Glycerol is the second product of saponification, formed alongside soap when the ester bonds in an oil or fat are broken.
Glycerol is the second product of saponification, formed alongside soap when the ester bonds in an oil or fat are broken. Malay: gliserol · Chinese: 甘油.
Every oil or fat is a triglyceride, an ester of one glycerol molecule joined to three fatty acids. When hot concentrated alkali saponifies the fat, it splits off the three fatty acids as soap and leaves the glycerol backbone behind. Glycerol is a colourless, sweet-tasting, syrupy alcohol with three –OH groups, which is why it mixes freely with water and dissolves in the water layer during soap-making. It is not a waste product: it is recovered and sold for use in medicines, cosmetics, toothpaste and food, where it acts as a moisturiser, softener and sweetener. Being able to hold water is what makes glycerol so useful in skin creams.
Example. When palm oil is boiled with sodium hydroxide, the soap floats out after salt is added, and the glycerol stays dissolved in the liquid below. Factories recover this glycerol by distilling off the water, so both products of the one reaction are put to use and nothing is wasted.
Confusion to avoid. Do not forget glycerol when you write the products of saponification. Many students name only the soap and lose the second mark. Also keep glycerol, which is the alcohol, separate from the fatty acids, which are the carboxylic acids; the fat is the ester joining the two, and saponification simply pulls them apart again into an alcohol and a set of salts.
Naming glycerol as the second product is a small but frequently tested point in this chapter, and it links soap-making back to the ester structure of oils and fats. Getting both products right is a routine SPM Chemistry requirement.
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