Vitamin C investigation (volumetric analysis) Concentration (%m/m) of vit-C in the commercial tablets. Consider the bottle of vitamin-C tablets shown on the right. Using a 0.100 M NaOH standardised solution, what is the theoretical value of the average titre expected for the titration of one tablet? The balanced chemical equation for the reaction between ascorbic acid (vit-C) and NaOH is shown below. C6H8O6(aq) + NaOH(aq) --> NaC6H7O6(aq) + H2O(l) Solution Equipment - 3 X 200 mL conical flasks - mortar and pestle - phenolphthalein - Brand of Vit-C tablets - Stock solution of 0.100M NaOH - electronic balance - Burette (50mL) - funnel - retort stand - white tile - distilled water Step 1 Weigh a 200 mL conical flask. Record its mass in table1. Step 2 Crush a Vitamin C tablet into a fine powder using a mortar and pestle. Step 3 Place the crushed vitamin tablet in the conical flask and reweigh. Record the result in table 1. Step 4 Place approximately 30-40 mL of distilled water and completely dissolve the powder. Step 5 Fill the burette with the 0.100M standardised solution of NaOH. Record the burette reading in table 2. Step 6 Place two or three drops of indicator in the the conical flask and titrate against the standard solution until the end point. A permanent colour change of the solution in the conical flask indicates the end point. Step 7 Take the final reading from the burette and record the result in table 2. Step 8 Repeat steps 1-7 twice more. 1. Calculate the mass of vit-C (molar mass 176 g/mol) for each trial . Record, the result in table 3. 2. Calculate the concentration (%m/m) of vit-C (molar mass 176 g/mol) for each trial . Record, the result in table 4 . 3. Are the results repeatable and reproducible? Explain. 4. Are the results reliable? Explain 5. View the label shown on the right from the container of the brand of Vitamin-C tablet. What can you say about the validity of the results? Solution Questions you may wish to investigate. 1. Do all fresh citrus fruit have the same %(m/m) of ascorbic acid (vitamin-C)? 2. How does boiling vegetable impact on the vitamin-C content of the food? 3. Does heat destroy vitamin-C? 4. How does the content of a cheap generic brand of orange juice compare with a similar well known Brand? 5. When cooking vegetables which method is better in preserving vitamins, steaming or boiling?