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    Extraction of metals - Environmental aspects of metal extraction- Topic 7

    Environmental and economic advantages and disadvantages of recycling scrap metals compared with the extraction of metals.

    Right so here are the reasons as to how and why Iron + Aluminium are recycled.

    Advantages.

    - There is an environmental problem with build up of scrap
    - Scrap iron is needed for steel making
    - Extraction produces CO2which is a greenhouse gas.
    - It is less expensive to re-melt Al than to extract from ore

    Disadvantages.

    - Costs in collecting, sorting and transporting scrap may offset any savings through recycling.



    ~


    Advantage of using scrap iron to extract copper from aqueous solutions compared with the high temperature carbon reduction of copper oxide:

    Fe(s) + Cu2+(aq) -----------------> Cu(s) + Fe2+ (aq)


    - Low grade ores are used for this which might otherwise be waste.

    - It's a good use of scrap iron which is cheap.

    - The energy costs are low

    - And finally, there is much less CO2 produced in production.
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    Haloalkanes - Synthesis of chloroalkanes- Topic 8

    Okay so here is the chlorination of methane equation:

    CH4 + Cl2 -----------------------------> CH3Cl + HCl

    The product that is produced, which I've highlighted in yellow, is chloromethane.

    The mechanism name is called free radical substitution and the conditions that are required are UV light and excess CH4 to minimise further substitution.

    There are basically 3 STEPS to a free radical substitution reaction and they are:

    Initiation, propagation and termination.

    Propagation has two .. kinda sub-steps.

    Alright, so I'll show you how the mechanism works in this next post.
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    Haloalkanes - Synthesis of chloroalkanes- Topic 8


    CH4 + Cl2 -----------------------------> CH3Cl + HCl

    ~


    Step 1 - Initiation.

    Cl2 -------------------------------------------> Cl• + Cl•




    Step 2- Propagation.

    Cl• + CH4 -----------------------------------> HCl + •CH3

    •CH3 + Cl2 -----------------------------------> Cl• + CH3Cl




    Step 3 - Termination

    •CH3 + •CH3 -----------------------------------> CH3CH3/C2H6



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    Good luck for this exam! :jumphug: :hugs: :lovehug:
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    Haloalkanes - Synthesis of chloroalkanes- Topic 8

    Alright, so what I've done above is the basic one but here are further substitution products with excess chlorine + mechanisms.

    ~

    CH3Cl + Cl2 --------------> CH2Cl2 (dichloromethane) + HCl

    ~

    Step 1 - Initiation.

    Cl2 -------------------------------------------> Cl• + Cl•




    Step 2- Propagation.

    Cl• + CH3Cl ----------------------------------> HCl + •CH2Cl

    •CH2Cl + Cl2 -----------------------------------> Cl• + CH2Cl2




    Step 3 - Termination

    •CH2Cl + •CH2Cl -----------------------------------> CH2ClCH2Cl / C2H4Cl2




    ~


    CH2Cl2 + Cl2 --------------> CHCl3 (trichloromethane) + HCl


    ~


    Step 1 - Initiation.

    Cl2 -------------------------------------------> Cl• + Cl•




    Step 2- Propagation.

    Cl• + CH2Cl2 ----------------------------------> HCl + •CHCl2

    •CHCl2 + Cl2 -----------------------------------> Cl• + CHCl3



    Step 3 - Termination

    •CHCl2 + •CHCl2 -----------------------------------> CHCl2CHCl2 / C2H2Cl4



    ~

    For CCl4 (tetrachloromethane), you just repeat the above pattern.
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    Haloalkanes - Synthesis of chloroalkanes- Topic 8

    CFC's.

    Chloroalkanes + chlorofluoroalkanes can be used as solvents.

    For example, CFC's in aerosol propellants, refrigerants and anaesthetics.

    CFC's are relatively inert + therefore safe to use.


    ~

    CFC's and the ozone layer.

    So, the ozone formed naturally in the upper atmosphere is beneficial since it absorbs harmful UV radiation.

    The UV radiation in the upper atmosphere has enough energy to break C-Cl bonds in CFC's to produce Cl•

    The Ozone molecules readily reaction with the Cl•

    Here are the equations for the reactions that occur:

    Cl• + O3 ------------------> ClO• + O2

    ClO• + O3 ----------------> 2O2 +Cl•

    This therefore contributes to a hole in the ozone layer.


