C3.4 – Electrolysis and cells Learning Objectives: To describe the properties of metals To explain the processes involved in electrolysis To describe the principle behind a dry cell

Name all the properties of metals that you can

catalysts density ductile heat high properties transition Iron and copper are both __________ metals. They have __________ melting points, they are good conductors of __________ and electricity and they have a high __________. Transition metals have uses linked to their __________. For example, copper is __________ and so is used to make wires. Some transition metals are used as __________ , speeding up chemical reactions.

SPLITTING UP IONIC COMPOUNDS 1 Cl- ION Na+ ION Ionic compounds (eg sodium chloride) are made from: POSTIVE IONS (atoms which LOST negative electrons) NEGATIVE IONS (atoms which GAINED negative electrons) As these ions have OPPOSITE CHARGES they attract each other strongly to form IONIC BONDS

- - MELT - DISSOLVE 800°C 20°C SPLITTING UP IONIC COMPOUNDS To make ions move: - + + - MELT + - DISSOLVE H2O 800°C 20°C

_ + SEPARATING THE IONS 1 Metal ELECTRODE ELECTRON Battery pulls electrons off one electrode and pushes them onto the other This IS SHORT OF electrons so becomes POSITIVELY CHARGED “ANODE” This HAS EXTRA electrons so becomes NEGATIVELY CHARGED “CATHODE”

Define the terms: Electrolyte Electrode Anode Cathode Inert

Electrolysis Practical Select one of the test substances and connect it into the circuit. Switch on the power supply. Does the bulb light? Look carefully for any signs of reaction. These might include: gases being given off changes taking place on the surface of the electrodes changes taking place in the liquid.

+ - - - - - - - SEPARATING THE IONS 2 MOLTEN IONIC COMPOUND + + + + + + ANODE - CATHODE When the battery is switched on, the + IONS move to the – CATHODE the – IONS move to the + ANODE This gives a way to SPLIT UP IONIC COMPOUNDS: “ELECTROLYSIS”

+ - At ANODE: Cl- e- + Cl 2Cl- → 2e- + Cl2 then: Cl + Cl Cl2 (gas) Example 1: Splitting up MOLTEN SODIUM CHLORIDE (salt) - = chloride ION, extra 1 electron Cl- Cl chlorine ATOM, NEUTRAL Cl2 molecule + - chloride IONS lose their extra electrons and turn into neutral chlorine ATOMS Cl Cl Cl- Cl- Cl Cl Cl- Cl- At ANODE: Cl- e- + Cl Both together: 2Cl- → 2e- + Cl2 then: Cl + Cl Cl2 (gas)

molten sodium metal sinks to bottom Example 1: Splitting up MOLTEN SODIUM CHLORIDE (salt) = sodium ION, missing1 electron sodium ATOM, NEUTRAL Na+ + Na + + sodium IONS gain an extra electron and turn into neutral sodium ATOMS Na Na+ Na Na+ Na Na+ Na+ Na At CATHODE: Na+ + e- Na molten sodium metal sinks to bottom

MOLTEN SODIUM CHLORIDE Example 1: Splitting up MOLTEN SODIUM CHLORIDE (salt) - CATHODE + ANODE ELECTRONS SODIUM metal Na CHLORINE gas Cl2 MOLTEN SODIUM CHLORIDE Na+ Cl- At ANODE: Cl- e- + Cl At CATHODE: Na+ + e- Na Cl + Cl Cl2 (gas)

Br- e- + Br Pb2+ + 2e- Pb At ANODE: At CATHODE: Br + Br Br2 (gas) Example 2: Splitting up MOLTEN LEAD BROMIDE PbBr2 - CATHODE + ANODE ELECTRONS LEAD Metal Pb BROMINE gas Br2 MOLTEN LEAD BROMIDE Pb2+ Br- At ANODE: Br- e- + Br At CATHODE: Pb2+ + 2e- Pb Br + Br Br2 (gas) Both together: 2Br- → 2e- + Br2

SODIUM CHLORIDE SOLUTION NaCl (aq) What happens when the ionic compounds are dissolved in water? Here, water molecules break up into HYDROGEN IONS, H+ and HYDROXIDE IONS OH- H2O  H+ + OH- So, in an ionic solution (eg sodium chloride solution), there will be FOUR types of ion present: TWO from the ionic compound and TWO from the water (H+ + OH-) SODIUM CHLORIDE SOLUTION NaCl (aq) H+ OH- Cl- Na+ H+ Na+ Na+ H+ OH- Cl- Cl- OH-

IONIC SOLUTION H+ OH- H+ OH- Cl- Na+ H+ Na+ Na+ OH- Cl- Cl- Which ions gain or lose electrons (“get discharged”) and which stay in solution?

+ At CATHODE: 2H+ + 2e- H2 IONIC SOLUTIONS: At the CATHODE which ions? sodium ION, missing 1 electron hydrogen ION, missing 1 electron Na+ H+ H Hydrogen ATOM, NEUTRAL which ions? + As HYDROGEN is LESS REACTIVE than SODIUM, it is discharged. The sodium ions stay in solution. Na+ H H+ Na+ H H+ At CATHODE: 2H+ + 2e- H2

IONIC SOLUTIONS: At the CATHODE – halogen compounds hydroxide ION, from water extra electron chloride ION, extra 1 electron Cl- chlorine ATOM, NEUTRAL O H Cl + If the – ion is a HALOGEN (Cl, Br, I) it is discharged and chlorine (or Br or I) is given off and the OH - ions stay in solution H O O H Cl Cl Cl- Cl- H O O H Cl Cl Cl- Cl- which ions? At ANODE: 2Cl- 2e- + Cl2

+ At CATHODE: 4OH- 2H2O + O2 + 4e- IONIC SOLUTIONS: CATHODE – non halogen compounds hydroxide ION, OH- from water, extra electron Oxygen atom nitrate ION, extra 1 electron O NO3- O H + NO3- NO3- If the – ion is NOT a halogen (eg nitrate, sulphate etc) then the HYDROXIDE ions from the water are discharged to make WATER and OXYGEN gas. The other ions stay in solution. O H O H NO3- NO3- O H O H which ions? At CATHODE: 4OH- 2H2O + O2 + 4e-

RULES FOR IONIC SOLUTIONS + ANODE Attracts – ions (‘Anions’) - CATHODE Attracts + ions (‘Cations’) If – ions are HALOGENS ie chloride Cl- bromide Br- iodide I- the HALOGEN is produced. If + ions (metals) are MORE REACTIVE than hydrogen K, Na, Ca, Mg, Zn, Fe Then HYDROGEN is produced If – ions are NOT HALOGENS Eg sulphate SO42-, nitrate NO3- carbonate CO32- OXYGEN is produced. If + ions (metals) are LESS REACTIVE than hydrogen Cu, Ag, Au Then the METAL is produced

Zinc atoms turn into ions, and electrons travel around the circuit. When they reach the metals cap they travel down the positive pole. The manganese dioxide absorbs the electrons. There is an electrolyte (ammonium chloride in this case) which is kept damp and which the ions can travel through.

Recipe Time Write a recipe of the lesson (or of your learning)