How does soap work?
Alan says:explain again how soap works
One of the main things soap does is to force water molecules to quit being so cliquish with each other.
You see, water molecules stick together something fierce. Much of their stickiness comes from the fact that each water molecule has an electric dipole. In other words, one end of the water molecule is positively charged and the other end is negative. The difference in charge is due to an unequal distribution of electrons in the molecule. You may have heard of this before if you ever heard water described as being a polar molecule.
Of course, as you know, water molecules don't keep completely to themselves; they do associate with certain other types of particles. Two examples are the ions in table salt and molecules of sugar.
However, dirt and grease aren't on water's "cool" list. Most dirt, oil and grease are made of molecules that do not possess significant electric dipoles. In other words, molecules in those substances are non-polar.
When water molecules come near these non-polar substances, they don't even consider unclustering. Perhaps you've seen water bead on a waxy surface? The reason it does that is because the water molecules stay crowded together as tightly as they can rather than interact with the waxy surface.
The net effect of all this is that, as you know, plain water doesn't do a very good job of cleaning grease and dirt off of things.
Enter soap.
Soap molecules have split personalities. On one end of a soap molecule, there is an electric dipole. Water molecules are very attracted to this end of the soap molecule. But, soap molecules also contain a long "tail" that has a structure much more similar to dirt or grease.
Once the soap molecules mix in with the water molecules, the long tails keep the water molecules from being able to crowd together so well. In technical terms, it is said that soap "reduces the surface tension" of water.
Since the water molecules cannot cluster together so tightly, they are more likely to slip into crevaces in the dirt or grime. Also, the long soap tails, not being so snobbish, can attract the grime via a much weaker, but still electrostatic, interaction called "London" or "van der Waals."
With the water and soap molecules now mixed in with the dirt, a little
agitation, such as rubbing your hands together, can loosen the dirt so that it can be rinsed away.
14 Comments:
Your the best science tacher in the world!
You suck at chemistry. Go back to school!
do you know this well? it seems youre just making randomness, to look like you actually know it but do not. you lack scientific terms
I know the subject of this particular post very well. I am trained as a physical chemist (PhD), so this is exactly the sort of thing I know.
When I am not as well trained in a subject area, I make sure to mention my limitations in my answer.
I write these posts for general audiences, so I avoid using technical terminology most of the time.
Thank You for sharing your knowledge.
thanks from putting it in simpler terms, everywhere else makes it way too complicated for the average person. good on ya.
THANK YOU.
It helped
I raid one article and i think i am going to get an A!
thank you for making it sound so simple and understandable! :)
okay how does soap KILL BACTERIA. does it have chemicals like triclosan that helps KILL IT?
you tell em girl!
You. are. awesome.
You just saved me and my lab report. THANKS.
For Johnny poopyhead who thought it wasn't scientific enough, try an wrap your brain around this one ... (ps, you did an awesome job simplifying it Miss science)
"Soap is an excellent cleanser because of its ability to act as an emulsifying agent. An emulsifier is capable of dispersing one liquid into another immiscible liquid. This means that while oil (which attracts dirt) doesn't naturally mix with water, soap can suspend oil/dirt in such a way that it can be removed.
The organic part of a natural soap is a negatively-charged, polar molecule. Its hydrophilic (water-loving) carboxylate group (-CO2) interacts with water molecules via ion-dipole interactions and hydrogen bonding. The hydrophobic (water-fearing) part of a soap molecule, its long, nonpolar hydrocarbon chain, does not interact with water molecules. The hydrocarbon chains are attracted to each other by dispersion forces and cluster together, forming structures called micelles. In these micelles, the carboxylate groups form a negatively-charged spherical surface, with the hydrocarbon chains inside the sphere. Because they are negatively charged, soap micelles repel each other and remain dispersed in water.
Grease and oil are nonpolar and insoluble in water. When soap and soiling oils are mixed, the nonpolar hydrocarbon portion of the micelles break up the nonpolar oil molecules. A different type of micelle then forms, with nonpolar soiling molecules in the center. Thus, grease and oil and the 'dirt' attached to them are caught inside the micelle and can be rinsed away.
Although soaps are excellent cleansers, they do have disadvantages. As salts of weak acids, they are converted by mineral acids into free fatty acids:
CH3(CH2)16CO2-Na+ + HCl → CH3(CH2)16CO2H + Na+ + Cl-
These fatty acids are less soluble than the sodium or potassium salts and form a precipitate or soap scum. Because of this, soaps are ineffective in acidic water. Also, soaps form insoluble salts in hard water, such as water containing magnesium, calcium, or iron.
2 CH3(CH2)16CO2-Na+ + Mg2+ → [CH3(CH2)16CO2-]2Mg2+ + 2 Na+
The insoluble salts form bathtub rings, leave films that reduce hair luster, and gray/roughen textiles after repeated washings. Synthetic detergents, however, may be soluble in both acidic and alkaline solutions and don't form insoluble precipitates in hard water. But that is a different story..."
Bet you're appreciating her answer right about now eh ? lol
I, of course, a newcomer to this blog, but the author does not agree
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