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R4 Extracting Aluminium

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					             Homework due
???




              Homework set
p50 Extracting aluminium, p54-55 Uses of metals,
  p48 Metal ores
AfL Task: How do you get the metals that I use
  every day?
Reactivity
                                               20 December
             Extracting Aluminium                     2011
Today’s learning objectives are to …
a) Describe and explain the extraction of aluminium
   from purified aluminium oxide by electrolysis
b) Explain how the methods of extraction of the metals
   are related to their positions in the reactivity series
c) Explain the uses of aluminium and iron, in terms of
   their properties.

Starter: BACK OF BOOKS
From last lesson:
Explain why you think carbon is more or less reactive
    than iron.
Reactivity
                                                                 The Reactivity Series
                                                                 Potassium
                                                                  Sodium
                                                                                     Iron Oxide can be
                                                                  Lithium
                                                                                     reduced by Carbon
                                                                                     because Iron is below C
                           Increasing difficulty of extraction

                                                                  Calcium
                                                                                     in the reactivity series.
                                                                 Magnesium
   Increasing reactivity




                                                                 Aluminium
                                                                                    Aluminium is above C,
                                                                    Zinc
                                                                                    so it cannot be
                                                                    Iron
                                                                             Carbon
                                                                                    extracted this way.
                                                                   Lead
                                                                  Copper
                                                                   Silver
                                                                   Gold
                                                                  Platinum
Reactivity
Extraction of metals and energy
changes
  The more vigorously an element forms
  compounds the harder it will be to get
  back that element from its compounds.

  For example, magnesium gives out lots of
  heat when it combines with oxygen.

  This means we will have to put lots of
  energy back to extract magnesium from
  magnesium oxide and so it will be hard to
  extract.
Reactivity
                  Extracting Gold
    Because gold occurs native (not combined with
    another element) its extraction is a low-tech affair
    that simply involves finding it!




Reactivity
             Potassium
              Lithium
              Sodium
                            Metals above carbon are
              Calcium
                            extracted by ELECTROLYSIS
             Magnesium
             Aluminium
              Carbon
                                 Metals below carbon are
               Zinc              extracted by heating them with
               Iron              carbon in a BLAST FURNACE
                Tin
               Lead
              Copper
               Silver    These unreactive metals can be found
               Gold      pure within rocks, not in a metal oxide
              Platinum
Reactivity
                   The big picture
  How do you get
             from this …………………. to this?




Reactivity
                  Aluminium Ore
       Aluminium ore is called Bauxite.

       Bauxite contains alumina (Al2O3 aluminium
       oxide) plus impurities such as iron oxide – it
       is purified before use.




Reactivity
                  Aluminium Ore
       Aluminium ore is called Bauxite.

       Bauxite contains alumina (Al2O3 aluminium
       oxide) plus impurities such as iron oxide – it
       is purified before use.

       To make aluminium the oxygen must be
       separated from the aluminium.

       What do we call this?

Reactivity
             More on Redox Reactions
     Oxidation and reduction can be explained in
     terms of gain or loss of oxygen.

     It can also be explained in terms of loss or
     gain of electrons.

     The words OIL RIG may help you remember
     which way round it goes.



Reactivity
      Oxidation is loss
      Reduction is gain

             OIL RIG
Reactivity
       Identify which species is being
         oxidised and which reduced
   iron + copper(II)      iron (II) + copper
   Fe(s) + Cu2+(aq)        Fe2+(aq) + Cu(s)



   Zinc + copper(II)      Zinc (II) + copper
   Zn(s) + Cu2+(aq)       Zn2+(aq) + Cu(s)




Reactivity
             Electrolysis of Aluminium

        At the cathode (+ve electrode):
        Al3+    +   3e-           Al

        At the anode (+ve electrode)

        2O2-             O2   +    4e-

Reactivity
               Key Words
Electrolysis   - the breakdown of a substance by
               electricity

Electrolyte    - compounds which don’t conduct
               electricity when solid but do conduct
               when molten or dissolved in water

Electrode      - carbon rods which carry electrons
               to and from the electrolyte

 Anode         - positively charged electrode

  Cathode
Reactivity
               - negatively charged electrode
                  Electrolysis
• Positively charged ions move
  to the negative electrode.
• Metal ions are positively-
  charged, so metals are
  produced at the negative
  electrode.

• Negatively-charged ions
  move to the positive
  electrode.
  Non-metal ions such as oxide
  ions and negatively-charged,
  so gases such as oxygen are
  produced at the positive
  electrode.
Reactivity
                   Electrolysis

Electrolysis is expensive - it requires a lot of
  energy…

    - ore must be molten (at a high melting point)

    - electricity is needed for the electrolysis
    process



Reactivity
                  Electrolysis
   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 is molten.

    Aluminium oxide has a very high melting point.
    Adding cryolite lowers the melting point and
    saves energy.




