A Biochemist Wishes to Study the Activity of an Enzyme

Multiple Choice

A biochemist wishes to study the activity of an enzyme that produces one mole hydrogen ion for every mole of product produced. However, the enzyme is sensitive to changes in pH and will become inactive at pH less than 7.1. If the initial pH of the solution is 7.21 set with a phosphate buffer (the pK_a's of the three acid-conjugate base pairs derived from phosphoric acid, H₃PO₄, are 2.12, 7.21 and 12.32) and the reaction is designed to produce 0.15 moles of product in a volume of 250 mL, what is the minimum concentration of the conjugate acid in the buffer solution?

A) 0.46 M
B) 0.53 M
C) 0.82 M
D) 1.12 M
E) 1.25 M