Water does not easily remove grease from dirty hands because grease is nonpolar and water is polar; therefore they are immiscible. The addition of soap, however, results in the removal of the grease. Examine the following structure of soap and explain why soap works.
O
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CH3(CH2)16C ---- O- Na+
So what effect do you think that long chain in the soap has on grease?
Soap is a molecule that has both polar and nonpolar components, which allows it to effectively remove grease from dirty hands when combined with water. Let's examine the structure of soap to understand why it works.
The soap molecule consists of two main parts: a polar "head" and a nonpolar "tail." The polar head of the soap molecule contains an oxygen atom (O) and a sodium ion (Na+), which gives the head a slight negative charge. The nonpolar tail is a long chain of carbon (C) and hydrogen (H) atoms, represented as CH3(CH2)16C.
When soap is added to water, the polar head of the soap molecule is attracted to the polar water molecules due to their opposite charges. This process is called solvation or dissolving. The polar head of the soap molecule forms hydrogen bonds with water molecules, allowing it to easily dissolve in water.
Now, here's why soap works in removing grease: The nonpolar tail of the soap molecule is attracted to the nonpolar grease molecules on your hands. Grease is made up of nonpolar substances such as fats, oils, and lipids, which are not soluble in water alone. However, the nonpolar tail of the soap molecule can interact with the nonpolar grease molecules.
When you rub your hands together with soap and water, the soap molecules form structures called micelles. In a micelle, the nonpolar tails face inward, surrounding the grease particles in the center, while the polar heads face outward, interacting with water molecules. This arrangement allows the grease particles to become dispersed in water, forming tiny droplets called emulsions.
Once the grease is emulsified, it can be easily rinsed away with water because the emulsion of the nonpolar grease and soap molecules is now soluble in water. This is because the soap molecules act as a bridge between the water and the grease, allowing them to mix and be rinsed away.
In summary, soap works because its structure contains both polar and nonpolar components. The polar head of the soap molecule interacts with water while the nonpolar tail interacts with grease, enabling the emulsification and subsequent removal of grease from dirty hands when combined with water.