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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ReplyDeleteThis was really useful for my revision. Much clearer explanation then my teacher. Thumbs up!
ReplyDeleteHaroon Baksh?
DeleteWhy would SO4 2- be attracted to the cathode?
ReplyDeleteIt'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
DeleteMillie 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.
ReplyDeleteHey, 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!
ReplyDelete