APhA NAPLEX Review Questions WITH COMPLETE SOLUTIONS

If the pka of a weak acid is 2.5, at which pH will this drug become more ionized? A. pH 5 B. pH 2.5 C. pH 1.5 D. pH 1 correct answer: A. For a weak acid, a higher pH increases ionization Which equation describes the rate of drug dissolution from a tablet? A. Fick's Law B. Henderson-Hasselbalch equation C. Michaelis-Menten equation D. Noyes-Whitney equation correct answer: D. The Noyes-Whitney equation describes the rate of drug dissolution from a tablet. Fick's first law of diffusion is similar to the Noyes-Whitney equation in that both equations describe drug movement attributable to a concentration gradient. The Michealis-Menten equation involves enzyme kinetics, whereas Henderson-Hasselbalch equations are used for determination of pH of the buffer and the extent of ionization of a drug molecule The pH of a buffer system can be calculated with A. the Henderson-Hasselbalch equation B. the Noyes-Whitney equation C. the Michealis-Mention equation D. Yong's equation correct answer: A. The Henderson-Hasselbalch equation form a weak acid and its salt is represented as pH = pka + log ([salt]/[acid]), where pka is the negative log of the dissolution constant of a weak acid, as [salt]/[acid] is the ratio of the molar concentration of salt and acid used to prepare a buffer If the pka of a drug is 5, at which of the following pH values do the ionic and nonionic forms of the drug exist at equal ratio?