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2435 CHM Experiment 5 Alkenes Iodine Number Report Sheet Part A. Data and calculations Oil/Fat used Mass of fat/oil - sample 1 Mass of fat/oil - sample 2 Concentration of Na2SO3 Fat titration 1 Initial volume in buret Final volume in buret to effect color change Volume of titrant used Name Date palm 0.27g 0.25 g 0.1 N 50.00 mL 21.20 mL 28.80 mL Fat titration 2 Initial volume in buret Final volume in buret to effect color change Volume of titrant used 50.00 mL 19.40 mL 30.60 mL Blank titration Initial volume in buret Final volume in buret to effect color change Volume of titrant used 35.00 mL 2.70 mL 32.30 mL Iodine Value Iodine Value - Sample 1 calculated as iodine value = 17.8 ( B S ) N 12.692 weight of sample where B=volume of blank, S=volume of titrant, N=normality of titrant [ ( 32.3 mL - 28.8 mL ) x 0.1 N x 12.692 ] / 0.27 g Iodine Value - Sample 2 Mean (or average) Iodine Value 12.7 15.3 QUESTIONS. 1. Draw the first step in the mechanism for the reaction of 2,3-dimethyl-2-butene with the Wijs reagent ( ICl ). + I Cl I + Cl I note that the -electrons in the double bond will attack the less electronegative element (the one with a partial positive charge on it). since chlorine is higher up in the periodic table, it is more electronegative so it is the iodine atom that is attacked. 2. What would be the effect on the iodine value if the KI solution was only 50% as concentrated as it should have been? Explain. the KI solution s role is to convert all of the remaining ICl to I2, which is then titrated with the thiosulfate solution. if the KI solution is only 50% of it s desired strength,not all of the KI will be converted to I2, and this will require less NaS2O3 solution than should be required. this will give an iodine value that is far too high (since in the equation it comes in as B - S ). 3. a. The Wijs reagent is approximately 0.22M ICl in acetic acid. How many moles of ICl are there in 25 mL?? (Recall that the units of molarity are moles / liter, and that you were given the volume in milliliters, not liters). Please show your work. 0.025 L x 0.22 moles / L = 0.0055 moles b. Now let s say you repeated this experiment on another day, and found that it took 70mL of the stock sodium thiosulfate solution to make your blank sample turn blue. Should this worry you at all? Why or why not? yes, since 70 mL is 0.070 mL x 0.1 moles / L = 0.007 moles. this is more S2O3 than should be required to titrate 0.0055 moles (it is a 1:1 relationship between S2O3 and I2) 4. Consider the fatty acids shown below, and use their structures to classify them in the appropriate below. categories (You can use a name more than once, but be careful as some of the names are very similar to each other). Saturated: arachidic acid, caproic acid, lauric acid Unsaturated: arachidonic acid, -linoleic acid, oleic acid, nervonic acid Polyunsaturated: arachidonic acid, -linoleic acid O HO arachidic acid 20 20:4 HO arachidonic acid 5,8,11,14 O O HO caproic acid 6 HO O HO lauric acid 12 O alpha-linoleic 18:3 9,12,15 O HO oleic acid 18:1 9 HO O nervonic acid 24:1 9 5. a. A short hand notation system for fatty acids is to write the total number of carbons in the acid, followed by a colon, then the number of double bonds, a delta sign, and the numbers for where the double bonds start. Write the short-hand for the fatty acids on the previous page by their names. b. Looking at all the short-hand descriptions of the fatty acids, what do you notice is common about ALL the fatty acids? (Do you see a trend?) they all have an even number of carbon atoms c. Looking now only at the unsaturated fatty acids (both short-hand descriptions and structures), what do you notice in common? (There should be more than one thing) the polyunsaturated fatty acids are not conjugated the first double bond usually occurs at either the 9th carbon, and then the other double bonds are separated by a CH2 unit, and occur one after another 6. a. Draw a fat that is made of 1 molecule of glycerol, 1 molecule of caproic acid, 1 molecules of caprylic acid (see 5a for shorthand), and 1 molecule of oleic acid. O O O O O O b. Are there other possible molecules that fit the description in part a, but are different compounds? Explain. yes, the order of the three fatty acids could change. for instance, above is drawn caproic, caprylic, and oleic; but it could be oleic, caproic, caprylic; or caproic, oleic, caprylic; or oleic, caproic, caprylic 7. What would be the difference between the iodine value of a fat made from 1 molecule of linoleic acid and 2 molecules of caprylic acid, AND a fat made from 2 molecules of oleic acid and 1 molecule of caprylic acid? (You do not have to calculate an iodine value to answer this question.) YES. 1 molecule linoleic acid + 2 molecules caprylic gives a fat with a total of 7 double bonds in it, while 2 molecules oleic acid and 1 molecule caprylic acid gives 4 double bonds. note however that fats made 1 one molecule of caproic and 2 molecules nervonic (2 double bonds) would have the same iodine value as 2 molecules caproic and 1 molecule caprylic (2 double bonds). the iodine value does not tell which fatty acids are present, only the total number of double bonds in the fat.

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