Electrolysis Reactions (1 Viewer)

[amberbambi]

Hi guys

I just have a few qns regarding electrolysis reactions and how they correlate with galvanic cells (opposites of one another).

How are we meant to select the appropriate oxidation and reduction equations when writing electrolysis equations (e.g. a numerical basis in terms of volts required, reactivity)? Furthermore, what do we have to consider when there are aqueous solutions - both dilute and concentrated?

Thank you

 

[Drsoccerball]

Hi guys

I just have a few qns regarding electrolysis reactions and how they correlate with galvanic cells (opposites of one another).

How are we meant to select the appropriate oxidation and reduction equations when writing electrolysis equations (e.g. a numerical basis in terms of volts required, reactivity)? Furthermore, what do we have to consider when there are aqueous solutions - both dilute and concentrated?

Thank you

you can use the standard potential table at the back of the periodic table to show which one is oxidation and which ones reduction.
If the element is higher on the potential table then it is oxidation while the other one is reduction. Oxidation happens at the anode. Reduction happens at the cathode. OIL RIG Oxidation is loss of electrons Reduction is gain of electrons... Thats how you can tell which way to put the reaction

 

[Librah]

you can use the standard potential table at the back of the periodic table to show which one is oxidation and which ones reduction.
If the element is higher on the potential table then it is oxidation while the other one is reduction. Oxidation happens at the anode. Reduction happens at the cathode. OIL RIG Oxidation is loss of electrons Reduction is gain of electrons... Thats how you can tell which way to put the reaction

Electrolysis is different from reactions in galvanic cells.

 

[Librah]

OP. best to give an example, it's a bit confusing to explain.

 

[amberbambi]

An example: - The electrolysis of an aqueous solution of potassium chloride

 

[Librah]

An example: - The electrolysis of an aqueous solution of potassium chloride

H2O, K+ and Cl- are in the solution. Find all the possible reactions from the standard reduction table.You have to find out whether K+ or H2O will be preferentially reduced, and which of Cl- and H2O will be preferentially oxidized. To do this see which potential is "more positive."

Cl- oxidation is (-1.36V) H2O oxidation is (-1.23) So theoretically H2O should be oxidized when a minimum voltage is applied, however there's something called an over-potential (which is beyond the syllabus, but you can look this up), for certain reactions like this one, it's experimentally determined and usually unpredictable. So actually Cl2(g) is produced.

K+ reduction is (-2.94V), while H2O reduction is (-0.83) So water will be reduced when a minimum voltage is applied.