This is my report on our activity about the Silica Gel. Silica Gel is such a wonderful material used as a drying agent since time and a great tool in preserving other things such as electronics, shoes, and food. [This activity was conducted (November 10,2016) in Mindanao State University - Iligan Institute of Technology (MSU-IIT), in the Material Science Laboratory of the Physics Department] The goal of uploading this file is to guide and aid in understanding the nature of the Silica Gel. Furthermore, it is a personal remembrance because I liked the mechanism of Silica Gel. Reminder: To make things valid, please make a research on your own. What was written here might be incomplete, contradicting, or invalid. So please don't copy paste everything especially on the results because We only used 2 dessicant bulks with this. Statistically, two (2) is not enough for a conclusion. Have a nice day and enjoy!

1. Maria Jane S. Poncardas November 16, 2016
Activity 5 (PHYS 210 BBB, TTh, 3-6PM) Group 4
ADSORPTION WITH SILICA GEL
Adsorption is a surface phenomenon in essence. It means that there is a distribution of a
substance at the surface of the bulk. This substance is called the adsorbate molecules which are
captured in the pores of the adsorbent due to the Van Der Waals and electrostatic force between
the adsorbate and the adsorbent.
When the adsorbate molecules interact with the adsorbent, its molecular distances inside
the adsorbent’s pores are much shorter, hence it appears to have a liquid-like phase. Thus, a good
adsorbent must have reasonably large surface area or micropore volume, and it must have
relatively large pore (macropore and micropore) network for the transport of molecules to the
interior. Macropore functions as diffusion paths of adsorbate molecules from outside the granule
to the micropores in fine powders and crystal absorbents.
The different mechanisms of adsorption are chemical adsorption and physical adsorption.
When there is a weak Van Der Waals forces of attraction on adsorbate and adsorbent, the process
is called the physical adsorption. This process can be reversed using heat or pressure. Heat is
released due to the change in energy level of the adsorbate molecules between gaseous and
adsorbed phases, thus it is a form of an exothermic process. On the other hand, when the process
is not a complete reversible as physical adsorption, it is called the chemical adsorption. It is when
the attraction force is given by chemical reactions resulting in chemical bond formation.
As per processes, some adsorbents are also “hydrophilic” due to certain affinity with water
and the example for this is the silica gel, SiO2, also used as desiccant (drying agent). It is usually
included when we purchase new shoes or electronics or food to limit the growth of the mold and
reduce spoilage. It can adsorb about 40% of its weight in moisture and can take the relative
humidity in a closed container. Different types of silica gel is based on its chemical composition:
1.White Silica Gel has SiO2 + H2O, and 2.Blue Silica Gel has SiO2 + H2O + CoCl2. The cobalt
chloride attached to the blue silica gel is the reason of its initial color. It is usually used to indicate
the changes of its color in response to humidity. As humidity increases, cobalt chloride changes
from blue to pink.
In this activity, we will generate a time-series measurement of a single blue silica gel mass
which humidity is considered. Also, what happens to a single silica gel if it was placed in a
container?
References:
1. Cevallos, O.R.F (2012). Adsorption Characteristics of Water and Silica Gel System for
Desalination Cycle (Unpublished Master thesis). King Abdullah University of Science and
Technology, Thuwal, Kingdom of Saudi Arabia.
2. HowStuffWorks. (2000, April 1). What is silica gel and why do I find little packets of it in
everything I buy? Retrieved November 17, 2016, from
http://science.howstuffworks.com/innovation/science-questions/question206.htm

