Question

Question:A solution of an unknown compound (3.0 g of the compound in 200 mL of solution), when placed in a polarimeter tube 2.0 dm long, was found to rotate

the plane of polarized light 18° in a counterclockwise direction. What is the specific rotation of the compound?

Short answer

Specific rotation of the compound is -60.

Step-by-step solution

Explanation of formula

The specific rotation at aspecified temperature and wavelength can be calculated from the observed rotation using the formula,

Where,

[𝜶] = the specific rotation,

T= temperature in degrees Celsius,

l =is the wavelength of theincident light (when the sodium D-line is used,lis indicated as D),

𝜶= The observed rotation,

Calculation

Concentration of the compound (c) = = 0.015 g/ml.

Observed rotation (𝜶) = -18° as rotation is counter-clockwise.

Length of the polarimeter = 20cm.

So, the specific rotation = = -60.

The specific rotation of the compound is -60.