Making of Soap – Saponificationts
- Alcohol react with carboxylic acid will form ester.
Ethanoic acid + ethanol → ethyl ethanoat (ester) + water
CH3COOH + C2H5OH → CH3COOC2H5 + H2O
This process is call esterification, and it is a condensation reaction (take out 1 water molecule and form a covalent bond).
- Inversely, the ester also can be decomposed to form alcohol and a salt by alkali such as sodium hydroxide.
ethyl ethanoat (ester) + sodium hydroxide → sodium ethanoat + ethanol
CH3COOC2H5 + NaOH → CH3COONa + C2H5OH
This process is a hydrolysis reaction (add 1 water molecule to the covalent bond and break the bond).
The Making of Soap
- As we learnt before, salt can be produced by the reaction between acid and alkali.
- Since soap is the sodium or potassium salt of fatty acid, we can produce soap by the reaction between fatty acid and alkali.
- Usually, the alkali that we use is sodium hydroxide (NaOH) or potassium hydroxide (KOH).
- Fat molecules are the molecules that form by a glycerol molecule and three fatty acid molecules.
- Since glycerol is an alcohol, while fatty acids are carboxylic acid, the process is call esterification, and it is a condensation reaction.
- Figure above shows that, we can separate the glycerol molecule from the fat molecule, and at the same time, produce three sodium salt of fatty acid.
- The hydrolysis of a fat or oil is given the particular name, saponification.
- The saponification reaction is the hydrolysis of fatty esters.
- The saponification reaction typically refers to the reaction that is carried out by a strong base.
- An example the saponification of tallow by sodium hydroxide. (tallow is the mixture of fats that are obtained by steam treating cow fat.)
- Summary of saponification reaction
- Normally some sodium chloride (NaCl) will be added into the solution to reduce the solubility of soap. As a result, we will obtain soap in solid form.