Chemistry- Electrolysis

Breif notes on electrolysis!

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When an ionic substance is melted or dissolved in water (a solution has formed) the ions are free to move about within the liquid or solution.

Aluminium and copper are examples of metals purified by electrolysis.

During electrolysis, +Chargd electrons are attracted to the -Charged electrode (Cathode)
And -Charged ions move to the +Charged electrode (Anode).

The electrolysis of sodium chloride produces hydrogen, sodium hydroxide and chlorine.
These three substances can be made;

Chlorine; Kills bacteria, used in cleaning products, used to clean pool water. Bleach is made by reacting chlorine with sodium hydroxide, also some plastics such as PVC can be   made.
Hydrogen; Hydrogenation, it can be sued to form other chemicals like ammonia.
Sodium hydroxide; Used to make soap, is in the manufacture of textiles paper & ceramics and can be used to purify aluminim in electrolysis.

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Electrolysis of molten ionic compounds


KI (Potassium Iodide)

Cathode;  Potassium
Anode;  Iodide

MgCl2 (Magnesium Chloride)

Cathode; Magnesium
Anode; Chloride 

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Cont... (Half equations)

Half equation for the electrolysis of PbBr2  (Lead Bromide)

At the cathode;  Pb2+  +  2electrons -----> Pb

The 2+ means lead needs to lose two electrons to have a full outer shell.

Solid lead forms and sinks to the bottom.

At the anode;   2Br-   ----->   Br2  +   2electrons

Br2 means there are two Br's, and the - means that the Br needs to gain an electron, since there are two Br's in the equation we add 2electrons. The 2 was put infront of the Br to balance the equation.

Bromine gas forms.

The overall equation is;     PbBr2-----> Pb+Br2

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Electrolysis of solutions

Example;    KI (Potassium Iodide)

Cathode;  Hydrogen forms here 
Anode;   Iodine forms here

Example;     H2SO4  (Sulfuric acid)

Cathode;   Hydrogen forms here
Anode;   Oxygen forms here

Negative electrode
If a solution contains ions of metals low in the reactivity series, the metal forms on the Cathode.
But if the solution contains metals high in the reactivity series, hydrogen forms here.

Positive electrode
If a solution contains halide ions (chloride, iodide ect.), these will form at the anode.
But if the solution contains other ions (nitrates ect.), oxygen forms here.

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Oil Rig

Remember this; 

O- Oxidation

I- Is

L- Losing

R- Reduction

I- Is

G- Gaining

The example on card three (to do with lead bromide) is an example of a REDOX reaction because both reduction and oxidation happened.

Oxidation happens at the negative electrode and reduction happens at the positive electrode.

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:) PurpleJaguar (: - Team GR

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hey could you please do another one for electrolytic cell? :)


hey its interesting topic could u please do us another one?

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