A tribasic (or triprotic) acid is an acid that has three hydrogen ions to donate in an acid-base reaction. With the help of the figure we can see how citric acid is an example of tribasic acid, as it has three COOH carboxyl groups that can easily transfer hydrogen H.
Magnesium citrate exists in both a 1: 1 proportion (1 magnesium molecule per citrate molecule), and in a 3: 2 proportion (3 magnesium molecules per 2 molecules of citrate).
1: 1 magnesium citrate is called dibasic because it is a dibasic salt of citric acid; in fact it has 2 univalent basic groups (COO-) per molecule, derived from the 2 carboxylic groups that have given up their hydrogen during the reaction.
3: 2 magnesium, on the other hand, is called tribasic because it has 3 univalent basic groups (COO-) per molecule, derived from the 3 carboxylic groups that gave up their hydrogen during the reaction.
Tribasic magnesium citrate is clearly richer in magnesium (+ 42.6% by weight) than dibasic magnesium citrate; moreover, it is more alkalizing, since it can accept three hydrogen ions H + against the two accepted by the dibasic. However it is less soluble in water.
