Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

390 a-ACBTOBKOMOGLUCOSB •
intersection of the curve with the Y-axis, and so the rotation at zero
time; if one-third of this initial dextro-rotation is plotted (as final laevorotation)
below the rotation of 0° on the Y-axis, the time when this
ultimate rotation is approximately reached can be ascertained graphically.
We next test whether the half-value time is constant, i.e. whether
the moments at which one-half, one-quarter, one-eighth of the total
change in rotation have still to occur and similar fractions of the sugar
remain unhydrolysed (as indicated by the curve) are really separated
by equal intervals of time. Since the diminution in the rotation is
directly proportional to the amount of sugar inverted, this diminution
is at once a measure of the reaction velocity.
The observed changes of rotation and the corresponding times
should be substituted in the following equation for unimolecular reactions,
and the constant K should be calculated.
log (at - a) - log (a2 - a)
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