Title: Electrolysis Complete the activities listed below 30/10/2019 Write a description of what you see happening in the animation. Use the keywords to help you. (Done? Sketch the diagram!) Keywords: Positive, negative, electrode, ion, electrolyte, gain, lose

Title: Electrolysis Complete the activities listed below 30/10/2019 The electrolyte contains positive and negative ions. Negative ions are attracted the positive electrode + lose electrons. Positive ions are attracted to the negative electrode + gain electrons

What is electrolysis? Electro: from the word “Electricity”. 30/10/2019 Electro: from the word “Electricity”. Lysis: from the Latin meaning “to split”/“to break”. Electrolysis is the decomposition (breaking up) of a molten or dissolved ionic compound by electricity passed through it (Direct Current, DC).

Why molten or dissolved? 30/10/2019 As solids, ionic compounds form a lattice structure. The ions (NOT ELECTRONS!!!) are held in place – cannot move. Electrolysis requires a flow of electrical charge. The ions (NOT ELECTRONS!!!) NEED to be able to move to carry charge! Molten (as liquid) the ions are free to move and carry charge. Dissolved, the ions are free to move and carry charge.

Uses for electrolysis 30/10/2019 Particular compounds require electrolysis to be extracted from their ore and purified. Metals that are more reactive than carbon (above carbon in the reactivity series) have to be extracted in this way as they cannot be displaced by carbon with heating. Electrolysis is very expensive: it uses lots of electrical energy.

Extracting copper from Copper Chloride 30/10/2019 Which ion is going to the negative electrode? Why? Which ion is going to the positive electrode? Why? What products are being formed?

Extracting copper from Copper Chloride 30/10/2019 Copper ions (Cu2+); positive ions attracted to negative electrode. Chloride ions (Cl-); negative ions attracted to positive electrode. Negative electrode: copper atoms; Positive electrode: chlorine gas.

Half-equations: At the anode 30/10/2019 2Cl-  Cl2 + 2e- Negative ions in the electrolyte lose electrons to the positive electrode. This is “oxidation” – loss of electrons. The negative ions lose their negative charge. A neutral element forms.

Half-equations: At the anode 30/10/2019 Cu2+ + 2e-  Cu Positive ions in the electrolyte gain electrons from the negative electrode. This is “reduction” – gain of electrons. The positive ions lose their positive charge. A neutral element forms.

Have a go at balancing these half equations 30/10/2019 Cu2+ + 2e-  Cu 2Cl-  Cl2 + 2e- Pb2+ + e-  Pb Br-  Br2 + 2e- H+ + e-  H2 Pb2+ + 2e-  Pb 2Br-  Br2 + 2e- 2H+ + 2e-  H2 Write half equations for the following ions: Na+ Al3+ O2- Na+ + e-  Na Al3+ + 3e-  Al 2O2-  O2 + 4e-

Combining/Balancing Half Equations 30/10/2019 Combining/Balancing Half Equations Na+ + e-  Na 2O2-  O2 + 4e- Al3+ + 3e-  Al Use the number of electrons to help balance the equations! Na+ + e-  Na vs. 2O2-  O2 + 4e- The number of electrons in each half equation must be equal! We need to multiple Na+ + e-  Na by 4! 4Na+ + 4e-  4Na Balance the half equations when combing: 2O2-  O2 + 4e- with Al3+ + 3e-  Al Lowest common factor for electrons = 12 3x (2O2-  O2 + 4e- ) = 6O2-  3O2 + 12e- 4x (Al3+ + 3e-  Al) = 4Al3+ + 12e-  4Al

Electrolysis in Aqueous Solutions 30/10/2019 If in a solution during electrolysis there are two elements that can be produced at an electrode then the less reactive one will be the one that is formed e.g. consider the negative electrode (cathode): Cu2+ ions and H+ ions: Cu forms Ca2+ ions and H+ ions: H2 forms Reactivity Series 1. Potassium 2. Sodium 3. Calcium 4. Magnesium 5. Aluminium 6. Zinc 7. Iron 8. Lead 9. Hydrogen 10. Copper 11. Mercury 12. Silver 13. Gold

Review 30/10/2019 Write a full explanation of what is happening in the animation below. Include: which ions go where, why they do this and both half equations.

Review 30/10/2019 The hydrogen ions are less reactive that the sodium ions. The positive hydrogen ions are attracted to the negative electrode. The hydrogen ions each gain one electron. 2H+ + 2e-  H2. This is called reduction. The negative chloride ions are attracted to the positive electrode. Each chloride ion loses one electron. 2Cl-  Cl2 + 2e- This is called oxidation.