like dissolve like principle

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Presentation
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• like dissolve like principle
• When dissolving a solute, it involve
• a) Breaking the intermolecular force in the
  solvent
• b) Breaking the intermolecular force in the
  solute
• c) Formation the intermolecular force in the
  solution

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• If
• (enthalpy change of solution negative )
• Then the solute is soluble in solvent

solute-solute
attraction
solute-solvent
lt

attraction
solvent-solvent
attraction
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• Sugar is a covalent compound ,but what why it can
  be dissolved in water??
• in sugar, molecules are held together by weak
  Van der Waals force .
• when sugar dissolve in water,the energy release
  when sugar molecules form intermolecular force
  with water molecules is greater than or equal to
  the energy require to break the intermolecular
  force within sugar molecules and that of water
  molecules.

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• Therefore the energy released can be
  compensated for the energy required to break the
  solvent-solvent attraction and solute-solute
  attraction.

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• Ionic compound are usually soluble in water
• Now we use sodium chloride as an illustration
• When sodium chloride dissolve in water, the ions
  are solvated by the formation of many strong
  ion-dipole attraction.
• The energy release is greater or equal to that of
  the energy require to break the ionic bond within
  the compound and the hydrogen bond of water.

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Detergent

• A detergent molecule can be divided
• 1) metal ion part called hydrophilic
• 2)non polar part called hydrophobic

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Principle of detergent

• The hydrophobic part insert into grease and the
  hydrophilic part dissolve in water.
• Reason The hydrophilic part is a ionic head
  which form strong ion-dipole attraction with
  water molecule.
• When stirring, the grease become many small oil
  droplets which suspend through out the water.
• The grease therefore are removed.

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• Do NOT take the guiding principle too literally.
  It is only a guiding generalization to which one
  can find many exceptions.

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Exception

• Butanol is a polar molecule but do not dissolve
  in water which is polar solvent.
• Reason butanol can be consider into 2
  partnon-polar one and polar one.

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• The non-polar one form dipole-induced dipole
  interaction with water while the polar one form
  dipole-dipole interaction with water .
• However, since the non-polar one occupies major
  part of molecule, it outweight the strong
  attraction of polar part.
• Therefore the overall attraction between butanol
  molecule and water molecule is weak.

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END
BY Yun Lui Wong Ka Man