Question

The specific rotation, [α]_D, for (-)-2-butanol is +14. What is the observed rotation for a solution of 3.3 g of (-)-2-butanol in 10 mL of water in a sample tube having a pathlength of 10 cm?

degrees .

The observed rotation of a solution of 1.7 g of a compound in 10 mL of water is +5.8 degrees. If the pathlength is 10 cm, what is the specific rotation of the compound?

degrees

Answer 1

The specific rotation, [α]_D, for (-)-2-butanol is +14. What is the observed rotation for a solution of 3.3 g of(-)-2-butanol in 10 mL of water in a sample tube having a pathlength of 10 cm?

[A]D = Aobserved / (C*l); where C = concentration, l = 10 cm = 1dm

C = mass/volume = 3.3/10 = 0.33 g/mL

+14 = Aobserved / ( 0.33 * 1)

Aobs = 14*(0.33*1)

Aobs = 4.62

B)

C = mass/V = 1.7/10 = 0.17

Abos = 5.8

D = 10 cm = 1 dm

[A]D = Aobserved / (C*l); where C = concentration, l = 10 cm = 1dm

[A]D = Aobserved / (C*l);

[A]D = 5.8 / (0.17*1) = 34.11