Prelab 6 - CHEMISTRY PDF

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CHEMISTRY...

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Title: Determination of Ascorbic Acid in Vitamin C Tablets by Titration with Potassium Bromate

KBrO ¿ ) ¿ ¿

The purpose of this lab is to determine how much ascorbic acid is in a Vitamin C tablet. The production of Bromine is accomplished by adding excess KBr to an acidified solution of the sample and titrating with KBrO3 . When all of the ascorbic acid has reacted, excess Bromine is indicated by a faint yellow color. To determine the amount of excess Bromine we can use stoichiometric analysis to −¿ convert an excess of I ¿ to I 2 Materials: 50 commercially available non-chewable Vitamin C tablets for the unknown, 1 gram of Starch for 500mL starch indicator, 12 grams of sodium thiosulfate ( Na2 S2 O 3 ×5 H 2 O ) for 1L 0.05 M STD. solution, 2.5 Liters of 1.5M H 2 SO 4 , 250 grams of KBr, 150 grams of Iodate-free KI and mortar. Safety Na2 S2 O 3 - Not classified for physical or health hazards H 2 SO 4 -May be corrosive to metals, causes severe skin burns and eye damage KBr - Irritant, environmentally damaging, causes skin irritation, serious eye

irritation, may cause respiratory irritation. Iodate-free KI- Causes damage to organs after repeated exposure Procedure Grind and homogenize 4 Vitamin C tablets in a mortar and transfer to weighing paper

Weigh 3 inidividual samples of vitamin C powder to 0.45-0.5 grams each

Transfer each sample to a 250mL Erlenmeyer flask

Obtain 2 burette and prepare for titration by rinsng with distilled water

Rinse burette 1 with 10mL of standard KBrO3 solution and then fill burette with KBrO3

Rinse butette 2 with 10mL of standard sodium thiosulfate solution and then fill burette with sodium thiosulfate solution...