Question

What observed rotation is expected when a 1.36 M solution of (R)-2-butanol is mixed with an equal volume of a 0.680 M solution of racemic 2-butanol, and the resulting solution is analyzed in a sample container that is 1 dm long? The specific rotation of (R)-2-butanol is –13.9 degrees mL g–1 dm–1.

Answer 1

The specific rotation of (R)-2-butanol = –13.9 degrees mL g–1 dm–1.

concentration = 0.680 M = 0.680 mol / L

                     = 0.680 x 74.12 / 1000

                     = 0.0504 g / mL

length = 1 dm

Observed rotation = specific rotation x concentration x length

                          = - 13.9 x 0.0504 x 1

Observed rotation = - 0.701 degrees