Electrolysis of copper sulphate

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Danny Aburas

Introduction
Electrolysis is referred to as the decomposition of a compound by applying a flow of electron current (electricity) into the solution. Electrolysis can only occur in solutions of electrolytes. Electrolytes are compounds that are able to conduct electricity when in a molten state or when dissolved in water. Electrolytes cannot conduct electricity when they are in a solid state as in this state the ions are held in a 3 dimensional lattice in which they cannot move, thus preventing the flow of electricity through the compound. If, however the compound is molten or dissolved in water, it’s component ions dissociate and are no longer held by this lattice thus, can move around and furthermore, meaning electrolysis can occur. Usually in electrolysis, something will be reduced (gain in e-) and something will be oxidized (loss of e-). Reduction takes place on the cathode (negative electrode) while oxidation occurs on the anode (positive electrode).


This particular experiment involves the electrolysis of copper (II) sulphate using a pair of copper electrodes. The copper electrodes are “active” meaning they take a part in the electrolysis. First, the electric current passed through the electrolytic cell will cause the copper sulphate solution to dissociate into it’s two component ions, Cu
2+ and SO42-. .The copper anode (+) will dissolve and fall into the copper (II) sulphate solution as Cu at the anode is being oxidized to Cu2+ by the newly dissociated SO42- ions and loses electrons, meanwhile, the Copper cathode will pick up Cu2+ ions and reduce them to Cu. Note that Hydrogen does not form at the cathode because copper is lower in the reactivity series and more eager to gain electrons than exist as an ion the solution.

Half reactions
 
At the Cathode (-), Cu
2+ ions are reduced to Cu by the gain of electrons: Cu2++ 2e-  Cu
At the anode (+), Cu is oxidized to Cu
2+ ions by loss of electrons to the cathode: Cu Cu2 + 2e-

Aim/purpose: The purpose of this experiment is to investigate the relationship between quantity of current applied and the mass of substance formed on the cathode.

Hypothesis: It is hypothesised that if the current increases then mass deposited on the cathode will increase at a proportional rate.

Variables

Independent – Magnitude of Current flowing into the electrolytic cells.

Dependent – Mass of Copper deposited at the cathode after electrolysis (g)

Controlled Variables: These variables affect the experiment results and should be controlled by being kept constant throughout the experiment to gain a reliable result.


- Concentration of Copper (II) Sulphate solution. 
The higher the concentration of
Copper (II) Sulphate solution, The more ions there are in the solution, consequently, the more likely chance of collisions at the cathode occur and to form more copper. 

- Time of current flow

Time is a crucial variable in this experiment and will need to be controlled critically. The longer the time aloud for current to pass through the electrolytic cell, the more electrons there are being fed into the cell, meaning more electrons are reducing copper ions to form solid copper on the cathode.


- Distance between electrodes.

Distance between the electrodes should be kept constant. In theory, the closer the distance between the  electrode pairs,  the quicker the rate of electrolysis occurs. This is as the current would flow through the electrodes faster, therefore increasing the rate of electrolysis, consequently, increasing the mass of Cu deposited on the cathode.


- Surface Area of Electrodes.

The greater the surface area of the electrodes, the greater the amount of Cu 2+ ions lost at the anode and gained at the cathode. This is because with a larger surface area, there is more chance of a collision occurring to form more copper at the cathode as more particles are available for collision.

Apparatus & Chemicals

Safety
This experiment is relatively safe to perform if the necessary precautions are met, the following safety measures are necessary for your protection.

  • Copper sulphate may cause irritation if contact with the eye or skin occurs, therefore, for your safety, eye protection must be worn to act as a barrier preventing contact as well as an apron to avoid contact with skin or clothes as copper sulphate can stain.
  • Copper sulphate is harmful if swallowed, do not drink, it does not taste very good believe me.
  • The electric current being used is not high enough to cause a fatal electrocution when touched, however electric shocks do hurt so do not touch both terminals while the electricity is on. Also, sparks could cause a fire therefore care must be taken nothing flammable is in the vicinity.
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Method

  1. The Setup
  1. Collect all required equipment.
  2. Clean the 10 copper electrodes thoroughly using sandpaper to remove impurities that could inhibit electrolysis.
  3. Assign half of the electrodes to be the anodes and mark them with A1 to A5 using a permanent marker, then the other half will be the cathodes, mark these with C1 to C5(there should be 5 C’s and 5 A’s). Be sure not to write on the side that will go into the solution as this could inhibit oxidation or reduction!
  4. Weigh the cathodes using the electronic balance and record ...

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