Question

Polarimeters are so sensitive that they can measure

rotationsto the thousandth of a degree, an important advantage when
onlysmall amounts of a sample are available. For example, when
7.00mgof ecdysone, an insect hormone that controls molting in
thesilkworm moth, was dissolved in 1.00 ml of choloroform in a
cellwith a 2.00 cm path length, an observed rotation
of+0.087o was found. Calculate [a]d
forecdysone.

Answer 1

`[\alpha ]=62.1`

Step-by-step explanation:

The equation to calculate the specific rotation (
`[\alpha ]`) of a substance is:

`[\alpha ]=(\alpha)/(c*l)`

Where:

• 
  `\alpha` is the optical rotation
• 
  `c` is the concentration in g/ml
• 
  `l` is the path length in dm

In this case:

`l=2 cm=0.2dm`

`c=(0.007 g)/(ml)`

`\alpha=0.087`

The specific rotation:

`[\alpha ]=(0.087)/(0.007*0.2)=62.1`