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Kenneth Kang

Monday, March 24, 1997


Soap Lab

Soap is formed when a gycerine tristerate changes into a gycerol and three sodium sterate esters. We were to create a similar soap with vegetable oil. The basic materials needed would be oil, NaOH, and heat. In the end, we made a small chunk of soap that actually worked.


In our study of hydrocarbons, we learned about esters. These molecules use a ROOR to join two chains of hydrocarbons. Soap utilizes this structure by allowing water to attach, via a hydrogen bond, to the oxygens while the hydrocarbon chain deals with the oily substance. The reaction we needed to perform involved gently heating a mixture of NaOH and oil together so that they could react.


Use 20 mL of oil in 80 mL of 50% ethanol/water solution with 10g of NaOH. We had to calculate the dillution required for the 95% alcohol solution to a 50% solution. The alcohol disolves the oil in the water which carries the NaOH ions. Heating this solution to around 100 °C allows it to react. Stirring is required to prevent abrupt boiling and splashing. The bubbles show a decrease in surface tension. After boiling, add 100mL of water and prepare 180mL saturated NaCl solution. Stir the mixture and allow it then to settle. Filtering the mixture will get you the soap which you can let dry.


Soap is definately a different color than the oil and the NaOH solution that we mixed it into. It thickened when it finally formed. It would be interesting to see if our soap really floats. Learning how to purify the soap could lead to further experiments in testing the composition of commercial soaps (test Ivory Soap's claim of 99.44% purity). The lab book suggested pH tests which could yield some additional information about its purity.