Chemistry 2.6 by Holly Jones https://padlet.com/hol_cjones/l3izufd3tc2m Made with an aura of mystery en-us 2019-01-30 12:12:16 UTC 2024-12-14 11:54:01 UTC hello@padlet.com https://padlet-assets.s3.amazonaws.com/icons/Soccerball.png Toxicity/ Environmental Effects hol_cjones https://padlet.com/hol_cjones/l3izufd3tc2m/wish/325795230 The use of halogenoalkannes is limited by statutory regulation bevause
  • Many of them are toxic eg. Polychloroalkanes
  • Others such as chlorofluorocarbons (CFCs) cause damage to Earth’s ozone (O3) layer.
Example
CCl2F2 —> Cl. + CClF2.   (Reaction 1 - Initiation)
Cl. + O3 —> ClO. + O2     (Reaction 2 - Propogation)
ClO. + O3 —> Cl. + 2O2   (Reaction 3 - Propogation)

In the upper atmosphere, CFCs encounter UV radiation, which ruptures the carbon-chloride bond to form a chloride radical. These radicals destroy ozone.
]]> 2019-01-30 12:12:28 UTC https://padlet.com/hol_cjones/l3izufd3tc2m/wish/325795230 Reflux of halogenoalkanes hol_cjones https://padlet.com/hol_cjones/l3izufd3tc2m/wish/325795232
  • Round bottom flask - Chemicals (NaOH (aq) and halogenoalkane) are being heated and are therefore evaporating.
  • Condenser- Evaporated chemicals are being condensed and move back down into the flask. They condensed due to the change in temperature caused by constant flow of water.
  • Effect on yeild - Yield will be increased as no chemicals are being lost through evaporation.
    • C4H9Br + OH- —> C4H9OH + Br-
    (1- Bromobutane) + (Hydroxide ion) —> (Butan-1-ol) + (Bromide ion)
    ]]>     2019-01-30 12:12:28 UTC https://padlet.com/hol_cjones/l3izufd3tc2m/wish/325795232     Uses of halogenoalkanes hol_cjones https://padlet.com/hol_cjones/l3izufd3tc2m/wish/325795233 1) Solvents - many RX molecules contain a polar C-X bond so can mix with a range of substances. It is non flammable and can therefore be used in dry cleaning
    2) Anaesthetics - many halogenoalkanes are general anaesthetics. Eg the gas halothane 
    3) Refrigerant- CFCs were used as refrigerants. The heat required to change the liquid to gas is removed from the fridge to cool it. ]]>     2019-01-30 12:12:28 UTC https://padlet.com/hol_cjones/l3izufd3tc2m/wish/325795233     Test for halogenoalkanes hol_cjones https://padlet.com/hol_cjones/l3izufd3tc2m/wish/325795234 Halogenoalkanes = RX (R= carbon chain) (X= Halogen)
    RX + NaOH(aq) —> ROH + Na+ + X-
    Halogenoalkane + Sodium Hydroxide —> Alcohol + Sodium ion + Halide

    Reagents: 1) Aqueous sodium hydroxide to break up RX
                       2) Dilute nitric acid then aqueous silver nitrate to see PPT 
    Observations: White PPT (chloride)
                              Cream PPT (bromide)
                              Yellow PPT (iodide) ]]>     2019-01-30 12:12:28 UTC https://padlet.com/hol_cjones/l3izufd3tc2m/wish/325795234     Substituting halogens hol_cjones https://padlet.com/hol_cjones/l3izufd3tc2m/wish/325795235 How easily we can substitute halogens (X) in halogenoalkanes depends on bond polarity and bond strength
    Bond polarity: C-F > C-Cl > C-Br > C-I
    The more polar the C-X bond, the easier it is to substitute X in the halogenoalkanes
    Bond lengths: C-I > C-Br > C-Cl > C-F
    Bond Strength: C-F > C-Cl > C-Br > C-I
    The weaker the bond, the easier it is to break the C-X bond and substitute X.]]>     2019-01-30 12:12:28 UTC https://padlet.com/hol_cjones/l3izufd3tc2m/wish/325795235     Elimination Reactions hol_cjones https://padlet.com/hol_cjones/l3izufd3tc2m/wish/325795236 2019-01-30 12:12:28 UTC https://padlet.com/hol_cjones/l3izufd3tc2m/wish/325795236 Mechanism 3: Nucleophilic Substitution hol_cjones https://padlet.com/hol_cjones/l3izufd3tc2m/wish/325795237 2019-01-30 12:12:28 UTC https://padlet.com/hol_cjones/l3izufd3tc2m/wish/325795237