The Two-Faced Detergent Whether soil particles are attached to carpet fibers, wood floors or restroom sinks, they need to be removed. But how is this done? Most of us wipe or scrub a dirty surface with soap and water without a second thought about how they actually work to remove soil. The process of removing dirt begins at the molecular level. In order to understand how soap works, we must first acknowledge what soap actually does. By definition, soap is a mixture of sodium or potassium salts and long chain organic acids.
One example of such a soap is Sodium stearate, NaCH 3 (CH 2) 16 CO 2. As you can see, a soap molecule is long. It has a carboxylate group called the head group which is polar and hydrophilic, or water attracting. The tail end is a fatty acid, which is non-polar and hydrophobic, or water repelling. In this way, soap is unique. One end attracts water while the other end pushes it away.
Initially soaps where made by heating sodium hydroxide with beef fat. Beef fat contains an ester formed between glycerol and stearic acid. The ester is then attacked by the sodium hydroxide, which releases the stearic acid as sodium stearate, How does all this help soap clean things? Well soap dissolves in water. There is nothing special about this, since many substances have this property. Water is polar; the H 2 O molecules have an attraction for other polar substances such as soap, which is polar on the oxygen end of the molecule. When soap is added to water its head group, which is hydrophilic, is attracted to the water.
The Essay on Synthetic Detergents Soap Water Made
... O-Na+This is an example of a soap molecule. The hydrocarbon end is non polar and hydrophilic (water hating) and the carboxylate end is ... this way work equally well in hard, soft, acid, hot or cold water. They don't leave scum and are very powerful ... -- salt of fatty acid (soap) + alcohol (glycerol). Caustic potash (potassium hydroxide) can be used instead of caustic soda (sodium hydroxide) but is more ...
Oil and grease etc. is non-polar, so only non-polar substances will dissolve in it. Therefore, oil and water do not mix. This is why Oil does not dissolve when you run water over it.
How does the oil wash off your hands if the water isn! |t soluble with the oil? This is where soap comes in. While soaps head is attracted to water its tail is attracted to non-polar substances such as oil. When oil and grease etc. mix with oil it creates a slightly polar substance because of the head group. This makes the oil soluble with water allowing you to wash off your hands with water and rinse the grease off.
Most detergents sold in stores today are more complicated then just a mixture of sodium or potassium salts and long chain organic acids. They usually have a surfactant, surface-active agent, instead of a regular soap. Surfactant Molecules are similar to the stearate ion. They have a hydrophilic head group and a hydrophobic tail and act almost the same as a regular soap molecule. The commercial detergents also have fillers, foam-reducing agents, and bleach. One disadvantage of soap is the scum they form in hard water.
This happens because of precipitation with with calcium stearate. The calcium forms because calcium salts are less soluble then sodium salts. Ca 2+ (HCO 3) 2 (aq) + Na 2 CO 3 (aq) “^3 Ca (C 17 H 35 CO 2) 2 (s) The scum may be avoided by precipitating the Ca 2+ ions from the water before the soap is added. Sodium Carbonate Ca (HCO 3) 2 (aq) (washing soda) will accomplish this task. Ca (HCO 3) 2 (aq) + Na 2 CO 3 (aq) “^3 CaCO 3 (s) + 2 NaH CO 3 (aq) The End.
