= Saponification of triglycerides
A <triglyceride> contains three <ester> linkages joining <glycerol> to <fatty acid>-derived <acyl groups>. Complete <saponification> therefore consumes three <hydroxide> equivalents per <triglyceride>, yielding one <glycerol> and three <fatty acid> <carboxylates>.<Organic Chemistry by John McMurry/27.2 Soap>[Organic Chemistry by John McMurry; §27.2, opening chemical definition and fat hydrolysis equation]{ref}
Writing the three <hydrocarbon> groups separately allows their compositions to differ:
$$
\begin{aligned}
&\mathrm{C_3H_5[OC(=O)R_1][OC(=O)R_2][OC(=O)R_3]}+3\mathrm{OH^-}\\
&\qquad\longrightarrow\mathrm{C_3H_5(OH)_3}
+\mathrm{R_1COO^-}+\mathrm{R_2COO^-}+\mathrm{R_3COO^-}.
\end{aligned}
$$
This is the preceding <ester> <chemical equation> applied three times: each linkage supplies one <carboxylate>, and each formerly esterified <oxygen> on the <glycerol> scaffold gains one <hydrogen>. The two sides retain the same three $\mathrm R_i$ groups and have net <electric charge> $-3$.
<Soap> consists of <sodium> or <potassium> salts of long-chain <fatty acids>. Its <carboxylate> head is <hydrophilic>, while its long <hydrocarbon> tail is <hydrophobic>. This makes it an <amphiphile> and a <surfactant>: the tails can associate with grease while the heads remain exposed to <water>, helping disperse grease for rinsing. An <acetate ion> is also a <carboxylate>, but lacks the long <hydrophobic> tail that gives <soap> this cleaning role.<Organic Chemistry by John McMurry/27.2 Soap>[Organic Chemistry by John McMurry; §27.2, chemical definition and paragraphs on the ionic head, hydrocarbon tail and removal of grease]{ref}
\Image[/soap-head-tail-grease-water.png]
{title=Soap links a hydrophobic grease region to surrounding water}
{description=Original schematic cross-section of a <soap>-coated grease droplet in <water>. Circles denote <hydrophilic> <carboxylate> heads; orange lines denote <hydrophobic> <hydrocarbon> tails. The layout explains <amphiphile> orientation rather than depicting measured dimensions or individual <chemical bonds>.}
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