2. 3. Welcome to silica gel. Retrieved November 21, 2016, from http://www.silicagel.in/about-
silicagel.html
4. Council, A. C. (2005). Cobalt chloride: Colorful moisture detector. Retrieved November
21, 2016, from https://chlorine.americanchemistry.com/Science-Center/Chlorine-
Compound-of-the-Month-Library/Cobalt-Chloride-Colorful-Moisture-Detector/
Materials needed:
Two (2) Desiccants of same diameter
Closed container
Analytical Balance
Stopwatch
Procedure:
1. Take images of two (2) desiccants under the poroscope to compare the diameter. Use
magnifications: 0.5x, 0.8x, 1.0x and 1.5x.
2. One desiccant will be measured in the analytical balance and the other will be placed in a
closed container at the same instance.
a. For the desiccant that will be assigned in the analytical balance, record its mass
every minute from time t=0 to t=120 minutes. [Important: Analytical balance
should be opened on one side]
b. For the desiccant placed in a closed container, observe the changes in its
appearance.
3. Take another set of images to compare the appearance initially and after the experiment.
Figure 1 Analytical balance and blue silica gel (desiccant)

3. Results:
I. Initial and final appearances of the desiccant
The images shown are of two Silica gel desiccants, of varying magnifications (0.5x, 0.8x,
1.0x, 1.5x). Each magnification is subdivided into four parts, the top-left is the initial condition of
a desiccant stored in a container (in our case, we used Petri dish). The bottom-left image is of the
weighed desiccant under the analytical balance. The top- and bottom- right images are the
appearances of the desiccants after two hours (120 minutes).
Initially, the diameter of the stored desiccant is at 430 pixels (in accordance to the 0.5x
magnification) approximately equivalent to 1.002mm [cf: 1090 px ≈ 1/10 in]. The final diameter
is at 428 pixels equivalent to 0.9973 mm.
Furthermore, the initial diameter of the weighed desiccant has 1.0206 mm (438px) and
final diameter of 1.0043 mm (431px), which basically decreased in size.
A B
C D
Figure 2 Initial and final appearances of stored and weighed desiccant under magnification: A.0.5x, B.
0.8x, C. 1.0x, D. 1.5x

4. II. Mass of the desiccant (Room temperature at 20.8 ̊C initial humidity 50%)
We have measured the diameter of the single desiccant which appears to have decreased.
However, its mass is increasing periodically overtime. Initially, the mass is 0.0163g. At 0-18th
minute in the analytical balance, there was an abrupt increase of its mass. The appearance slowly
changed from blue to pink (pink was less likely observed). Then, at 20-120 minutes, it still
experiences an increase in mass (with a slope increase of 2.40) although it was expected to have
saturated within this time frame. Its color transition is from pink to transparent. In theory, it can
adsorb about 40% (max) of its weight in moisture, for this case the 40% increase in mass was
observed at approximately 87th
-minute mark (See Appendix). Hypothetically, if the mass was yet
to be observed after 120 minutes, saturation happens.
0 20 40 60 80 100 120
0.016
0.017
0.018
0.019
0.020
0.021
0.022
0.023
Mass(g)
Time (mins)
Mass of the Desiccant
Linear Fit
Model Line
Equation y = A + B*x
Reduced
Chi-Sqr
3.70512
E-7
Adj. R-Squa 0.57445
Value Standard Er
B
A 0.01896 1.54505E-4
B 2.39891 2.04697E-6
Figure 3 Time-series measurement of the mass of the desiccant for 120 minutes

5. Questions and analyses:
1. Why we should use Silica Gel as desiccant?
It is recyclable by heating so it will go back to its initial appearance without destroying
the bulk. It also has the highest H2O capacity at 25 ̊C.
Figure 4 Water (H2O) capacity of different desiccants at 25 ̊C (Image taken from Inc, T.P. (2007)]
2. At what point saturation occurs?
Based on our measurement of the mass of the desiccant, saturation was not yet observed.
However, the maximum adsorption of the desiccant starts at approximately 87th
-minute.
3. What is the maximum absorption of the Desiccant?
0.0227 grams (or 0.0064g adsorbed), which is approximately 39.26% increase from its
initial mass.
4. What are the colors before and after 120 minutes?
For weighed desiccant: initially it has a blue color, then after 120 minutes, it changed
to transparent.
For stored desiccant: initially it has a blue color, then after 120 minutes, it changed to
pink.
5. What is the reason of the color change?
Cobalt chloride crystals attached to the blue Silica Gel is the reason as to why the blue
color changed to pink or transparent. It is usually used to indicate the changes of its
color in response to humidity. As humidity increases, cobalt chloride changes from
blue to pink.

