Question

Which of the following statements is correct about a racemic mixture of R-lactic acid and S-lactic acid?

A. The mixture rotates plane-polarized light with an angle of rotation.
B. Both compounds are achiral, and the mixture is optically inactive.
C. When a chiral reagent is added to the mixture, two diastereomers are formed.
D. R-lactic acid and S-lactic acid can be isolated from the racemic mixture directly.

Answer 1

A racemic mixture of R-lactic acid and S-lactic acid is optically inactive and does not rotate plane-polarized light. It cannot be separated directly into R-lactic acid and S-lactic acid without the addition of a chiral reagent. Adding a chiral reagent to the mixture would result in the formation of two diastereomers.

Step-by-step explanation:

A racemic mixture of R-lactic acid and S-lactic acid is optically inactive, meaning it does not rotate plane-polarized light. This is because the R and S enantiomers of lactic acid have equal and opposite rotations, resulting in a net rotation of zero.

A racemic mixture is formed when equal amounts of both enantiomers are present. It cannot be separated directly into R-lactic acid and S-lactic acid without breaking chemical bonds. In order to separate the enantiomers, a chiral reagent needs to be added, which would result in the formation of two diastereomers.