Question

32.67 mL   of a 0.1249 M   sodium hydroxide solution are required to completely react with a vitamin C tablet with a mass of  908 mg  . The potency on the bottle of vitamin C tablets is 500 mg. The molecular weight of vitamin C is 176.12 g/mol, and the molecular equation for the reaction is HC₆H₇O₆ (aq) + NaOH (aq) → NaC₆H₇O₆ (aq) + H₂O (l).

How many moles of OH^- are used in the titration?

How many moles of vitamin C are in the tablet?

How many milligrams of vitamin C are in the tablet?

What is the mass percent of vitamin C in the tablet?

Answer 1

#1. 1 mol NaOH yields 1 mol OH^-.

Moles of OH^- consumed = Molarity of NaOH x Volume of solution in liters

                                    = 0.1249 M x 0.03267 L

                                    = 0.004080483 mol

#2. Balanced reaction: C₆H₇O₆ (aq) + NaOH (aq) ----> H2O (l) + NaC₆H₇O₆ (aq)

Stoichiometry: 1 mol Vitamin C (ascorbic acid, C6H7O6) is neutralized by 1 mol NaOH.

So, at equivalence point, total number of moles of NaOH consumed is equal to total number of moles of ascorbic acid present in solution.

So,

Moles of vitamin C in tablet = 0.004080483 mol = Moles of OH^- consumed

#3. Mass of ascorbic acid = 0.004080483 mol x 176.12 g mol^-1

= 0.71865466596 g

#4. % Ascorbic acid in tablet = (Mass of ascorbic acid / Mass of sample) x 100

= (0.71865466596 g / 0.908 g) x 100

                                                = 79.15 %