How soap works: micelles. Soap is an excellent cleanser non-polar CH 2 units; ionic COO - Na + group...
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Transcript of How soap works: micelles. Soap is an excellent cleanser non-polar CH 2 units; ionic COO - Na + group...
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How soap works: micelles
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• Soap is an excellent cleanser
non-polar CH2 units; ionic COO-Na+ group
• soap acts as an emulsifying agent
• it can disperse a liquid into another immiscible liquid.
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Application: Fats and oils don't dissolve in H2O.
• Soap can suspend oil/dirt in such a way that it can be removed.
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• Grease and oil are polar/non-polar and soluble/insoluble in HOH.
(non-polar, insoluble)
• When soap added to oil-containing solution, the nonpolar hydrocarbon portion of the soap breaks up the nonpolar oil molecules.
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• A micelle then forms—with nonpolar
solutes in the centre.
• The outside of the micelle is ionic—water soluble. Hence . . .
grease and oil washed away.
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ie. Each soap molecule has a long hydrocarbon chain, sometimes called its 'tail', with a carboxylate 'head'.
a soap micelle
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3-D diagram of a micelle . . .
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“Hard” Water Reduces Efficiency of Soap
• Hard water contains Ca2+ and Mg2+ ions
• These cations react with the anionic portion of soap to form an insoluble “scum” –aka calcium stearate.
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Soap scum has given rise to special cleaners . . .
What’s the problem with these cleaners . . .
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Cleaners are . . .
expensive;
they need to be applied;
they get washed down the drain.
So what’s the solution?
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1. Don’t wash.
2. Remove Ca2+ and Mg2+ ions from the water.
water softening unit
This is expensive and may not be possible.
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3. Make a different kind of soap.
But how?
What to change?
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We can make a detergent (soap) where the “head” of the molecule a positive charge...
ie. a cationic synthetic detergent
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Synthetic Detergents
• have similar molecular structures and properties as soap;
• less likely—or unlikely—to form soap “scum” with Ca2+ and Mg2+ ions (hard water);
• many have a negatively-charged “head”—they are anionic detergents.
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Cationic Detergents
• good cleansing agents
• possess germicidal properties
• most cationic detergents are derivatives of ammonia.
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cationic detergents (con’t)
• often found in a shampoo
or clothes "rinse".
• Able to neutralize the static electrical charges from residual anionic detergent molecules.
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Also: Non-ionic syn. dets:
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Non-ionic syn detergents
• do not react with hard water ions;
• used for dish washing liquid;
• foam less than ionic detergents.
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can form H-bonds with water
also polar
non-polar tail dissolves fats,
and oils, etc
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Biology Application: Bile Salts
• major action of a bile salt is to emulsify fats and oils into smaller droplets.
• enzymes can then break down the fats and oils.
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In what organ of the body is bile produced?
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Look at structure of a bile salt on next slide.
How do you think bile salts emulsify fats?
In the same way that soaps and detergents do . . .
with a polar “head” and non-polar “tail”.
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Lab: Preparation and Testing of Soap
General preparation of soap:
fat or oil + NaOH(aq) soap + glycerol
what we do:
coconut oil + NaOH(aq) soap + glycerol20 g 20 mL
6.0 mol/L
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Test our hardened soap by adding it to:
• tap water
• deionized water
• “hard” water
• “soft” water
. . . results . . .
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Observations
In SOFT WATER• good lather• soap is in solution
In DE-IONIZED WATER• some lather• good solution of soap
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ObservationsIn TAP WATER• virtually no lather• small pieces of soap
scum (ppt’ed soap) floating
In HARD WATER• no lather• no soap in solution• thick layer of soap
scum on top
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Conclusion:
Simple soap, such as the one that we made, works better in soft/hard water.
soft . . . why?
Soft water contains no Ca2+ or Mg2+ ions that can precipitate the soap.