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# matenal 111 (m: Lmumuun . silica gel absorbs the water at the solve when placed in a beaker of L00 X 102 g of polymer. Since thet problem, you do not...

matenal 111 (m: Lmumuun .. .,-.. _ _. silica gel absorbs the water at the solve when placed in a beaker of
L00 X 102 g of polymer. Since thet
problem, you do not have to use mo
you can use mass rates. abov e 1' ate. water. Assume that Y‘
e is no chemical stoichmmﬁﬁ
[at rates in order to solve

{a} You start simple with your modeling predictions. You assume that the
polymer does not degrade [i.e., it undergoes no chemical transformations
to another polymer or smaller monomer units}. Rather, you assume that
the dissolution rate of the polymer is proportional to a constant, is, and
the Surface area of the polymer, A. This can be modeled as follows: dissolution rate = H;
where: S
k =
2hr-ctn A =1ocm2 Using this predictive model, how long will it take for the 1.00 X 102 g
polymer slah to dissolve completely in water? {b} Realizing that your ﬁrst aswmption is too simple, you try to model the
dissolution rate as a function of the square root of time as follows: 2 dissolution rate = livid” where:
_ 3
I k _ Z‘Ol'lr'cmz
Cl'l'l2
An = 10.0 hr” Using this predictive model, how long will it take for the 1.00 X 102 g
polymer slab to dissolve compliately in water? it] After talking with a colleague, you realize that in addition to dissolving, the
polymer also degrades to a monomer. Expecting that taking account of this
might signiﬁcantly improve your model, you investigate further. You con—
duct a series of experiments to determine the polymer’s degradation rate.
During the first hour the rate increases linearly to a value of 10.0 glhr, then
plateaus and is a constant at 10.0 giht, as shown in Figure 3.39. Using the mode] for the dissolution rate from part {a}, you combine the
dissolution and degradation terms into one model. For this experiment, you
begin the trial with a 1.00 X 1033 polymer slab, yet stop the experiment ; when the mass of the polymer is 20.0 3. Using this model, how long will it take for the polymer to reduce in mass from 1.00 x 102 g to 20.0 g in water?
Biodmndnlilr anthem-ir- mnh-mJA&quot; _..- .a _. l &gt; u . . J .
.3;
up, Problems p—I
U! 0 1 2 3 4 5
'Iime(hr) Figure 3.39
into monomers in water. 187

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