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1、ELECTROLYSIS Module C2,Splitting up ionic compounds (F),Molten compounds,Ionic solutions & discharge rules,Q = It and OILRIG,Brine and purifying copper,Cl- ION,Na+ ION,SPLITTING UP IONIC COMPOUNDS 1,Ionic compounds (eg sodium chloride) are made from: POSTIVE IONS (atoms which LOST negative electrons
2、) NEGATIVE IONS (atoms which GAINED negative electrons) As these ions have OPPOSITE CHARGES they attract each other strongly to form IONIC BONDS,SPLITTING UP IONIC COMPOUNDS 2,2 ways to split up the ions:,800C,20C,SEPARATING THE IONS 1,+,_,Battery pulls electrons off one electrode and pushes them on
3、to the other,Metal ELECTRODE,ELECTRON,This IS SHORT OF electrons so becomes POSITIVELY CHARGED “ANODE”,This HAS EXTRA electrons so becomes NEGATIVELY CHARGED “CATHODE”,+,MOLTEN IONIC COMPOUND,+ ANODE,- CATHODE,When the battery is switched on, the + IONS move to the CATHODE the IONS move to the + ANO
4、DE,SEPARATING THE IONS 2,This gives a way to SPLIT UP IONIC COMPOUNDS: “ELECTROLYSIS”,Example 1: Splitting up MOLTEN SODIUM CHLORIDE (salt),+,Cl-,Cl-,Cl-,Cl-,- chloride IONS lose their extra electrons and turn into neutral chlorine ATOMS,Both together: 2Cl- 2e- + Cl2,Example 1: Splitting up MOLTEN S
5、ODIUM CHLORIDE (salt),+,+ sodium IONS gain an extra electron and turn into neutral sodium ATOMS,molten sodium metal sinks to bottom,Example 1: Splitting up MOLTEN SODIUM CHLORIDE (salt),MOLTEN SODIUM CHLORIDE,+ ANODE,- CATHODE,CHLORINE gas Cl2,SODIUM metal Na,ELECTRONS,Example 2: Splitting up MOLTEN
6、 LEAD BROMIDE PbBr2,MOLTEN LEAD BROMIDE,+ ANODE,- CATHODE,BROMINE gas Br2,LEAD Metal Pb,ELECTRONS,Both together: 2Br- 2e- + Br2,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 solu
7、tion (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),IONIC SOLUTION,Which ions gain or lose electrons (“get discharged”) and which stay in solution?,IONIC SOLUTIONS: At the CATHOD
8、E,+,sodium ION, missing 1 electron,Hydrogen ATOM, NEUTRAL,hydrogen ION, missing 1 electron,As HYDROGEN is LESS REACTIVE than SODIUM, it is discharged. The sodium ions stay in solution.,which ions?,+,Cl-,Cl-,Cl-,Cl-,chloride ION, extra 1 electron,chlorine ATOM, NEUTRAL,IONIC SOLUTIONS: At the CATHODE
9、 halogen compounds,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,O,O,O,O,O,hydroxide ION, from water extra electron,which ions?,+,nitrate ION, extra 1 electron,NO3-,Oxygen atom,IONIC SOLUTIONS: CATHODE non halogen compo
10、unds,O,hydroxide ION, OH- from water, extra electron,O,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.,which ions?,+ ANODE Attracts ions (Anions),If ions are HALOGENS ie chlori
11、de Cl- bromide Br- iodide I- the HALOGEN is produced.,If ions are NOT HALOGENS Eg sulphate SO42-, nitrate NO3- carbonate CO32- OXYGEN is produced.,- CATHODE Attracts + ions (Cations),If + ions (metals) are MORE REACTIVE than hydrogen K, Na, Ca, Mg, Zn, Fe Then HYDROGEN is produced,If + ions (metals)
12、 are LESS REACTIVE than hydrogen Cu, Ag, Au Then the METAL is produced,RULES FOR IONIC SOLUTIONS,potassium chloride,Compound,State,Anode (+),Cathode (-),Ions,molten,K+ Cl-,potassium,chlorine,aluminium oxide,molten,Al3+ O2-,aluminium,oxygen,copper chloride,solution,Cu2+ Cl- H+ OH-,copper,chlorine,sod
13、ium bromide,solution,Na+ Br- H+ OH-,hydrogen,bromine,silver nitrate,solution,Ag+ NO3- H+ OH-,silver,oxygen,potassium chloride,solution,K+ Cl- H+ OH-,hydrogen,chlorine,zinc sulphate,solution,Zn+ SO42- H+ OH-,hydrogen,oxygen,(REACTIVITY: K+ Na+ Ca2+ Mg2+ Al3+ Zn2+ Fe3+ H+ Cu2+ Ag+ Au3+ ),(REACTIVITY:
14、K+ Na+ Ca2+ Mg2+ Al3+ Zn2+ Fe3+ H+ Cu2+ Ag+ Au3+ ),ELECTROLYSIS makes a CIRCUIT,Complete electric circuit: Current carried by: ELECTRONS in electrodes/wires IONS in the electrolyte,To DOUBLE the MASS of substance discharged at electrodes: 2 x CURRENT (2x batt. voltage) 2 x TIME current flows for (Q
15、= I t),Cl-,Cl-,Cl-,Cl-,OILRIG,ions LOSING electrons to become atoms is called OXIDATION (even though oxygen may not be involved),+ ions GAINING electrons to become atoms is called REDUCTION,Oxidation is loss, reduction is gain OILRIG,INDUSTRIAL USES OF ELECTROLYSIS,To extract reactive metals such as
16、 ALUMINIUM, sodium, magnesium etc from their compounds. This is EXPENSIVE due to the large amounts of electrical energy needed. Aluminium is extracted from bauxite (Al2O3). 2. Electrolysis of BRINE (salt solution) to produce CHLORINE (for disinfectants and plastics) HYDROGEN (for ammonia fertilisers
17、, margarine) SODIUM HYDROXIDE (for soap and cleaning agents) 3. Purifying copper. The copper for wiring etc needs to be more pure than that produced in a blast furnace. Electrolysis is used to convert impure copper to pure copper,see below,see below,INDUSTRIAL ELECTROLYSIS OF BRINE,ANODE OH- and Cl-
18、,2Cl- 2e- + Cl2,OH- left in solution so concentration grows,CATHODE H+ and Na+,2H+ + 2e- H2,Na+ left in solution so concentration grows,Chlorine gas,Hydrogen gas,Sodium chloride solution (neutral) slowly changed to sodium hydroxide solution (alkaline),BRINE (NaCl solution),Industrial chlorine produc
19、tion from electrolysis of brine,PURIFYING COPPER,Copper atoms from impure copper are OXIDISED to copper ions,Copper ions transported from anode to cathode,Copper ions from impure copper are REDUCED to copper atoms,As the atoms of the impurities are not transported, the copper that builds up on the anode is extremely pure.,Over time, the impure anode dissolves away and the impurities sink to the bottom. The pure cathode grows as more pure copper is deposited on it. Why will the concentration of the solution stay the same?,