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

Answer:

At pH 8.59 the precipitation of acid will form.

Explanation:

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

pH = $pKa + log \frac{(S - S^{\circ})}{s^{\circ}}$

where S = total saturation solubility of the drug

S° = solubility of the undissociated species

substituting the respective values in equation, we get:

$pH = 6.48 + log \frac{( 4 \times 10^-2 - 3.07 \times 10^-4) }{3.07 \times 10^-7}$

pH = 8.59