Answer: Fat and oil are names for the same class of

Chapter 24, Problem 24.74

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Fat and oil are names for the same class of compounds, called triglycerides, which contain three ester groups CH2OOOCOR A A A CHOOOCOR A A A CH2OOOCOR O B O B O B A fat or oil where R, R9, and R represent long hydrocarbon chains. (a) Suggest a reaction that leads to the formation of a triglyceride molecule, starting with glycerol and carboxylic acids (see p. 474 for structure of glycerol). (b) In the old days, soaps were made by hydrolyzing animal fat with lye (a sodium hydroxide solution). Write an equation for this reaction. (c) The difference between fats and oils is that at room temperature, the former are solids and the latter are liquids. Fats are usually produced by animals, whereas oils are commonly found in plants. The melting points of these substances are determined by the number of CC bonds (or the extent of unsaturation) presentthe larger the number of CC bonds, the lower the melting point and the more likely that the substance is a liquid. Explain. (d) One way to convert liquid oil to solid fat is to hydrogenate the oil, a process by which some or all of the CC bonds are converted to CC bonds. This procedure prolongs shelf life of the oil by removing the more reactive CC group and facilitates packaging. How would you carry out such a process (that is, what reagents and catalyst would you employ)? (e) The degree of unsaturation of oil can be determined by reacting the oil with iodine, which reacts with the CC bond as follows: I I A A A A A A A A OCOCPCOCO + I2 88n OCOCOCOCO A A A A A A The procedure is to add a known amount of iodine to the oil and allow the reaction to go to completion. The amount of excess (unreacted) iodine is determined by titrating the remaining iodine with a standard sodium thiosulfate (Na2S2O3) solution: I2 1 2Na2S2O3 Na2S4O6 1 2NaI The number of grams of iodine that react with 100 grams of oil is called the iodine number. In one case, 43.8 g of I2 were treated with 35.3 g of corn oil. The excess iodine required 20.6 mL of a 0.142 M Na2S2O3 for neutralization. Calculate the iodine number of the corn oil.