How do soaps work
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Transcript of How do soaps work
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How Does Soap Work?
“Like dissolves like”
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Polar Molecules • Some Molecules, such a H2O, 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.
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Non-Polar Molecules
• Other Molecules, such as hydrocarbons, or symmetrical molecules (O2, N2, CO2) are non -polar,meaning that their electrons are shared more or less equally and there is no positive end or negative end.
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“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)
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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.
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Long chain hydrocarbons • Long chain hydrocarbons such as
alkanes and alkenes are NON-POLAR Covalent molecules.
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Alkanes – non-polar
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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
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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
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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.
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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.
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Micelle
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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!
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Words you should understand
• Polar / polarity
• Non-polar
• Hydrophilic
• Hydrophobic
• Micelle
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