Reactivity of Oxygen Bleaches: Crystalline Particles versus
Granules
The students then applied their previous attained knowledge
on the chemical composition and structure of the SPC granules
toward the reactivities and reaction mechanisms of oxygen
bleaches. The first topic involved a comparison of the bleaching
reactivities of dissolved SPC crystalline particles and granules in
water (Figure 1, Step 2). Although the students initially
presumed that both solutions had comparable bleaching
activities, they observed that only the solution of SPC granules
exhibited an oxidation activity after a set of period of time
(Figure 1, Step 2, E2). This is because SPC crystalline particles
exhibit a higher dissolution rate, which subsequently leads to a
higher rate of H2O2 decomposition. This result taught the
students that the oxidation of the organic dyes and the
decomposition of H2O2 were both competing reactions. This
fact was also later reinforced by the instructor (Figure 1, Step 2,
I2). Students also learned that the outer surface layer of SPC
granules protected the internal SPC crystalline particles from
atmospheric moisture (Figure 1, Step 2, L2), which allowed the
particles to have a longer in-house storage. At this point, the
instructor explained that the outer surface layer protected the
internal SPC crystalline particles by acting a barrier to prevent
the diffusion of water vapor into the granules. This is observed
because the absorption of water vapor by Na2CO3(s) causes a
hydration reaction that convers this chemical component to
Na2CO3•H2O(s).
At the end of the session, the instructor introduced the
chemical concepts for the formation of hydroxyl radicals
(Figure 1, Step 2, I2), which aids in the decomposition of
H2O2.22−26 The students also gained an understanding of the
role of the generated hydroxyl radicals in the bleaching process,
which allowed them to apply this gained knowledge toward the
following exercise.