Basics and Copper Chloride

Electrolysis is where electricity is passed through an electrolyte which is either a molten or aqueous ionic compound so that ions are free to move

The cations are either metals or hydrogen and the anions are the non metals

If the anion is nitrate or sulphate then the hydroxide ion is attracted to the anode

Copper Chloride Solution

Method:

Half fill the beaker with the solution

Connect the electrodes in a simple circuit with the power pack and lamp

Start the current and observe what happens at the cathode (negative) and anode (positive)

Observations:

Cathode - Bubbling (Chlorine gas)

Anode - Coating of copper onto electrode

Half Equations:

Cathode - Cu + 2e- → Cu

Anode - 2Cl → Cl2 + 2e-

Electrolysis of Brine

Brine is aqueous sodium chloride (NaCl)

Observations:

Cathode - Bubbling, blue (cause by universal indicator)

Anode - Bubbling, colourless

Cathode - Hydrogen is produced and sodium hydroxide solution is formed (this is an alkali and what causes the blue colour)

Half Equation : 2H+ + 2e- → H2

Anode - Chlorine is produced which bleaches the colour of the indicator

Half Equation : 2Cl- → Cl2 + 2e-

The least reactive cation goes to the cathode. Hydrogen ions are present in water and are less reactive than sodium, hydrogen goes to the cathode and sodium forms sodium hydroxide

Electrolysis of Aluminium

Aluminium oxide melts at over 2000 ^o

It is mixed with molten cryolite which lowers the melting point to 900

Cathode : Al3+ + 3e- → Al

Anode : 2O2- → O2 + 4e-

The oxygen reacts with the carbon anode and forms CO2 gas so the anode gets smaller and needs to be replaced regularly

Half Equations

Required Practical

Method:

1. Pour copper chloride solution into the beaker to about 50cm

2. Place the electrode assembly into the beaker, attach crocodile clips to the roads and connect to the power supply

3. Observe both electrodes and record results

4. Hold blue litmus paper over the beaker and record observations

5. Repeat steps using different solutions (copper sulphate, sodium chloride, sodium sulphate)

Chemical Cells and Batteries

Chemical cells convert energy released in chemical reactions into electricity. It can be made by connecting two different metals that are dipped into an electrolyte

Different metals will react differently with the same electrolyte which is what causes the charge difference or the voltage of the cell, the bigger difference in reactivity of the electrodes, the bigger the voltage of the cell. The electrolyte used in a cell will also affect the size of the voltage since different ions in solution will react differently with the metal electrodes used

In some cells the chemical reactions that happen are irreversible over time the reacting particles get used up and turned into products. Once any one of the reactants is used up the reaction can’t happen and so no electricity is produced and the products can’t be turned into the reactants so the cell can’t be recharged.

In a rechargeable the reaction can be reversed by connecting it to an external electric current

Fuel Cells

Fuel cells convert chemical energy into electricity. In a fuel cell a fuel reacts with oxygen or other oxidising agent to produce a potential difference. Fuel cells don’t store fuel so the fuel needs to be replenished from an external source when it’s been used.

Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment

At the negative electrode (the anode in this situation) hydrogen loses electrons to produce H+ ions this is oxidation, the H+ ions in the electrolyte move to the cathode

At the positive electrode (the cathode), oxygen gain electrons from the cathode and reacts with H+ ions to make water this is reduction

Half equations:

Anode : H2 → 2H+ + 2e-

Cathode : 4H+ + O2 + 4e- → 2H2O

(compared to a rechargeable battery)