C/WLO:• Define electrolysis• Recognise substances that can undergo

electrolysis• Predict the products of electrolysis

Electrolysis 04/02/14

Starter:1. Have your periodic tables out ready2. On your whiteboard write down any properties of ionic compounds that you rememberHINT: high or low boiling point? Conducts electricity? Soluble?

Is sodium chloride ionic or covalent?

• How do you know?• Metal + non-metal ionic compound

• Draw a sodium atom and a chlorine atom

• Show how they bond (HINT: you need an arrow)

• Draw the ions that are formed

ElectrolysisElectrolysis uses an electric current to break down an ionic substance into its elements

http://www.youtube.com/watch?v=TyNUqX5lb-0&safe=active

Predict the products of electrolysis of…

• Iron chloride• Lead iodide• Aluminium oxide• Zinc bromide• Copper chloride

We are going to carry out electrolysis of copper chloride?

• What will we make?• What will we see at the electrodes?• We are not going to do this with

molten copper chloride – can you think why not?

WEAR GOGGLES

1. Connect up the circuit as shown in the diagram (on the powerpack use 4V and DC)

2. Turn on the circuit and record your observations. You may smell chlorine at one electrode.

3. Use litmus paper to test the gas – chlorine turns litmus white4. As soon as you have made observations turn the power off –

CHLORINE IS TOXIC

Copper chloride solution (electrolyte)

Carbon electrodes

Power supply (4V)

Peer assess1. Bubbling / gas produced (1), colour change / chlorine smell (1)2. Red solid forming on electrode (1)3. Chlorine gas (1) turned litmus paper white (1)4. Copper (1)5. Positively charged copper ions move to negative electrode (1),

negatively charged chloride ions move to positive electrode (1)

6. Copper chloride has a high melting point (1) too high to melt in a school lab (1)

7. In molten or dissolved copper chloride the ions are free to move (1) but in a solid they cannot move (1)

8. Copper chloride copper + chlorine (1)9. CuCl2 (aq) Cu (s) + Cl2 (g) (1 for correct formulae, 1 for

correct state symbols)

C/WLO:1. Describe what happens to ions during electrolysis2. Predict products of electrolysis

Changes at electrodes

05/02/14

Starter:Ready for a quiz on last lesson’s work?

Molten NaCl - What happens at the electrodes?

• Cl- ion moves to positively charged electrode loses an electron to form a Cl atom – 2 Cl atoms bond to make a molecule of chlorine gas this is oxidation

• Na+ ion moves to negatively charged electrode gains an electron to form Na atom This is reduction

• OILRIG - Oxidation Is Loss (of electrons), Reduction Is Gain

For electrolysis of each molten compound, answer the following questions

• What forms at the positive electrode?• What forms at the negative electrode?• Describe what happens at each electrode. Use the words

ion, electron, oxidised, reduced, atom.

A – lithium fluorideB – lead bromide (careful – how many electrons are needed?)C – copper chloride

Ions: Li+ F- Pb2+ Br- Cu2+ Cl-

A - At the positive electrode fluoride ion loses an electron and forms fluorine atom. This is oxidation. 2 fluorine atoms bond together to form fluorine gas.At the negative electrode a lithium ion gains an electron and forms a lithium atom. This is reduction.

B – lead bromide (careful – how many electrons are needed?)At the positive electrode a bromide ion loses an electron

loses an electron and forms a bromine atom. This is oxidation. At the negative electrode a lead ions gains two electrons and forms a lead atom. This is reduction.C – copper chloride

At the positive electrode a chloride ion loses an electron and forms a chlorine atom. This is oxidation. At the negative electrode copper ions gain two electrons and form copper atoms. This is reduction.

Half equations

Eg Lead chloride

Pb2+ + 2e- Pb2Cl- Cl2 + 2e-

Write half equations for A, B and C

When electrolysis occurs in aqueous solutions, the changes at the electrode are more complex

• Water contains H+ and OH- ions

When electrolysis occurs in aqueous solutions, the changes at the electrode are more complex

• Water contains H+ and OH- ions• Sometimes H+ ions move to the negatively

charged electrode and form hydrogen H2 gas • Sometimes OH- ions move to the positively

charged electrode and form oxygen O2 gas

• RULE: the less reactive element will be produced

RULE: the less reactive element will be produced

Negative ion in solution

Element produced at positive electrode

chloride, Cl– chlorine, Cl2

bromide, Br– bromine, Br2

iodide, I– iodine, I2

sulfate, oxygen, O2

Predict what will be produced during electrolysis of:

1. Molten copper bromide2. Copper bromide solution3. Iron sulfate solution4. Potassium chloride solution5. Molten sodium chloride6. Solid calcium sulfate

Answer Qs in text book page 155