# pre lab 4.docx - Pre-Lab 4 Determination of Ascorbic Acid...

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Pre-Lab 4: Determination of Ascorbic Acid in Vitamin C Tablets by Titration with Potassium Bromate (KBrO3) Introduction: In this lab we are looking to produce dehydroascorbic acid using bromine. To do this ascorbic acid will be oxidized and the following reaction will take place: This lab is conducted using the back titration method, a back titration is a method where we are able to determine the concentration of the analyte when reacting it with the known amount of excess reagent (2). To calculate the amount of bromide used in the reaction an excess amount of KBr will be added to an acidified solution (1). After the addition of this, they will then be titrated using KBrO3 using the following reaction: To calculate the total moles of Br2 in this reaction we have to calculate the number of moles of reacted with ascorbic acid plus the number of moles of Br2. Calculating the amount of Br2 requires the use of stoichiometry by converting I- to I2 we can quantitively solve this with the use of stoichiometry. A reaction between Br2 and I- take place which will produce I2 as follows:
How much of I2 that is produced during this reaction is determinant of a back titration which occurs with the standard thiosulfate solution. This solution is generated by the excess Br2 from