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TitleChemistry Lab Report 1
TagsRedox Electrode Electrolyte Anode Cathode
File Size196.5 KB
Total Pages9
Document Text Contents
Page 1


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There are three types of electrolyte:

 Strong electrolyte: dissociate or ionizes completely or almost completely
to form free mobile ions in the aqueous or molten state.

 Weak electrolyte: ionizes or dissociates only partially to form free
mobile ions. Most of the electrolyte remains as un-ionised molecules.

 Non-electrolyte: does not ionise at all in solution and thus current does
not flow through such solution.

In order to ionize, the aqueous electrolyte which contain hydrogen and
hydroxide ions as well as the ions of the solute compete with each other at the

The ions that are successfully released at the electrodes depend on three


1. The position of the ion in the electrochemical series

2. The concentration of the ion in the solution

3. The nature of the electrode


 Batteries (6V)

 Connecting wires with crocodile clips

 Ammeter

 Rheostat

 Beaker 250 ml

 1M copper (II) sulphate solution

 Copper strips

 Acetone

 Distilled water

 Electronic balance

 Stop watch

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 Electrolysis of copper II sulphate solution using copper electrodes

(participating electrodes)

The ions present in the solution are:

copper ions chloride ions hydrogen ions hydroxide ions



H+ OH-

At the cathode,

The positive ions are attracted to the negative cathode. There is

competition between the copper ions and the hydrogen ions. As the

hydrogen ion or hydrogen redox equilibrium appears higher in the

electrochemical series than the copper ion or copper equilibrium, the

copper ions are preferentially reduced and copper metal is deposited at the

electrode. A brown layer deposited at the cathode is observed.


+ 2e Cu

Copper(II) sulphate


Copper electrodes

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After the electrolytic cell is switched off, the copper cathode are

taken out and weighed. There is significant change in the mass of the

cathode before and after the reaction. The mass increased by 0.16g. This

increase and the brown colour shows that there is copper metal deposited at

the cathode.

At the anode,

In this case, the electrode is made of copper and it is easier for the

copper to dissolve leaving its electrons behind on the anode than for any

other ion to be released.

Cu Cu

+ 2e

After the electrolytic cell is switched off, the copper anode is taken

out and weighed. There is significant change in the mass of the anode

before and after the reaction. The mass decreased by 0.21g. This shows that

there is copper metal loss at the anode as it has been oxidized to form

copper(II) ions. The ions released are now motile in the copper(II) sulphate


In short, copper is deposited at the cathode and is dissolved at the anode.


+ Cu Cu + Cu

Consequently the concentration of copper ions in solution remains

constant as the rate of ionization of copper atom and the rate of reduction of 

copper(II) ion is the same. That is why there is no significant change in the blue

colour of copper(II) sulphate solution at the beginning and the end of 


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