Iodine Test Standard Solutions

Hydrochloric Acid Solution (5% by weight): 1) Add 70ml of concentrated hydrochloric acid to a 1000ml beaker 2) Add 550ml of distilled water and mix well. 3) A accurately graduated 1000ml or 500ml cylinder must be used for the measurement of volume. Sodium Thiosulfate (0.100N): 1) 24.820gms of sodium thiosulfate is dissolved in 75+-2.5mL of freshly boiled distilled water in a 500ml beaker. 2) 0.10+-0.01g of sodium carbonate is added to minimize bacterial decomposition of the thiosulfate solution. 3) Carefully and completely transfer the mixture to a 1000ml volumetric flask (Standard Measuring Flask SMF) and dilute to the mark. 4) Allow the solution to stand at least 4 days before standardizing. 5) The solution should be stored in an amber bottle. Standard Iodine Solution (0.100+-0.001N): 1) Weigh 12.700g of iodine and 19.100g of potassium iodide (KI) into a 500ml beaker. 2) Mix the dry iodine and potassium iodide. 3) Add 2 to 5 mL of water to the beaker and stir well. 4) Continue adding small increments of water (approximately 5 ml each) while stirring until the total volume is 50 to 60 ml. 5) Allow the solution to stand a minimum of 4hrs to ensure that all crystals are thoroughly dissolved. Occasional stirring during this 4hrs period will aid in the dissolution. 6) Quantitatively transfer to a 1000ml volumetric flask and fill to the mark with distilled water. 7) It is important that the standard iodine solution has an iodide-iodine weight ratio of 1.5 to 1. 8) Store the solution in an amber bottle. Potassium Iodate Solution (0.1000N): 1) Dry 4 or more grams of primary standard grade potassium iodate (KIO3) at 110+-5C for 2h and cool to room temperature in a desiccator. 2) Dissolve 3.5667+_0.1mg of the dry potassium iodate in about 100mL of distilled water. 3) Quantitatively transfer to a 1000ml volumetric flask and fill to the mark with distilled water. 4) Mix thoroughly and store in a glass-stoppered bottle.