6. 6. Is it physically or chemically adsorbed?
- We say that it has a physical adsorption phenomenon during which the adsorbate
molecules only surrounded the surface and pores of the bulk desiccant, the reason
why the mass of the silica gel increased in time.
- It is chemically adsorbed when the color changes occurred, that is, on the cobalt
chloride. See the following reaction:
7. Why do we need to combine cobalt chloride with Silica gel when the cobalt chloride and
silica gel can stand separately?
For a silica gel alone, it can adsorb water molecules readily, but how can we identify if
it indeed adsorbed water? Or how can we indicate if it reaches the maximum adsorption?
This is the beauty of the blue silica gel, it can adsorb water molecules, and at the same
time, it can indicate the maximum capacity of the desiccant to adsorb moisture (when it
becomes transparent, for the case of the blue silica gel).
References:
1. Inc, T. P. (2007). T E C H N I C A L N O T E S PELCO ® facts and information about
indicating Desiccant. Retrieved on November 20, 2016. Retrieved from
https://www.tedpella.com/technote_html/desiccant.pdf.
2. Council, A. C. (2005). Cobalt chloride: Colorful moisture detector. Retrieved November
21, 2016, from https://chlorine.americanchemistry.com/Science-Center/Chlorine-
Compound-of-the-Month-Library/Cobalt-Chloride-Colorful-Moisture-Detector/

7. APPENDIX
Initial Mass of the Desiccant: 0.0163g
Time
(min)
Mass
(g)
Time
(min)
Mass
(g)
Time
(min)
Mass
(g)
Time
(min)
Mass
(g)
1 0.0171 31 0.0194 61 0.0208 91 0.0215
2 0.0175 32 0.0198 62 0.021 92 0.0211
3 0.018 33 0.0195 63 0.021 93 0.022
4 0.0183 34 0.0198 64 0.021 94 0.022
5 0.0179 35 0.0195 65 0.0206 95 0.0218
6 0.0183 36 0.0194 66 0.0209 96 0.0217
7 0.0183 37 0.0198 67 0.0212 97 0.0219
8 0.0188 38 0.0199 68 0.0213 98 0.0212
9 0.0192 39 0.02 69 0.021 99 0.0216
10 0.0189 40 0.0197 70 0.0216 100 0.0212
11 0.019 41 0.0191 71 0.0214 101 0.0209
12 0.0194 42 0.02 72 0.0218 102 0.021
13 0.0193 43 0.0197 73 0.021 103 0.0212
14 0.0188 44 0.0206 74 0.0215 104 0.0209
15 0.0188 45 0.02 75 0.0214 105 0.0215
16 0.019 46 0.0196 76 0.021 106 0.0205
17 0.019 47 0.0195 77 0.0211 107 0.0215
18 0.0194 48 0.0199 78 0.0209 108 0.0211
19 0.0183 49 0.0194 79 0.0211 109 0.0216
20 0.0191 50 0.0203 80 0.0209 110 0.0212
21 0.0195 51 0.0202 81 0.0206 111 0.0211
22 0.0186 52 0.0201 82 0.0207 112 0.0208
23 0.0195 53 0.0207 83 0.0211 113 0.0212
24 0.0193 54 0.0201 84 0.0218 114 0.02
25 0.0194 55 0.02 85 0.0215 115 0.0209
26 0.0194 56 0.0208 86 0.022 116 0.0205
27 0.0182 57 0.0207 87 0.0227 117 0.0204
28 0.0192 58 0.0205 88 0.0218 118 0.0208
29 0.0192 59 0.0209 89 0.0222 119 0.0208
30 0.0195 60 0.0205 90 0.0222 120 0.0219
Table 1. Time-series measurement of mass of the desiccant for 120 minutes (measured every
minute)