Things You'll Need:
- Stearic acid Carbon tetrachloride Wijs solution 1 Erlenmeyer flask, 500ml 1 Glass stoppered volumetric flask, 1000 ml. Pipettes with a capacity range of 5, 20 and 25 ml. Oven Hot plate A.C.S grade glacial acetic acid Potassium iodide (A.C.S or AR grade) Chlorine, 99.8% purity Soluble starch. Potassium dichromate, ground and dried Sodium thiosulfate
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Step 1
Collect all the apparatus and reagents so that you will have them handy when you begin the test. Clean the glassware and dry it in a mid-temperature oven.
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Step 2
Heat the hot plate to a temperature of 50 to 60-degrees Fahrenheit (10 to 15-degrees centigrade). Place the stearic acid sample on the hot plate and melt it.
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Step 3
Pour 20 ml of carbon tetrachloride into a 500 ml Erlenmeyer flask. Weigh the stearic acid sample and add it to the same Erlenmeyer flask. Pipet 25 ml of the Wijs solution into the flask. Stopper the flask and swirl it to insure a thorough mixture.
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Step 4
Prepare and conduct at least 2 blank determinations with each group of samples simultaneously and similar in all respects.
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Step 5
Store the flask in a dark place for half an hour, at a temperature ranging between 70 to 85-degrees Fahrenheight (20 to 30-degrees Celsius). Remove the flask from the dark storage and add 20 milliliters of potassium iodide solution followed by 100 milliliter of distilled water.
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Step 6
Titrate against 0.1 normality sodium thiosulfate, adding it gradually and with constant, vigorous shaking. You should carry out the titration to the end point, which is determined by the discoloration of the solution, at which time the yellow color almost disappears.
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Step 7
Add 1 to 2 milliliters of starch indicator solution and continue the titration until the blue color has just disappeared.
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Step 8
Record the values and use the calculation in the diagram to calculate the iodine value of the stearic acid sample:
B = Titration of blank
S = Titration of sample
N = Normality of sodium thiosulfate solution.
