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Reactions of sodium ricinoleate
Sodium ricinoleate was made in this reaction by the hydrolysis of the lipid present in castor oil:
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C3H5(OC18H33O2)3 + 3NaOH ⇒ C3H5(OH)3 + 3C18H33O3Na |
It is easier to represent the fatty acid residue by the symbol Ric:
|
CH2RicCHRicCH2Ric + 3NaOH ⇒ CH2OHCHOHCH2OH + 3NaRic |
In the first reaction of the sodium ricinoleate we react the solution with a solution of calcium ions. This illustrates the use of soap in hard water areas. Hard water contains calcium and/or magnesium ions in solution, obtained when natural waters flow over rocks containing these ions. When soap is used with hard water the insoluble calcium salt is formed, and this appears as a white scum. This is rather unattractive, and increases the amount of soap needed to form a lather. In the video we see the formation of a precipitate of calcium ricinoleate:
|
2NaRic(aq) + Ca2+(aq) ⇒ Ca(Ric)2(s) + 2Na+(aq) |
When a strong acid, like hydrochloric acid, is added to the salt of a weak acid, the weak acid is formed. This is because there is a relatively strong attraction between the weak acid anions and the hydrogen ions from the strong acid. In this case, when we add hydrochloric acid to the sodium ricinoleate solution, ricinoleic acid is formed. This is a carboxylic acid with a long non-polar carbon chain. It is, therefore, sparingly soluble in water and appears as a white precipitate:
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NaRic(aq) + H+(aq) ⇒HRic(s) + Na+(aq) |