BIOCHEMISTRY LAB 7 REPORT 2023| PORTAGE LEARNING|WITH PROCEDURES, EXPLANATION AND FINAL RESULTS.HIGHLY RECOMMEDED CHEM 212: Organic Chemistry Lab 7 - Polarimetry Assigned reading : Mohrig 4th Edition, Chapters 17.1-17.3, Karty Chapter 5 sections 5.1, 5.2 and 5.11. Assigned exercise : Look up the structures of the following carbohydrates D -Fructose, Sucrose and Maltose. Write down the formula for the calculation of specific rotation given the observed rotation, path length and concentration of a chiral sample. Background: A molecule that does not possess an internal mirror plane of symmetry and is not superimposable on its mirror image is said to be chiral. Optical activity is the ability of chiral molecules to rotate plane -polarized light. The degree to which an optically active substance rotates light may be used to determine a) the identity of the substance, b) the enantiomeric purity of the substance or c) the concentration of t he substance in a solution. Optical activity can be measured using a polarimeter, which measures the degree of rotation of plane polarized light as it passes through an optically active sample. The specific rotation [α] of a compound is a fixed physical pr operty of that compound (like its boiling point or melting point or density). And knowing the observed rotation, concentration of the sample in solution and length of the cell, the specific rotation can be calculated. In this lab you will learn how to meas ure the optical rotation of an unknown sample, calculate its specific rotation and thereby identify your unknown. Equipment/Materials: Volumetric flasks and polarimetry cuvettes, an unknown chiral compound (an optically active sugar) and DI water. Waste Disposal : The aqueous sugar solutions are non-toxic and may be discarded down the sink. Any leftover solid goes in the solid waste. Procedure You will be provided with ~0.2 g of an unknown chiral compound. Weigh and record its weight accurately in your lab notebook. Place your unknown in a clean 50 mL beaker and dissolve it in 3 mL of DI water. Swirl the contents until all the solid has dissolved. Carefully transfer this solution to a 10 mL volumetric flask. Rinse the beaker with approximately 2 mL of D I water and transfer it to the volumetric flask. Rinse again with 2 mL more of DI water and transfer to the volumetric flask. Now add DI water carefully to the volumetric flask containing the unknown solution until the bottom of the liquid meniscus is exac tly on the line. If you add too much water and overshoot the line, the solution will have to be discarded and you will have to start over. Stopper the volumetric flask and invert it several times (being careful not to spill any of the solution) to ensure thorough mixing of the contents. Note the volume in your notebook. Calculate the concentration in g/mL. Obtain the αobs by analyzing your solution in the polarimeter following the instructions provided by your TA. Get your formu la for specific rotation calculation approved by your TA. Calculate the specific rotation for your unknown sugar. Compare it to the specific rotation values provided below for the possible unknowns and identify your unknown. Possible Unknowns and their spe cific rotation values: D-Fructose (-86), Sucrose (+64.5) and Maltose (+118) Post-lab review: Discuss the following with the class : Plane polarized light, optical activity, observed rotation, specific rotation, enantiomers diastereomers and racemic mixtures.
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