the ions in the electrochemical series </li></ul><ul><li>Nature of the electrode </li></ul><ul><li>Concentration of the ions in solution </li></ul>
  6. 6. Position of the ions in the electrochemical series The figure below shows an idealized drawing of a cell in which an aqueous solution of sodium sulphate is electrolyzed Na 2 SO 4 OH- O 2 (g) SO 4 2- H + Na +
  7. 7. Observation Conclusion + Chemical Equation Anode(+): Ion OH- <ul><li>OH- ion much easier to discharge than SO 4 2- ion in the electrochemical series. </li></ul><ul><li>The only product formed is oxygen gas. </li></ul><ul><li>4OH - (aq) H 2 O (aq) + O 2(g) + 4e- </li></ul>Cathode(-): Ion H + <ul><li>H + ion much easier to discharge than Na + ion, the only product formed at the anode is hydrogen gas. </li></ul><ul><li>2H + (aq) +2e- H 2(g) </li></ul>
  8. 8. Electrochemical Series <ul><li>Li + </li></ul><ul><li>Na + </li></ul><ul><li>Mg 2+ </li></ul><ul><li>Al 3+ </li></ul><ul><li>Zn 2+ </li></ul><ul><li>Fe 2+ </li></ul><ul><li>Sn 2+ </li></ul><ul><li>Pb 2+ </li></ul><ul><li>H + </li></ul><ul><li>Cu 2+ </li></ul><ul><li>Hg + </li></ul><ul><li>Ag + </li></ul>F- SO 4 2 - NO 3 - Cl- Br- I- OH- The tendency of cation to discharge increases The tendency of anion to discharge increases
  9. 9. Nature of the Electrode Electrolysis of an aqueous solution of Cuprum Sulphate: Carbon Electrode Cuprum Sulphate Solution Carbon Electrode Anode Cathode
  10. 10. Observation Conclusion + Chemical Equation Anode(+): Ion OH- <ul><li>OH- ion much easier to discharge than SO 4 2- ion in the electrochemical series. </li></ul><ul><li>The only product formed is oxygen gas. </li></ul><ul><li>4OH - (aq) H 2 O (aq) + O 2(g) 4e- </li></ul>Cathode(-): Ion Cu 2+ <ul><li>Cu 2+ much easier to discharge than H + ion, the only product formed at the cathode is precipitate of brown colored. </li></ul><ul><li>Metal copper formed. </li></ul><ul><li>Cu 2+ (aq) + 2e- Cu (s) </li></ul>
  11. 11. Electrolysis of an aqueous solution of Cuprum Sulphate: Cuprum Electrode Cuprum sulphate Solution Cuprum Electrode cathode Anode
  12. 12. Observation Conclusion + Chemical Equation <ul><li>Anode(+): </li></ul><ul><li>Transfer of copper metal from the anode to the cathode during electrolysis. The copper sulphate is ionized in aqueous solution. </li></ul><ul><li>Each copper atom loses two electrons to become copper ions, which go into solution. </li></ul><ul><li>Cu (p) Cu 2+ (aq) + 2e- </li></ul><ul><li>Cathode(-): </li></ul><ul><li>The positively charged copper ions migrate to the cathode. </li></ul><ul><li>Where each gains two electrons to become copper atoms that are deposited on the cathode. </li></ul><ul><li>Cu 2+ (aq) + 2e- Cu (p) </li></ul>
  13. 13. Concentration of the Ions in Solution KI dilute O 2 (g) Electrode Carbon Electrode Carbon OH- Electrolysis of an aqueous solution of Dilute Potassium Iodide K + I- H +
  14. 14. Observation Conclusion + Chemical Equation Anode(+): Ion OH- <ul><li>OH- ion much easier to discharge than I- ion. </li></ul><ul><li>The only product formed at the anode is oxygen gas. </li></ul><ul><li>4OH - (aq) H 2 O (aq) + O 2(g) 4e- </li></ul>Cathode(-): Ion H + <ul><li>H + ion much easier to discharge than K + ion. </li></ul><ul><li>The only product formed at the anode is hydrogen gas. </li></ul><ul><li>2H + (aq) + 2e- H 2(g) </li></ul>
  15. 15. Electrolysis of an aqueous solution of Concentrated Potassium Iodide Electrode Carbon Electrode Carbon KI I- I 2 (g) H + OH- K +
  16. 16. Observation Conclusion + Chemical Equation Anode(+): Ion I- <ul><li>I- ion much easier to discharge than OH- ion because concentration of iodide ion is high. </li></ul><ul><li>Iodine gas formed. </li></ul><ul><li>2I- (aq) I 2(g) + 2e- </li></ul>Cathode(-): Ion H + <ul><li>H + ion much easier to discharge than K + ion. </li></ul><ul><li>The only product formed at the anode is hydrogen gas. </li></ul><ul><li>2H + (aq) +2e- H 2(g) </li></ul>
  17. 17. Activity 1
  18. 18. Anode Cathode Electrolyte Electrode Attracted Ion Ionized Ion Product Attracted Ion Ionized Ion Product NaCl (aq) Dilute Carbon Ions Cl-, OH- Ion OH- O 2 gas Ions Na + , H + Ion H + H 2 gas KCL (aq) Concentrated Carbon Ions Cl-, OH- Ion Cl- Cl 2 gas Ions K + , H + Ion H + H 2 gas CuBr 2 (aq) Dilute Carbon Ions Br-, OH- Ion OH- O 2 gas Ions Cu 2+ , H + Ion Cu 2+ Copper metal AgBr 2 (aq) Concentrated Carbon Ions Br-, OH- Ion Br- Br 2 gas Ion Ag + , H + Ion Ag + Argentum metal NiCl 2 (aq) Dilute Nikel Ions Cl-, OH- Metal nikel erode Ion Ni 2+ Ion Ni 2+ , H + Ion H + H 2 gas

×