CA1 Ans Key

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Start: The melting point composition diagram for substances, Aand B, is provided below. The molecular weight of A = 113.45 g/mol and that of B = 60.18 g/mol. Use the diagram and corresponding information to answer questions 1 and 2: 2 23 8 88 i i N N i i 0.1 0.3 0.5 0.7 0.9 Mole Fraction B 1. What is the melting point of the eutectic mixture of A and B? (1.5 pts) 2. What is the melting point of a sample obtained from a mixture of 3.97 g of compound A and 0.903 g of compound B? (2 pts) A. 87°C B. 52°C @ 81°C " 75°C E. 96°C 3. Which of the following statements is NOT True (false) with regards to melting point of a compound? (1.5 pts) A. If the addition of a known compound Y Iowers the melting point of an unknown sample X, then X and Y cannot be identical. B. If the addition of a known compound Y to an unknown sample X does not lower the melting point of X, then X must be identical to Y. A sharp melting point for a crystalline organic substance always indicates a pure single compound. D. Impurities in a sample compound always lowers the melting point of an organic compound. Scanned with CamScanner

Aftera _sy"thESis experiment you obtain a sample of product on which you do a melting point determination and find a melting point range of 114 to 125 degrees Celsius. The sample is Supposed to be acetylsalicylic acid. (Pure acetylsalicylic acid melts at 135 degrees Celsius). Use this information to answer questions 4 to 6: 4. What preliminary conclusion(s) can you reach from this one determination? Identify ALL statements that are TRUE. (2 pts) A. The sample is not acetylsalicylic acid. : i (B.) The sample may be acetylsalicylic acid. (C) The melting point determination may need improvement — it may not have been done properly, and make sure it was repeated at least once. The sample is probably impure. E. The sample is acetylsalicylic acid. 5. After purifying the sample from question 4 -, you find it melts sharply at 135 degrees Celsius. Now what conclusion(s) can you reach? Identify ALL statements that are TRUE. (1.5 pts) A. The melting point determination may need improvement — it may not have been done properly, and make sure it was repeated at least once. € B. The sample is probably impure. b The sample may be acetylsalicylic acid. s D. The sample is not acetylsalicylic acid. E. The sample is acetylsalicylic acid. 6. You mix the sample discussed in question 4 and question 5, with another sample, which you know to be pure acetylsalicylic acid. You grind the mixture thoroughly with a mortar and pestle and do a melting point determination on the mixed product. You now observe melting over a range of 126 to 131 C. Now what conclusions can you reach regarding the original product? (1.5 pts) ) i The sample is not acetylsalicylic acid. B. The sample is acetylsalicylic acid. C. The sample may be acetylsalicylic acid. Scanned with CamScanner

Match the following pieces of equipment applied in filtration processes to their corresponding functions described in questions 7 to 9. A. VacuumfFilter) trap C. Fluted filter paper B. Stemless conical D. Buchner funnel funnel E. Filter flask 7. An evacuated flask in which the filtrate is contained during a vacuum filtration process. (1.5 pts) £ 8. A setup the ensures that no fluids are carried over from the aspirator or from the vacuum source to the evacuated flask. (1.5 pts) A 9. An equipment that retains the sample isolated by vacuum filtration and trapped by a filtering medium. (1.5 pts) D 10. Which of the factors listed below would affect retention factor (RF) value in TLC chromatography? Identify ALL statements that are TRUE (2 pts) Q Functional groups on the compound being analyzed (B.) Amount of sample spotted (C) The solvent system D. Length of the TLC plate ) E. Allthe above A colorless unknown substance is spotted on a TLC plate and developed in the appropriate solvent system. The spots do not appear when visualization with UV lamp is attempted. Which of the listed methods could be applied to visualize the spots if the compound is; 11. Ketone — [Methyl ethyl ketone] (1.5 pts) D 12. Alkene - [ 1-Butene] (1.5 pts) 6 lodine vapors Potassium permanganate solution Bromocresol Green solution 2,4 dinitro phenyl hydrazine solution o0 ®>» Scanned with CamScanner | | | | | |

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The scheme shown below outlines the procedure used to separate a benzoic acid and benzophenone. CrNHz ©/COOH O I O In methylene water cyclohexamine NaHCO;3 benzoic acid benzophenone A AT P e mixture of cyclohexamine, methylene " M 2M HCl 13. What is the identity of component V? (1.5 pts) A. Benzoic acid B. Sodium benzoate Cyclohexylammonium chloride D. Cyclohexamine E. Benzophenone methylene 14. Of the reagents listed below which one would fit the identity of reagent S (1.5 pts) A. 3M acetic acid B. 20% Sodium Hydroxide base C. 10% Sodium bicarbonate base 6M Hydrochloric acid E. Methylene chloride Scanned with CamScanner

enzoic acid contaminated with acetanilide, you 9% composition of the acetanilide impurity t in mL of solvent (water) required for the 15. In recrystallization from boiling water of b begin with an impure sample of 4.2 grams. If the in the sample is 2.5 %, what is the minimum amoun recrystallization? (2 pts) Compound Solubility in water at 25C solubility in water at 100C Benzoic Acid 0.34 g/100mL 5.6 g/100mL Acetanilide 0.53 g/100mL 5.5g/100 mL A. 1015 ml B. 792 ml 75 ml D. 73ml E. 1235ml 16. If the recrystallized material from question 15 is isolated by vacuum filtration, calculate the 9% recovery of benzoic acid for this recrystallization process. (2 pts) A. 100 % B. 87% 94 % D. 92% E. 97% 17. Calculate the amount of compound A, that would be extracted into 8.0 mL of diethyl ether after one extraction of 7.00 g of a compound A is dissolved in 12.5 mL of water. The distribution coefficient (Kd) of compound A in diethyl ether and water is 3.5. (2 pts) C. 39¢g D. 5.12¢g i E. 6.44g &, 18. If the extracted amount of compound A from guestion 17 is recovered by separating the diethyl ether layer from the water layer [using a separatory funnel] and then evaporating diethyl ether, calculate the % recovery of A for this extraction process. (1.5 pts) (n.) 69 % B, 71% C. 57% .‘ D. 73% & E. 92% End o~ L Scanned with CamScanner

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