Investigate how the rate of electrolysis is affected when changing the current in the circuit.

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Electrolysis

When chemical compounds are in a molten state, or if they are dissolved in water or other liquids their molecules become “separates into positively and negatively charged components, which have the conduct electricity”, or they become ionized

Electrolysis is the process of breaking down or ‘decomposing’ a compound, by running an electric current through a chemical compound when it is ionized.  This is done using a simple circuit, as below:

                                                                           

                                                                         

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When a pair of electrodes as above is placed in an ionized solution (Electrolyte) and there is a current flowing between them, the positive ions move toward the negative electrode - cathode and the negative ions move towards the positive electrode - anode.  The ions that move towards the cathode are called “cations” and the ions that move toward the anode are called “anions”. When the ions reach their respective electrodes, they gain or lose electrons and are transformed into neutral atoms.

Electrolysis of molten lead bromide:

As is above, the ions gain or lose electrons at the electrodes.  These reactions can be shown using “Half – Equation”.  Below, I have shown them using the example of Lead Bromide.

The lead bromide is separated into molten lead and Bromide.
PbBr(l)             Pb(l) + Br²(g)


When lead Bromide is melted, the ions are free to move towards the oppositely charged electrode, because Lead Bromide is an ionic substance.

When the positive lead ions move to the negative electrode, they gain electrons in a reduction reaction:  Pb²+  +  2e-                     Pb

In the same way when the negative bromide ions move to the positive electrode they lose electrons in an oxidation reaction
2Br-  -  2e-                      Br²

Sometimes oxidation reactions are written with “+2e-“  on the left.

In such instances the alternative half equation is:
2Br-             Br² + 2e-


Electrolysis – How Does It Happen?
A compound made from metal and non-metal has ions which cannot move freely.  This means the compound cannot conduct electricity, nor can it move towards electrodes.  This is why the electrolyte must be in liquid form – either by melting it or by dissolving it in water.  When they are in liquid form the ions are free to move around.  This enables them to conduct electricity and to move towards the electrodes.

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Metal ions are positive and non-metal ions are negative.  We know that opposite charges attract, there fore the metal ions would be attracted to the negative electrode – The cathode – and the metal ions would be attracted to the positive electrode  - The anode.  For this reason we call the metal ions “cations” (from ‘Cathode’) and the non-metal ions “anions” (from ‘Anode’).

We know that the amount of electricity in the circuit affects the rate of electrolysis, as Faraday says in his first law that the amount of electricity in the circuit is directly proportional to the rate of ...

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