To employ titration technique to determine the content of vitamin C in commercial tablets using volumetric analysis and compare it with the manufacturers' specifications.
Deficiency of essential antioxidant Vitamin C in human will lead to scurvy. In this experiment, the vitamin C content of commercial tablets is determined and then compared with the manufacturers' specifications. Vitamin C, ascorbic acid C6H8O6, reacts with iodine and is oxidised to dehydroascorbic acid rapidly in acidic medium.
Considering iodine is only slightly soluble in water, the above titration cannot be performed directly by a standard iodine solution because of the insignificant end point. Thus, alternative method, back titration, will be employed. Two equations are involved.
First, standard potassium iodate(V) (KIO3), potassium iodate(KI) and dilute sulphuric acis(H2SO4) react to find out the excess quantity of iodine. Below shows the equation.
Second, the iodine generated reacts with ascorbic acid immediately. While the excess iodine is the titrated by standardized sodium thisulphate(Na2S2O3) as shown the equation below. Then, the iodine reacted with ascorbic acid can be determined followed by the content of ascorbic acid.
Starch indicator is added for the determination of the end point of the titration. Starch reacts with excess iodine in solution to form the blue-black starch-iodine complex. Thus, the colorless solution indicates there is no iodine in the solution.
A) Preparation of standard potassium iodate(V) solution
1)A weighing dish was weighed. 0.6g of potassium iodate(V) was added to the weighing dish carefully with a spatula. The mass of the weighing dish with potassium iodate(V) was weighed. The mass was recorded.
2)The potassium iodate(V) was poured from the weighing dish to a clean and dry 100cm3 beaker.