How do soaps work

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  • 1. How Does Soap Work? “ Like dissolves like”
  • 2. Polar Molecules
    • Some Molecules, such a H 2 O, are POLAR -meaning that they have a (slightly) positive end and a (slightly) negative end like a battery.
    • Polarity is the result of unequal sharing of electrons in a bond causing one atom in the bond to be more negative than the other.
  • 3. Non-Polar Molecules
    • Other Molecules, such as hydrocarbons, or symmetrical molecules (O 2 , N 2 , CO 2 ) are non -polar,meaning that their electrons are shared more or less equally and there is no positive end or negative end.
  • 4. “ Like dissolves Like”
    • Polar things interact with Polar things, and repel non polar things
      • Ex: Water (polar) will dissolve salt (ionic), but will not mix with oil (non polar).
    • Non Polar things interact with non Polar things and repel Polar things
      • Ex: Kerosene (non polar) will mix with oil (non polar) but not water (polar)
  • 5. Hydrophilic and Hydrophobic
    • “ Hydro” – water
      • “ phobic” – doesn’t like! (non-polar)
      • “ philic” – does like (polar)
    • Things that interact with polar water molecules are water-loving or hydrophilic. Hydrophilic substances include Salts, alcohols, and anything with polarity.
    • Things that don’t like water are water-hating or hydrophobic . Hydrophobic substances are oils, grease, and anything Non polar.
  • 6. Long chain hydrocarbons
    • Long chain hydrocarbons such as alkanes and alkenes are NON-POLAR Covalent molecules.
  • 7. Alkanes – non-polar
  • 8. Alkanes with stuff added on…
    • Adding functional groups such as alcohol (-OH) or Carboxyl (COOH), causes one part of the molecule to become Polar
      • The rest of the molecule is still non-polar, especially if it’s a really long chain
  • 9. Saponification reaction
    • Soap is made by reacting a fatty acid with a base
    • This breaks the Carboxyl bonds to form a soap (with a polar end) and Glycerol
  • 10. Soaps
    • A soap molecule has a Polar hydrophilic ‘head’ and a Non polar hydrophobic ‘tail’
    • The head will interact with the polar water molecules and the tail will interact with the grease molecules.
    • This means a soap can interact with both oil and water.
  • 11. Soaps
    • In this way, the soap molecules can cause grease molecules to dissolve into the water, by forming micelles which allow small particles of grease to be lifted up into the water.
  • 12. Micelle
  • 13.  
  • 14. Soap dissolves grease
    • The non-polar part of soap dissolves the grease,
    • The other end dissolves salts, polar stuff and associates with water
    • Voila! Clean dishes!
  • 15. Words you should understand
    • Polar / polarity
    • Non-polar
    • Hydrophilic
    • Hydrophobic
    • Micelle
  • 16.