Final answer:
Soap is the thickener added to a liquid lubricant to make grease. Its molecular structure allows it to thicken grease effectively by bridging the gap between polar and non-polar substances.
Step-by-step explanation:
Grease is made by adding a thickener such as soap to a liquid lubricant. Soaps are effective thickeners in grease formulations due to their unique chemical structure, which includes both polar and non-polar ends. The hydrocarbon tail of the soap molecule is nonpolar and hydrophobic, enabling it to dissolve in oils, while the ionic head is polar and hydrophilic, allowing it to interact with water. This dual nature makes soap an exceptional intermediary that can bridge polar and non-polar substances. Moreover, soaps like sodium stearate are formed when animal fats are treated with a base such as sodium hydroxide, resulting in a saponification reaction that converts fatty acids into soap and glycerol. Soaps not only serve a cleansing role but also act as thickeners in the manufacturing of grease, improving its consistency and function as a lubricant.