Question

1. (5 pt.) Soon you will synthesize the analgesic acetanilide in lab. It’s m.p. is 114C. What does it indicate about your product if you obtain a m.p. of 103 - 112C. Explain.

2. (6 pt.) Neither aniline nor nitrobenzene is particularly water soluble. However, one is completely soluble in dilute aqueous HCl. Which one is soluble, and explain why? (For maximum credit, provide a chemical equation for your answer.)

3. (5 pt.) Name the two adsorbents that are most used on TLC plates or in column chromatography.

4. (4 pt.) What steps should be taken to obtain the melting point of a solid compound that decompose before reaching the melting point?

5. (8 pt.) Indicate which one of the following molecules are polar or nonpolar

6. (8 pt.) TLC of the two compounds using hexane-ethyl acetate (8:2) is given: (a) Indicate each spot belongs to which compound? (b) Calculate the Rf values for each compound. Show your work.

7. (4 pt.) What two methods were used to visualize the spots on the developed TLC plate?

8. Considering the given two component liquid mixture phase diagram, answer the following questions: a. (3 pt.) What are the boiling points of A and B, respectively? b. (2 pt.) Which line (X1, X2, or X3) represents an evaporation step in a distillation process? c. (3 pt.) When a mixture of 30% A and 70% B boils, what will be the composition of the vapor above the liquid? Show your work.

9. (6 pt.) 2.56 g of benzyl alcohol was reacted with 5.92 g of sodium chloride. Upon work up, 1.87 g of benzyl chloride was obtained. Sulfuric acid is a catalyst and should not be considered for this calculation. The stoichiometry of the reaction is 1:1  1. What is the limiting reagent? Calculate the theoretical and the percent yield. Show all calculations. (atomic weights, C = 12.011, H = 1.0079, O = 15.9994, Cl = 35.45, Na = 22.99).

Answer 1

1) Pure product has melting point of 114°C. We know, when impurities are present in the solid compound the melting point decreases and the melting range increases rather than a sharp melting point. As the observed melting point is 103-112, we can say that melting point is decreased and the range is too broad compared to sharp melting point of pure compound. Hence this concludes that the obtained sample is contaminated with some impurities. 2) NH NH, CÓ + HCI — Aniline reacts with HCl to form an anilinium chloride salt. This is soluble in water as it is an ionic compound. 3) Often in TLC, silica and alumina are used as a satationary phase. 4) If solid decompases before reaching to the melting point, then we can note the temperature at which the solid decomposes. This will be called as decomposition temperature. 5) No molecules are given. 6) No TLC is shown hence may not be possible to calculate Rf values. 7) 1) iodine complex and 2) UV elumination.

8) No phase dig. is given. H2SO4 OH + NaCl Number of moles of benzyl alcohol = mass/molar mass = 2.56 g/108.14g/mol = 0.02367 mol Number of moles of Naci = 5.92 g / 58.44 g/mol = 0.1013 mol Thus NaCl is in excess and limiting reagent is benzyl alcohol. theoretical yield = 0.02367 mol*molar mass of product = 0.02367*126.58 = 3.00 g Practical yield = 1.87 g % yield = (practical / theoretical yield)* 100 % yield = (1.87/3.00)*100 = 62.33 %