SolutionsHygiene and Cosmetics
1. Saponification
Which products are obtained when a triglyceride is heated with sodium hydroxide? Which of them is soap?
Glycerol (propane-1,2,3-triol) and the sodium salts of the three fatty acids. These salts (long-chain sodium carboxylates) are soap.
2. How soap cleans
Explain how soap removes a grease stain that water alone cannot remove.
The hydrocarbon tails of the soap molecules dissolve in the grease and the ionic heads face the water. Micelles form with the grease inside and a charged surface that disperses in the water and is washed away when rinsing.
3. Sunscreens
Which structural feature do organic sun filters share, and why is it necessary?
They have aromatic rings and conjugated double bonds. Conjugation lowers the energy needed to excite their electrons, so that they absorb the ultraviolet radiation (UVA or UVB) that would damage the skin.