Determination of iodine values.

. First, the experimental purpose is1. Master the principle and operation method of measuring iodine value.
2. Understand the significance of measuring iodine values.
2, experimental principle
the fat in the carbon chain of unsaturated fatty acids have unsaturated bonds, can absorb halogens (Cl2, Br2 or I2), the more unsaturated bonds, the more halogens absorbed. Every 100 grams of fat, the number of grams of iodine absorbed under certain conditions, is called the iodine value of the fat. The higher the iodine value, the higher the content of unsaturated fatty acids.
iodine value is within a certain range for a grease product. The lyic acid produced in the oil industry is the raw material of rubber synthesis industry, the acid is an important raw material for the medical treatment of hypertension drugs, they are unsaturated fatty acids, while another type of products such as stearic acid is saturated fatty acid. If the product is mixed with some other fatty acid impurities, its iodine value will change, so the iodine value can be used to indicate the purity of the product, while calculating the quantitative composition of oil and fat. In production, iodine values are often measured, such as determining the degree to which products are separated and de-miscellaneous (i.e. unsaturated fatty acid impurities).
the experiment used sodium sulfate to titrate excess potassium bromide and potassium iodide reaction released iodine, in order to obtain the amount of iodine added to the fat.
Ibr-KI → KBr-I2
. The I2 plus 2Na2S2O3→ 2NaI plus Na2S4O6
the most appropriate sample, iodine value and action time have a certain relationship.
, instruments and
reagents instruments
iodine titration bottle (250 to 300mL), or with plug conical bottle instead,
measuring barrel
(10) , 50mL), sample tube (about 0.5cm in diameter, 2.5cm in length),titring tube
(50mL), analysis of
balance
or torque balance.
reagents
. 1. Hanus solution: take 12.2g iodine, put it in a 1500mL conical bottle, slowly add 1000mL ice acetic acid (99.5%), shake while shaking, while slightly warm, so that iodine dissolves. After cooling, add about 3 ml of bromine.
: Ice acetic acid should not contain reduced substances. Take 2 ml of ice acetic acid, add a little potassium chromate and sulfuric acid. If it is green, the presence of a reduced substance is proved.
2. 0.05mol/L standard sodium sulfate solution: 50g of crystalline sodium sulfate is placed in distilled water cooled after boiling (no CO2 present). Add borax 7.6g or sodium hydroxide 1.6g. (Sodium sulfate solution is most stable at pH9 to 10). After dilution to 2000mL, the standard 0.02mol/L potassium iodide solution was pressed to calibration:
accurately measured 0.02mol/L potassium iodide solution 20mL, 10% potassium iodide solution 10mL and 0.5mol/L sulfuric acid 20mL, mixed evenly. The 1% starch solution was used as an indicator and the sodium sulfate solution was used for calibration. After calculating the concentration of sodium sulfate solution according to the following reactive formula, the water was diluted to 01mol/L.
3. Pure carbon tetrachloride
. 4. 1% starch solution (dissolved in saturated sodium chloride solution)
5. 10% potassium iodide solution
6. Peanut oil or lard
4, operating steps
with glass tube (about 0.5 cm ×2.5 cm) accurately weigh 0.3 to 0.4 g peanut oil (or about 0.1 g castor oil, about 0.5 g lard) 2 servings. Place the sample and tube together in two
driding
iodine value measuring bottles (1) and do not stick the oil to the bottleneck or wall. Add 10 ml of carbon tetrachloride and shake gently to dissolve all the oil.
carefully add 25 ml of Hanus solution to each iodine value measurement bottle with a titration tube, so that the solution is not exposed to bottlenecks. Plug the glass plug, add a drop of 10% potassium iodide solution between the glass plug and the bottle mouth to close the gap, to prevent iodine sublimation spillage caused by measurement errors. Then, place in the dark for 30 minutes at 20130 degrees C.
Based on experience, the iodine value is determined to be less than 110 grease when placed for 30 minutes, the iodine value above this value needs to be placed for 1 hour; Shake from time to time during placement. The brine addition reaction is reversible and can only be carried out completely if the halogen is absolutely excessive. Therefore, the oil should not absorb more than half the amount of iodine contained in hanus solutions. If the color of the mixture in the bottle is very shallow, indicating that the amount of oil is too much, should be called a small amount of oil, redo.
30min, immediately carefully open the glass plug so that potassium iodide solution next to the plug flows into the bottle and is not lost. With the newly made 10% potassium iodide 10mL and distilled water 50mL, the liquid on the glass plug and bottleneck is flushed into the bottle and mixed. The solution of 0.05mol/L sodium sulfate was quickly titrated to the bottle with a light yellow solution. Add 1% starch about 1mL and continue titration. Near the end point, the iodine is oscillat by force, allowing iodine to enter the aqueous solution from carbon tetrachloride. Drop until the blue disappears, i.e. reach the titring end point. Force oscillation is one of the keys to success or failure of titration, otherwise it is easy to drop too much or not enough. If the oscillation is not sufficient, the carbon tetrachloride layer appears purple or red, and the force oscillation is continued so that all iodine enters the water layer.
the titration has been placed for some time, the titration should return to blue, otherwise it indicates excessive titration (why?). )。 Another two blank control, in addition to not refueling samples, the rest of the operation is the same. After titration, pour the waste liquid into the waste bottle in order to recover carbon tetrachloride.
: The instruments used in the experiment, including iodine measurement bottles, measuring tubes, titration tubes and glass tubes for samples, must be clean and dry.5, the calculation of theiodine value represents 100 grams of fat can absorb the number of grams of iodine, so the sample's iodine value is calculated as follows:
A - titration blank with the average number of milliliters of sodium sulfate solution used
; - Average number of milliliters of sodium sulfate solution used for titration samples;
C - the weight of the sample;
T - the number of grams of iodine equivalent to 1 ml of 0.05mol/L sodium sulfate solution.
the iodine values of fatty acids and other lipids, the method of operation is exactly the same. .