Enter the angle through which plane-polarized light is rotated, the mass concentration of the solutions, and the path length.

## Specific Rotation Formula

The following formula is used to calculate the specific rotation.

SR = a/(y*l)

- Where SR is the specific rotation (deg*mL/(g*dm))
- a is the angle through which plane-polarized light is rotated (degrees)
- y is the mass concentration (g/mL).
- l is the path length (dm)

To calculate specific rotation, divide the angle by the product of the mass concentration times the path length.

## Specific Rotation Definition

**What is specific rotation? **A specific rotation is defined as “the change in orientation of monochromatic plane-polarized light, per unit distance-concentration product, as the light passes through the sample of a compound in solution.” (Source)

## Example Problem

How to calculate specific rotation?

**First, determine the angle.**For this problem, the angle through which the light is rotated is 25 degrees.

**Next, determine the mass concentration.**In this example, the mass concentration of the compound in the solutions is 50g/mL.

**Next, determine the path length.**In this example, the total length of the path is 3dm.

**Finally, calculate the specific rotation.**Using the formula above, the specific rotation is found to be 25/(50*3) = .1666

- (deg*mL*g^-1*dm^-1)

## About Specific Rotation

**Is specific rotation concentration dependent? **A specific rotation is dependent on the mass concentration of the compound in the solution.

**Can specific rotation be negative? **A specific rotation can be negative if the rotation counterclockwise is considered negative. The absolute specific rotation will always be positive.