how to calculate specific observed rotation?
It will depend on whether it is a pure liquid or a solution. If a pure liquid
[Alpha]T,lamdba =
measured rotation/(path length x density)
for a solution
[Alpha]T,lamdba =
measured rotation/(path length x concentration)
To calculate the specific observed rotation of a substance, you will need the following information:
1. Length of the sample: Measure the length of the sample in decimeters (dm). This is the distance the light travels through the sample.
2. Concentration of the sample: Determine the concentration of the substance in grams per milliliter (g/mL). This is the amount of the substance dissolved in a given volume of solvent.
3. Observed rotation: Measure the observed rotation (in degrees) using a polarimeter or similar instrument. This is the angle by which the plane of polarized light is rotated when passing through the sample.
The specific observed rotation (α) is then calculated using the following formula:
α = (Observed rotation in degrees) / (Length of the sample in dm) / (Concentration in g/mL)
For example, let's say you have a sample with an observed rotation of 15 degrees, a length of 2 dm, and a concentration of 0.5 g/mL. Using the formula, the specific observed rotation would be:
α = 15 degrees / 2 dm / 0.5 g/mL = 15 / 2 / 0.5 = 15 / 1 = 15
So the specific observed rotation for this example is 15 degrees.
Remember to use consistent units throughout the calculations and double-check your measurements for accuracy.