Question

Sulfadiazine is a sulfa drug. The solubility of Sulfadiazine is 3.07x10-4 mol dm-3 (as acid form). The pK a of the acid form is 6.48 Given a solution of sulfadiazine-sodium (salt) of 4x10-2 mole dm-3 concentration, calculate at what pH starts the precipitation of the acid form

Answer 1

At pH 8.59 the precipitation of acid will form.

Step-by-step explanation:

The pH below which the drug will begin to precipitate can be calculated using the relation

pH =
`pKa + log ((S - S^(\circ)))/(s^(\circ))`

where S = total saturation solubility of the drug

S° = solubility of the undissociated species

substituting the respective values in equation, we get:

`pH = 6.48 + log (( 4 * 10^-2 - 3.07 * 10^-4) )/(3.07 * 10^-7)`

pH = 8.59