The optical rotation of a sample composed of only (S)-2-bromobutane is determine

Question

The optical rotation of a sample composed of only (S)-2-bromobutane is determined. [alpha]abs = -0.27°. If the cell path length was 1.2 dm and the concentration of (S)-2-bromobutane in the sample was 1.3 g/mL, what is the specific observed rotation?

A. 0.23 degrees

B. -6.5 degrees

C. -0.17 degrees

D. 14.2 degrees

E. -47.1 degrees

A sample of pure (d)-borneol is found to produce an [alpha]abs = 18.4°. What must be the concentration if [alpha]D = 22.7 mL/g·dm assuming a 1.3 dm pathlength?

A. 23.3 g/mL

B. 2.33 g/mL

C. 0.52 g/mL

D. 0.62 g/mL

E. 0.23 g/mL

PLEASE SHOW WORK OR EQUATION

Explanation / Answer

1. [alpha] = alphaobs / (l x C)

[alpha] = -0.27/(1.2x1.3) = -0.17 degrees

Ans : C

2. [alpha] = alphaobs / (l x C)

C = 18.4 / (22.7 x 1.3)

C = 0.62 g/mL

Ans : D

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