The Kool-Aid Acid Test Part B - Back to Part A

o get an idea of how titrations can be useful, consider Figure 2. Assume that 0.70 g of a drink mix powder was used to make the acidic solution and that the drink mix contains citric acid (molar mass 192g/mol).

Clearly, there is a point in the titration where the pH makes a sudden jump.  To locate the exact point of equivalence, find the point of inflection, where the slope of the curve is greatest (or where the curvature changes from convex to concave).  In this case, the inflection point, and equivalence, is when 23.25mL of 0.40 M NaOH has been added. Moles of base at the equivalence point can be determined from the volume of base delivered to reach the equivalence point and the concentration of NaOH.

2. Using the fact that the acid and base are in exact stoichiometric proportions at the equivalence point, calculate the moles of citric acid in the solution.  The balanced equation is:

H₃C₆H₅O₇ (aq) + 3NaOH ➞ Na₃C₆H₅O₇ (aq) + 3H₂O (l)

3. Now calculate the mass of citric acid in the drink mix.

4. Calculate the mass percent citric acid in the drink mix.