Electrolysis of Water & Hydrochloric Acid | Reactions | Chemistry | FuseSchool — Transcript

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1. 0:00[Music]
2. 0:02[Applause]
3. 0:02[Music]
4. 0:05the discovery that passing an electric
5. 0:08current through water would split apart
6. 0:10was made quite soon after the discovery
7. 0:13of current electricity itself this
8. 0:16predates Michael Faraday's work in this
9. 0:19area but it is he who introduced most of
10. 0:22the terms that we still use today
11. 0:24electrolysis was named by Faraday though
12. 0:28not an exact translation it means to use
13. 0:31electricity to split something apart
14. 0:33let's remind ourselves of the equipment
15. 0:36that we use in electrolysis almost all
16. 0:39of which was named by Faraday the cell
17. 0:42has a positive anode and a negative
18. 0:45cathode the electrodes connected to the
19. 0:48cell have the same name and charge the
20. 0:51liquid being electrolyzed is the
21. 0:53electrolyte pure water is a very poor
22. 0:57conductor of electricity as free ions
23. 1:00charged species are needed to carry
24. 1:03current in the solution but water
25. 1:05remember is a covalent molecule and at
26. 1:09room temperature
27. 1:10hardly ionizes and so the concentration
28. 1:13of the ions formed is extremely small
29. 1:16pure water acts as an insulator at safe
30. 1:20voltages if however we add a little
31. 1:23sulfuric acid to water this greatly
32. 1:26increases the ability of water to
33. 1:28undergo electrolysis without altering
34. 1:30the products obtained if we use
35. 1:33electrolysis we will see bubbles forming
36. 1:36around both electrodes the most around
37. 1:39the cathode if we use a Hofmann
38. 1:41voltammeter we can collect the gases
39. 1:44made by each electrode the gases are
40. 1:47made in a ratio of two to one but the
41. 1:50initial solubility of oxygen in the
42. 1:52water sometimes masks this testing each
43. 1:55gas is the usual way we'll confirm their
44. 1:58identity let us look closely at what's
45. 2:02happening the ions present in water will
46. 2:05be the hydrogen ion and the hydroxide
47. 2:09ion these ions will be attracted to
48. 2:13the electrode with the opposite charge
49. 2:16to use Faraday's own words I propose to
50. 2:19distinguish these bodies by calling
51. 2:22those anions which go to the anode and
52. 2:25those passing the cathode cations at the
53. 2:33anode we see oxygen being made this is a
54. 2:36loss of electrons which go into the
55. 2:38anode and so is an oxidation reaction at
56. 2:41the cathode we see hydrogen being made
57. 2:44the electrons gained are provided by the
58. 2:47cathode this is a reduction reaction
59. 2:50combining both reactions that are taking
60. 2:52place simultaneously we get a redox
61. 2:55reaction notice that the balanced
62. 2:58equation gives the gases a two to one
63. 3:00ratio
64. 3:02remember oil-rig as a way of tracking
65. 3:05electrons in a redox reaction if water
66. 3:09is acidified with a hydrochloric acid
67. 3:11the reaction is altered due to the
68. 3:14presence of the chloride ions cl- in
69. 3:18this case it's the chloride anions that
70. 3:21are oxidized and not the hydroxide ions
71. 3:24so chlorine and not oxygen is made at
72. 3:27the anode the combined reaction is again
73. 3:30a redox with the gases each being made
74. 3:33in equal amounts as chlorine is very
75. 3:38much more soluble in water than hydrogen
76. 3:41is it will take a while for the water to
77. 3:44become saturated enough to enable any
78. 3:46appreciable amount of gas to be seen and
79. 3:49while you're working with it in the lab
80. 3:52remember chlorine is toxic so take
81. 3:55precautions next