# Homework Help: Calculating the Optical Rotation Value

1. Nov 29, 2012

### Interception

1. The problem statement, all variables and given/known data So the problem states that we have a (+) enantiomer of a coumpund with an optical rotation of 50*. If a pure sample containes 42% of the (+) enantiomer and 58% of the (-) enantioimer, what is the optical rotation value. (By * i mean degrees)

2. Relevant equations I'm not sure which equation would apply to this situation. It's a small school, and our proffesor hardly went over this subject. We'd done a few problems, but none where like this.

3. The attempt at a solution I know that it will be a negative value since the the (-) enantiomer outnumbers the (+). I didn't know how to approach the problem, so I took 58%-the 42% to see how much of the (-) will contribute to the rotations since the 42% of the (+) enantiomer will counteract 42% of the (-) enantiomer. I got -16. I took this mean that 16% of the (-) enantiomer would be optically active, and 16% of 50 is 8, or in this case -8* of optical rotation. The negative value makes sense, and the fact that it's not a large number. Does this look right?

2. Nov 30, 2012

### Staff: Mentor

Looks OK to me.