Tuesday, 22 March 2016

1.54 describe experiments to investigate electrolysis, using inert electrodes, of aqueous solutions such as sodium chloride, copper(II) sulphate and dilute sulphuric acid and predict the products

In aqueous solutions, as well as ions from the ionic compound, there will be hydrogen ions (H+) and hydroxide ions (OH-) from the water.

 Products

 At the cathode, if H+ ions and metal ions are present, hydrogen gas will be produced if the metal ions are more reactive than H+ ions (for example, sodium ions). If the metal ions are less reactive than the H+ ions (for example, copper ions), a solid layer of the pure metal will be produced.

 At the anode, if OH- and halide ions (Cl-, Br-, I-) are present, then molecules of chlorine, bromine or iodine will be formed. If no halide ions are present, then oxygen gas and water will be formed.

 Electrolysis of sulphuric acid
A solution of sulphuric acid (H2SO4) contains three different ions: SO42− , H+ and OH-.

 At the cathode: as sulphur (SO42−) is more reactive than hydrogen, hydrogen gas is produced...

 2H+ + 2e- ---> H2
At the anode: as there no halide ions present, oxygen and water is produced.

 4OH- ---> O2 + 2H2O + 4e-
Electrolysis of sodium chloride
A solution of sodium chloride (NaCl) contains four different ions: Na+, Cl-, OH- and H+

 At the cathode: as sodium is more reactive than hydrogen, hydrogen gas is produced...

 2H+ + 2e- ---> H2

 At the anode: as chlorine ions are present (halide), then chlorine atoms will be produced (as chlorine gas)...

 2Cl- ---> Cl2 + 2e-
Electrolysis of copper(II) sulfate
A solution of copper(II) sulphate (CuSO4) contains four different ions: Cu2+, SO42−, H+ and OH-.

 At the cathode: as copper is less reactive than hydrogen, copper metal is produced...

 Cu2+ + 2e- ---> Cu

 At the anode: as there are no halide ions present, oxygen and water are produced...

 4OH- ---> O2 + 2H2O + 4e-
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7 comments:

  1. saiyinie7 January 2017 at 05:06

    This comment has been removed by the author.

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  2. Haroon19 March 2017 at 10:34

    This was really useful for my revision. Much clearer explanation then my teacher. Thumbs up!

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  3. ESS10 April 2017 at 14:01

    Why would SO4 2- be attracted to the cathode?

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    1. Millie20 April 2017 at 12:38

      It's not:)) sorry if my explanations are a little unclear but basically because hydrogen is less reactive than sodium, the hydrogen is attracted to the cathode (which is why hydrogen gas is formed) - sorry for such a late reply! i managed to lock myself out of my account hahahah x

      Delete
  4. Unknown4 June 2017 at 09:16

    Millie he/she means that the ion is negative so why would it ever attract to the cathode in the first place. I dont understand this either.

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  5. Anonymous13 May 2018 at 06:31

    Hey, this is super helpful, but in the electrolysis of sulphuric acid, you wrote "sodium" instead of "sulphate". Just thought I'd point it out. This is a really helpful resource, thank you!

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