Polarimeter readings
We just finished a resolution lab. I combined my end product with a few other people with product similar to mine. Our prof graded our crystals and
the final liquid product collected with a simple distillation. We all had the same high grades. We knew the enantiomer collected rotated
plane-polarized light to the left and we knew its pure specific rotation. However, when placing the sample into the polarimeter I rotated the tube to
the left past 180, so that it essentially gave me a positive reading (the scale is split in half, 0 - ±180). Subtracting 180 from that gave me the
negative rotation and using that value we had very high optical purity.
Shouldn't I have been able to locate the point similar to the zero mark (where the viewfinder is half black/half light) at that negative rotation? I'm
wondering if it's just a random error on my part because we only read it once (we were in a hurry and sometimes I just don't think... Evidently so,
considering that rotating to the negative position would have taken five seconds) and I simply may have rotated the machine too quickly so that I
ended up on the opposite plane position. I guess my question is, if say I found the observed rotation of a product to be -70, if I rotated the
machine to +110 I would be able to view the same "zero" image, correct? Also, the product had a specific rotation smaller than 90, so it's
highly unlikely we collected a product with an absolute rotation greater than that.
We don't have class tomorrow and this is really bugging me. Thanks in advance for any help! (:
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