Sucrose Hydrolysis

facreInversion of Sucrose1
Purpose: The rate of reaction between sucrose and water catalyzed by hydrogen ion is followed
by measuring the angle of rotation of polarized light passing through the solution. Non-linear
curve fitting is used to extract the rate constants. Hydrochloric and monochloroacetic acid will be
used as the catalysts and the acids will be compared.
Introduction
The angle of rotation of polarized light passing through the solution is measured with a
polarimeter. The reaction is
C12H22O11 + H2O + H+
Sucrose

C16H12O6 + C6H12O6 + H+
Glucose

Fructose

Sucrose is dextrorotatory, but the resulting mixture of glucose and fructose is slightly
levorotatory, because the levorotatory fructose has a greater molar rotation than the
dextrorotatory glucose. As the sucrose is used up and the glucose-fructose mixture is formed, the
angle of rotation to the right (as the observer looks into the polarimeter tube) becomes less and
less, and finally the light is rotated to the left. The rotation is determined at the beginning (αο)
and at the end of the reaction (α∞), and the algebraic difference between these two readings is a
measure of the original concentration of the sucrose.
The reaction proceeds too slowly to be measured in pure water, but it is catalyzed by hydrogen
ions. The water is in such large excess that its concentration does not change appreciably, and the
reaction follows the equation for a first-order reaction, even though two different kinds of
molecules are involved in the reaction.
This same reaction in biological systems is catalyzed by an enzyme called invertase. The
hydrolysis of sucrose into single sugars is necessary before the sugars can be metabolized. In
humans, the invertase enzyme is found in saliva.
Theory
The rate law for the inversion of sucrose is in the form:
d[sucrose]
= k [sucrose]m [H2O]n [H+]p
dt

(1)

The concentration of water in this experiment is large, 55M, and essentially constant. We...