Chemistry Chemistry Chemistry Hl Essay

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Fats ANSWERS 1) Fats and oils can be described as esters of glycerol, C3H8O3. (a) (i) Draw the structure of glycerol. (i) CH2OHCHOHCH2OH; 1 (ii) Glycerol can react with three molecules of stearic acid, C17H35COOH, to form a triglyceride. Deduce the number of carbon atoms in one molecule of this triglyceride. 57 (1) (iii) A triglyceride is also formed in the reaction between glycerol and three molecules of oleic acid, C17H33COOH. State and explain which of the two triglycerides (the one formed from stearic acid or the one formed from oleic acid) has the higher melting point. (the one from) stearic acid; saturated / no (C to C) double bonds; chains pack close together / stronger intermolecular forces / van der Waals’ forces etc; 3 Ignore hydrogen bonding. If wrong choice made, only third mark can be scored. (3) (b) An oil sample containing 0.0100 mol of oil was found to react with 7.61 g of iodine, I2. Determine the number of C=C double bonds present in each molecule of the oil. (b) [pic]= 0.03 (mol) 3 (double bonds) (ECF); 2 Correct answer scores [2]. If 6 is given, with no working, award [1]. (2) [May 2006 SL P3] ER: In (a), the structure of glycerol was well known by the better candidates, although quite a number of alcohols with only one –OH group, or with more than one –OH group on the same carbon, were seen. A wide variety of answers to (a)(ii)was seen, predictably including 54. There were many errors seen in the stearic acid question, the most serious being the suggestion that C–C (or C=C) bonds were more easily broken. In part (b), there were inevitably many candidates who used the relative atomic mass instead of the relative molecular mass of iodine in the

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