    As a result, there was a legislation to ban CFC's which was supported by chemists + alternative chlorine- free compounds have now been developed, E.g. HCFC's.
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    Haloalkanes - Nucleophillic substitution- Topic 8

    Nucleophile - Electron pair donor. E.g. :OH , :CN , :NH3


    Explanation for haloalkanes susceptibility to nucleophilic attack.

    - There is a polar C- X bond.

    - The electronegative X atom means that the C atom is electron deficient (𝛿+)

    - Therefore it is susceptible to attack by an electron pair donor.- Nucleophile.
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    Haloalkanes - Nucleophillic substitution- Topic 8

    Okay, so I'm going to be doing the 3 examples with 1-bromopropane.

    We'll start with NaOH.

    Reagent: NaOH

    Conditions: Warm, aqueous solution

    Equation: CH3CH2CH2Br + NaOH ----------> CH3CH2CH2OH (propan-1-ol) + NaBr

    Mechanism: I'll show this in the next post bc it's easier that way.- Just hoping it won't go onto the next page or anything like that bc otherwise it'll be annoying.
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    Mechanism for :OH with 1-bromopropane.

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    Now we'll move onto KCN.

    Reagent: KCN

    Conditions: Reflux KCN solution in ethanol

    Equation: CH3CH2CH2Br + KCN ----------> CH3CH2CH2CN (Butanenitrile)+ KBr

    Mechanism: The mechanism for :OHis identical to that of :CN but I'll do it anyway.(Again, in a separate post.)
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    Mechanism for :CN with 1-bromopropane.

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    Okay, finally it's NH3.

    Reagent: NH3

    Conditions: Heat excess NH3 in ethanol in sealed tube.

    Equation: CH3CH2CH2Br + 2NH3----------> CH3CH2CH2NH2 (1-propylamine OR 1-aminopropane)+ NH4Br

    Mechanism: As before etc etc.
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    Mechanism for :NH3 with 1-bromopropane.

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    Um, well this is just a tiny bit of additional info about the rate of hydrolysis .. so I'll just put it here:

    Okay so, the rate of hydrolysis of haloalkanes is influenced by the carbon–halogen bond enthalpy and is as follows:

    R- Cl < R- Br < R-I

    The reason for this is bc the bond strength decreases.
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    Haloalkanes - Elimination- Topic 8

    Concurrent substitution and elimination reactions of haloalkanes.

    So, you need to know that KOH can act both as a nucleophile and a base when it reacts with haloalkanes.

    ~

    As a nucleophile, the :OH- ion brings about a substitution reaction to form an ALCOHOL.

    As a base, the :OH- ion brings about the elimination of HBr to form an ALKENE.


    ~


    So to summarise:

    For a substitution:

    - The main organic product is an alcohol.

    - The role of the hydroxide ion is a Nucleophile

    - And the preferential conditions are warm, aqueous.


    ON THE OTHER HAND.

    For an elimination:

    - The main organic product is an alkene

    - The role of the hydroxide ion is a base (proton acceptor)

    - And the preferential conditions are hot, ethanolic.
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    Haloalkanes - Elimination- Topic 8

    Elimination reaction with 2-bromopropane

    CH3CHBrCH3 + KOH ----------------> CH3CH=CH2(Propene) + KBr + H2O

    ~

    Now I'll draw the elimination mechanism with this time, 1-bromopropane.. but on a separate post.

    Remember that the H atom lost must be on the adjacent C atom to the C - X bond.
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    Elimination mechanism with 1-bromopropane.

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    Alkenes- Structure, bonding + reactivity - Topic 9.

    Saturated hydrocarbon - Molecule containing single bonds only.

    Unsaturated hydrocarbon - Molecule containing at least one C=C bond

    Alkenes are therefore unsaturated hydrocarbons.

    ~

    Okay so:

    The nature of the C=C bond.

    - The arrangement around the >C=C< bond is planar.
    - The double bond is a centre of high electron density.

    ~

    Stereoisomerism. - Molecules with the same structural formula, but their bonds are arranged differently in space.

    E-Z isomerism

    - This is a type of stereoisomerism which is exhibited by alkenes.
    - They exist due to the restricted rotation about the C=C bond.
    - E-Z isomers have different physical properties but they contain the same functional group so they have similar chemical properties.
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    If a=/= b and c=/=d then E-Z isomers exist.

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    There are two E-Z isomers of but-2-ene.

    (just in case you can't read my handwriting..

    (z)- but-2-ene is on the left, (E)- but-2-ene is on the right.)

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