DETERMINATION OF ASCORBIC ACID CONTENT IN VITAMIN C TABLETS
To calculate the mass of the ascorbic acid and hence the mass percentage of ascorbic acid in the vitamin C tablet.
(Refer to Lab Manual)
1. Accurately weight vitamin C (effervescent type) in a 50 ml beaker. Add about 30 ml of deionised water to dissolve the vitamin C tablet. Once the tablet has dissolved completely, transfer the solution into a 250 ml volumetric flask via a plastic filter funnel. Rinse the beaker twice with some deionised water and transfer the washings into the volumetric flask. Rinse the filter funnel as well. At this point, more water is added carefully until the bottom of the meniscus is right on the line. Stopper the flask and complete the mixing by repeated inversions with swirling and shakings in between. Keep your hand on the stopper at all times lest it falls out (or leaks)! 2. Using a 25 ml transfer pipette, transfer 25ml of the vitamin C solution into a 250ml Erlenmeyer (conical) flask. To the conical flask, add 50 ml of the water (use a 100 ml measuring cylinder), 5ml 4% (w/v) KI solution (use a 5ml measuring pipette), 2ml of 3% (v/v) CH3COOH solution (use a 2ml measuring pipette), and finally, 5 drops of starch solution. Place a white tile underneath the flask. 3. Fill the 50ml burette with 0.01M N-bromosuccinimide (NBS). If there is any air bubbles trapped in the column, gently tap the burette to dislodge the bubbles. Check that there is no leakage before you do the titration. 4. Before titration, record the initial burette reading. The end point is reached when 1 drop (or less) of N-bromosuccinimide causes the solution to turn a permanent yellow- green or blue color (the actual color being dependent on the concentration of the starch). Record the final burette reading. 5. Repeat the titrations 3 more times (use the same conical flask – discard the contents from the previous titration and rinse the flask...
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