a 0.120 M solution of an A 0.120 M solution of an enantiomerically pure chiral c

Question

a 0.120 M solution of an A 0.120 M solution of an enantiomerically pure chiral compound D has an observed rotation of +0.12^4 in a 1-dm sample container. The molar mass of the compound 178.0 g/mol. What is the specific rotation of D? Number deg mL/g middot dm b) What is the observed rotation if this solution is mixed with an equal volume of a solution is 0.120 M in L, the enantiomer of D? Number deg What is the observed rotation if the solution D is diluted with an equal volume of solvent? Number deg (d) What is the specific rotation of D after the dilution described in part (c)? Number deg ml/g middot dm What is the specific rotation of L, the enantiomer of after the dilution described in part (c)? Number deg mL/g middot dm What is the observed rotation of 100 mL of solution that contains 0.01 mole of D and O.005 mole of L? (Assume a 1-dm path length.) Number deg

Explanation / Answer

a)

concentration = 0.120 x 178 / 1000

                       = 0.02136 g/ L

specific rotation = observed rotation / length x concentration

                          = 0.12 / 1 x 0.02136

specific rotation = 5.62 deg .mL / g.dm

b)

equal volumes of equal concentrations of enantiomers mixed.solution is racemic mixture

observed rotation = 0 deg

c)

volume is doubled , concentration is halved.

concentration = 0.02136 / 2 = 0.01068 g/ L

observed rotation = 5.62 x 1 x 0.01068

                          = 0.06 deg

d)

specific rotation is uneffected by dilution .

specific rotation = 5.62 deg .mL / g.dm

e)

specific rotation of L = - 5.62 deg .mL / g.dm

f)

observed rotation = 0.05 oC

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