1. Electrolysis
Noadswood Science, 2012

2. Electrolysis To understand electrolysis and products it makes
Wednesday, April 26, 2017
Electrolysis
To understand electrolysis and products it makes

3. Ionic
Ionic substances form when a metal reacts with a non-metal – they contain charged particles called ions
For example, sodium chloride forms when sodium reacts with chlorine – it contains positively charged sodium ions and negatively charged chloride ions
Ionic substances can be broken down by electricity

4. Electrolysis
Electrolysis is the process by which ionic substances are decomposed (broken down) into simpler substances when an electric current is passed through them
For electrolysis to work, the ions must be free to move – ions are free to move when an ionic substance is dissolved in water or molten
For example, if electricity is passed through copper chloride solution, the copper chloride is broken down to form copper metal and chlorine gas…

5. Electrolysis
Positively charged ions move to the negative electrode during electrolysis – they receive electrons and are reduced
Negatively charged ions move to the positive electrode during electrolysis – they lose electrons and are oxidised
OILRIG – oxidation is loss, reduction is gain

6. Electrolysis

7. Electrolysis Products
Ionic substances in solution break down into elements during electrolysis – different elements are released depending on the particular ionic substance…

8. Negative Electrode
At the negative electrode, positively charged ions gain electrons – this is reduction (ions have been reduced)
Metal ions and hydrogen ions are positively charged – whether you get the metal or hydrogen during electrolysis depends on the position of the metal in the reactivity series: -
The metal will be produced if it is less reactive than hydrogen
Hydrogen will be produced if the metal is more reactive than hydrogen
E.g. the electrolysis of copper chloride solution produces copper at the negative electrode, but the electrolysis of sodium chloride solution produces hydrogen

9. Element Given Off At +ve Electrode
Positive Electrode
At the positive electrode, negatively charged ions lose electrons
This is oxidation – the ions have been oxidised
-ve Ion In Solution
Element Given Off At +ve Electrode
Chloride, Cl-
Chlorine, Cl2
Bromide, Br-
Bromine, Br2
Iodide, I-
Iodine, I2
Sulfate, SO4-2
Oxygen, O2

10. Anode & Cathode

11. Copper
Copper is a good conductor of electricity, and is used extensively to make electrical wiring and components
The extraction of copper from copper ore is done by reduction with carbon, however, the copper produced is not pure enough for use as a conductor, so it is purified using electrolysis

12. Copper Electrolysis
In this process, the positive electrode (anode) is made of the impure copper which is to be purified. The negative electrode (cathode) is a bar of pure copper. – the two electrodes are placed in a solution of copper(II) sulfate…
Copper ions leave the anode and are attracted to the cathode, where they are deposited as copper atoms – the pure copper cathode increases greatly in size, while the anode dwindles away (he impurities left behind at the anode form a sludge beneath it)

13. Copper Electrolysis
Copper purification via electrolysis…

14. Experiment
Complete the copper electrolysis experiment…

15. Aluminium
In the electrolysis of aluminium from its bauxite ore, cryolite it used to lower the temperature (cryolite is a less common ore of aluminium)
The electrodes are made of carbon

16. Half Equations
A half-equation shows you what happens at one of the electrodes during electrolysis – electrons are shown as e-
A half-equation is balanced by adding, or taking away, a number of electrons equal to the total number of charges on the ions in the equation…
At the negative electrode – positive ions gain electrons at the negative electrode, so are reduced: -
Cu2+ + 2e- → Cu
At the positive electrode – negative ions or neutral atoms lose electrons at the positive electrode and are oxidised: -
Cu → Cu2++ 2e-

17. Half Equations
A half-equation shows you what happens at one of the electrodes during electrolysis – electrons are shown as e-
A half-equation is balanced by adding, or taking away, a number of electrons equal to the total number of charges on the ions in the equation…
At the negative electrode – positive ions gain electrons at the negative electrode, so are reduced: -
Al3+ + 3e- → Al
At the positive electrode – negative ions or neutral atoms lose electrons at the positive electrode and are oxidised: -
2O2- → O2 + 4e-

18. Half Equations
A half-equation shows you what happens at one of the electrodes during electrolysis – electrons are shown as e-
A half-equation is balanced by adding, or taking away, a number of electrons equal to the total number of charges on the ions in the equation…
At the negative electrode – positive ions gain electrons at the negative electrode, so are reduced: -
2H+ + 2e- → H2
At the positive electrode – negative ions or neutral atoms lose electrons at the positive electrode and are oxidised: -
2Cl- → Cl2 + 2e-