Question

Ecdysone is an insect hormone that controls molting. In a polarimetric experiment, 70.00 mg of ecdysone was dissolved in 10.00 mL of chloroform, and the solution was placed in a 2.0 cm path-length cell. The optical rotation was measured at 20 °C using the yellow sodium D line near 589 nm wavelength. If the rotation observed was of +0.087°, calculate the 20Davalue for ecdysone.

Answer 1

The specific rotation is 62 °.mL . dm⁻¹ g⁻¹.

Step-by-step explanation:

In a polarimetric experiment, we can calculate the specific rotation (
`[\alpha ]_(D)^(20)`) for ecdysone using the following expression:

`[\alpha ]_(D)^(20) =(\alpha )/(l * c )`

where,

α is the angle of rotation

l is the path length in decimeters (2.0 cm = 0.20 dm)

c is the concentration in g/mL

Concentration is:

`c=(massof solute)/(volumeof solution) =(70.00 * 10^(-3)g  )/(10.00mL) =7.000 * 10^(-3)g/L`

Then,

`[\alpha ]_(D)^(20) =(\alpha )/(l * c )=(0.087\textdegree )/(0.20dm * 7.000 * 10^(-3)g/mL ) =62 \textdegree .mL .dm^(-1). g^(-1)`