1. How soap works: micelles

2. 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.

3. Application: Fats and oils don't dissolve in H2O.
Soap can suspend oil/dirt in such a way that it can be removed.

4. 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.

5. 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.

6. ie. Each soap molecule has a long hydrocarbon chain, sometimes called its 'tail', with a carboxylate 'head'.
a soap micelle 

7. 3-D diagram of a micelle . . .

8. “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.

9. Soap scum has given rise to special cleaners . . .
What’s the problem with these cleaners . . .

10. Cleaners are . . .
expensive;
they need to be applied;
they get washed down the drain.
So what’s the solution?

11. 1. Don’t wash.
2. Remove Ca2+ and Mg2+ ions from the water.
water softening unit
This is expensive and may not be possible.

12. 3. Make a different kind of soap.
But how?
What to change?

13. We can make a detergent (soap) where the “head” of the molecule a positive charge...
ie. a cationic synthetic detergent

14. 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.

16. Cationic Detergents good cleansing agents
possess germicidal properties
most cationic detergents are derivatives of ammonia.

17. cationic detergents (con’t)
often found in a shampoo
or clothes "rinse".
Able to neutralize the static electrical charges from residual anionic detergent molecules.

18. Also: Non-ionic syn. dets:

19. Non-ionic syn detergents
do not react with hard water ions;
used for dish washing liquid;
foam less than ionic detergents.

20. can form H-bonds with water also polar non-polar tail dissolves fats, and oils, etc

21. 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.

22. In what organ of the body is bile produced?

23. 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”.

25. 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 + glycerol
20 g 20 mL
6.0 mol/L

26. Test our hardened soap by adding it to:
tap water
deionized water
“hard” water
“soft” water
. . . results . . .

27. Observations In SOFT WATER good lather soap is in solution
In DE-IONIZED WATER
some lather
good solution of soap

28. Observations In 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

29. 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.