Reactivity
             Extraction of Aluminium




Reactivity
                Extraction of Aluminium
               CARBON ANODE




             THE CELL CONSISTS OF A   CARBON ANODE




Reactivity
                Extraction of Aluminium

              STEEL
             CATHODE
             CARBON
              LINING




             THE CELL CONSISTS OF A   CARBON LINED
                                      STEEL CATHODE



Reactivity
                Extraction of Aluminium



         MOLTEN
       ALUMINA and
        CRYOLITE




             ALUMINA IS DISSOLVED IN MOLTEN CRYOLITE Na3AlF6
             SAVES ENERGY - the mixture melts at a lower temperature


Reactivity
                Extraction of Aluminium



               MOLTEN
             ALUMINA and
              CRYOLITE



             ALUMINA IS DISSOLVED IN MOLTEN CRYOLITE Na3AlF6
                 aluminium and oxide ions are now free to move


Reactivity
             Extraction of Aluminium
         POSITIVE
     ALUMINIUM IONS
     ARE ATTRACTED
     TO THE NEGATIVE
         CATHODE



                                CARBON CATHODE



                     Al3+ + 3e-           Al
         EACH ION PICKS UP 3 ELECTRONS AND IS DISCHARGED


Reactivity
               Extraction of Aluminium

                                 CARBON ANODE
              NEGATIVE
             OXIDE IONS
                ARE
             ATTRACTED
               TO THE
              POSITIVE
               ANODE


                          O2-    O + 2e-
         EACH ION GIVES UP 2 ELECTRONS AND IS DISCHARGED


Reactivity
               Extraction of Aluminium
                                              ELECTRONS
                  OXIDATION (LOSS OF
               ELECTRONS) TAKES PLACE
                    AT THE ANODE
                                     CARBON ANODE

              REDUCTION
               (GAIN OF
             ELECTRONS)
             TAKES PLACE
                AT THE
                                         CARBON CATHODE
               CATHODE


             ANODE         3O2-            1½O2 + 6e-     OXIDATION


             CATHODE       2Al3+ + 6e-           2Al      REDUCTION


Reactivity
               Extraction of Aluminium
                                   CARBON DIOXIDE
             PROBLEM
             THE CARBON
                                   CARBON ANODE
               ANODES
             REACT WITH
             THE OXYGEN
             TO PRODUCE
               CARBON
               DIOXIDE




                 THE ANODES HAVE TO BE REPLACED AT
                REGULAR INTERVALS, THUS ADDING TO THE
                  COST OF THE EXTRACTION PROCESS

Reactivity
             Extraction of Aluminium




Reactivity
Your notes…
    • Label your diagram with temperatures and
      descriptions.
    • Copy out the equations for the reactions
      that take place.
    • Explain why cryolite is added.
    • Explain why electrolysis is expensive and
      the problem with using it to extract
      aluminium.



Reactivity
Uses of Al and Fe
1. Look at the pictures on p107 of Chemistry for
    you and read the text next to it.
    List the uses of Al and explain the reason for
    each one based on its properties.
2. Look at the table on p94, list the uses of steel
    explain why steel is used for them instead of
    Aluminium.




Reactivity
Consolidation
1. Complete Q1 and 4 on p99 of Chemistry for
   You in full sentences.
2. Complete Q18, 21, 22 on p139-140 of
   Chemistry for You in full sentences.




Reactivity
                The Reactivity Series

               copper               iron       magnesium


                aluminium          gold
                                              silver
     sodium             Can use carbon to extract


  Cannot use carbon to extract
                                       potassium

             carbon               lead              zinc
Reactivity
                      The Reactivity Series
     potassium
      sodium
      magnesium         Cannot use carbon to extract

        aluminium
          carbon
             zinc
              iron
             lead
                     Can use carbon to extract
          copper
           silver
Reactivity
           gold
              Quick questions
    1. Charged particles that move during
       electrolysis are called……
    2. How are each of the following metals
       extracted from their ores?
       a. potassium
       b. iron
       c. aluminium
       d. sodium
       e. lead
       f. calcium
Reactivity
        What do we use these metals
                for and why?


             Iron       Copper

         Aluminium
                           Steel
Reactivity
              Uses   Properties
       Iron

   Copper

 Aluminium

     Steel
Reactivity
                     Today’s…
…learning objectives were to …
a) Describe and explain the extraction of aluminium
   from purified aluminium oxide by electrolysis
b) Explain how the methods of extraction of the metals
   are related to their positions in the reactivity series
c) Explain the uses of aluminium and iron, in terms of
   their properties.

Self-assess your understanding of these learning
    objectives. 


Reactivity
Uses of Al and Fe
1. Look at the pictures on p141 of the Edexcel
    textbook and read the text near to them.
    List the uses of Al and explain the reason for
    each one based on its properties.
2. Read p143-4, list the uses of steel and explain
    the reason for each one based on its
    properties.
    Explain why steel is often used where
    Aluminium would work just as well.

Reactivity
              Consolidation
Complete Q2 on p146 and Q1 and 2 on p 147 of
  the Edexcel textbook in full sentences.

Extension
Complete Q1 from p146 and Q3 from p147.




Reactivity
             Answers p146




Reactivity
             Answers p147




Reactivity
             Answers p147




Reactivity

				
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