emulsifiers, soap (1 Viewer)

[*Pooja*]

whats an emulsifier? i know an emulsion is a dispersion of small droplets of one liquid throughout another liquid.

identify the properties of soap that enable it to act as a surfactant.

descrtibe the molecular structure of a soap and use this to account for the cleaning action of soaps.

also for soaps and detergents and seeing the diff between them, is it the soap that has the functional group -COONa? I dont get how this is the functional group.

can sum1 pls explain this to me?

 

[mojako]

wel probably its best to read ur textbook and summary from the resources section or from here (http://www.boredofstudies.org/community/showthread.php?t=25844), or maybe the CSU site or other resources.
but, in short,
well you've answered what emulsion is urself...
it can be either oil-in-water (so the majority is water.. like in soap, milk, mayonnaise, cleansing cream), or water-in-oil (like in butter, margarine, lipsticks and moisturisers)
emulsions need surfactants to stabilise them.

surfactant is a substance which decreases the surface tension of water and hence solubilises dirt and grease.
soap.... is a surfactant becoz it has a long hydrocarbon tail which readily dissolves in oily substances, and an ionic head which easily disolves in water.
so the head goes with the water (hydrophilic) whilst the tail attaches to grease on clothes or on ur body etc and lift them up and make them dissolve in the water body.
those oily particles tend not to re-combine together and re-settle on the fabric becoz they're negatively charged and so repel one another.

molecular structure of soap.. basically the above.. the head is a negatively charged end (like COO-) whilst the tail is a looonng straight hydrocarbon chain.
if u want more depth read the textbook / summary ^^
(note: when I mentioned head and tail, they're both part of the thing apart from the Na+.. the Na+ basically means nothing.. I mean its not sumthing we're concerned about.. it separates from the other part when mixed with water)

yea ur sorta right about the diff between soap and deter.
deter can be anionic, non-ionic or cationic.
anionic, usually the head is a sulfonate, O-SO2-O- instead of COO-
non-ionic, the head is a few ethoxy group, (CH2-CH2-O)n, followed by a H at the end. if u draw it u can draw the head as O-O-O-O-OH
cationic, the head consists of N+ surrounded by 3 methyls on the right, top and bottom (the left connects to the tail which is a looong hydrocarbon chain)

previously, tha tail of detergents wasnt straight.. its branched.. but since branched ones take longer to biodegrate, now its straight as well.

 

[utopia_parkway]

i always thought that the sufactant properties of soap only removed the dirt.

it cleans of grease becuase of the non polar hydrocarbon tail and the polar carbonlate (or whatever it is) head which has nothing to do with the surface tension of the water.

is this true or do i just not understand soap.

 

[mojako]

whats the difference between dirt and grease?
I think its safe to assume they're the same thing

btw I dont think its carbonlate.. never heard of it...
in soap the head is COO-
probably its called carboxylate ion or something similar to that.

 

[mr EaZy]

he was referring to the surface tension of the water- not grease

 

[utopia_parkway]

whats the difference between dirt and grease?
I think its safe to assume they're the same thing

btw I dont think its carbonlate.. never heard of it...
in soap the head is COO-
probably its called carboxylate ion or something similar to that.

well the biggest differents is that dirt is dirt and grease is grease. other then that grease is made up from a collection of non-polar hydrocarbon chains and dirt is just like undisloved solids that get tangled up in your cloths when you roll around in the mad.