Ampholytes are compounds that can function either as an acid or as a base. Examples on ampholytes include water, H2PO4-, HPO4-2, and amino acids. Assume that an ampholyte (HA-) dissolves in water. It can either produce a proton along with (A-2) or it can gain a proton to produce (H2A). The equation that can be used to calculate the pH of such a solution is the following:
Where, K1 and K2 are the first and second ionization constant of the acid (H2A), Kw is the ionization constant of water, and C is the concentration of the ampholyte (HA-) dissolved in solution in moles/ liter (M). For example, if we have a solution containing 0.005 M of monobasic sodium ascorbate (NaHA) and ascorbic acid has ionization constants K1 = 5.0 × 10-5, and K2 = 1.6 × 10-12 then by applying the above equation we get pH = 7.88 (at 25 °C).
Where, K1 and K2 are the first and second ionization constant of the acid (H2A), Kw is the ionization constant of water, and C is the concentration of the ampholyte (HA-) dissolved in solution in moles/ liter (M). For example, if we have a solution containing 0.005 M of monobasic sodium ascorbate (NaHA) and ascorbic acid has ionization constants K1 = 5.0 × 10-5, and K2 = 1.6 × 10-12 then by applying the above equation we get pH = 7.88 (at 25 °C).
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