Science Activity
#8 - Silica Gel
All experiments must be done in the presence of a parent or teacher.
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Ideas
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Key Words
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Materials
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Procedure
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Observations
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Summary
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Questions
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WWW Links

Ideas to be Developed

Small packets that are printed

'SILICA GEL DO NOT EAT'

are often found in packing and shipping containers of films, cameras, binoculars, computer equipment, leather shoes, clothing, foods, medicines, and tools.

When the equipment is removed from the shipping boxes, these packets are often thrown away. What is in the content of these packets and what are they used for?

Silica gel packets are dessicants. These packets adsorb moisture and prevent damage to stored valuables and supplies.

Silica gel is silicon dioxide, SiO2, like sand on the beach. Inside each small silica gel granule is a network of inter-connecting microscopic pores, which attract and hold moisture by a phenomena known as adsorption. Silica gel is packaged in a fibrous material that is capable of withstanding normal handling and be able to breathe. This means that water molecules can pass through the material and be adsorbed by the silica gel.

Ready to use silica gel is blue in colour. When the silica gel has soaked up a lot of moisture, the silica gel turns to pink. Once the silica gel turns pink it cannot adsorb any more moisture. It needs to be regenerated. This can be accomplished by heating it in an oven. The heat expels the moisture, the silica gel turns blue and becomes reusable.



Ready to use silica gel


Silica gel turns pink once it has soaked up moisture.

Besides keeping moisture away from shoes and hard drives, silica gel is also used in drying flowers. We will be using silica gel to dry some fresh flower petals.


Key Words
Adsorption - The capability of substances to attract to their surfaces molecules of gases, water or solutions with which they are in contact.
Dessicant - Something that absorbs moisture from the atmosphere.

Silica Gel - A material that is capable to adsorb moisture.

Materials Required
Ask your parents to help you look for silica gel packets that you may have around your home (Hint: good places to look for are shoe boxes, boxes that store computer, camera, binocular). Bring them in to class for classroom discussion.
On the day of the lab bring in small samples of freshly picked flower petals from home.
Bring in a small container with a snap or screw lid.
Examples of suitable small containers

Suitable containers

Procedure

Determine the Moisture Content of Silica Gel:

1. Follow the teacher's instruction on the operation of a triple-beam balance.
2. Your teacher will give you a sample of silica gel wrapped in aluminum foil.

3. Using the triple-beam balance, determine and record the mass of the sample of silica gel and aluminum foil before heating. Enter the mass in the space provided in the Data section below. This is the mass of silica gel and aluminum foil (before heating). - Data Item #1
a package of silica gel
4. Crack open the middle section of the aluminum foil and record your observations of the silica gel.

5. With your teacher's assistance, place the opened package on the hot plate and let it heat for 10 to 15 minutes. Your teacher will occasionally mix the silica gel around with a spatula. Record your observations of what is happenening. BE CAREFUL NOT TO TOUCH THE HOT PLATE OR THE ALUMINUM FOIL, IT IS HOT!

6. Once the content of the package changed colour completely, your teacher will assist you in removing the package of silica gel from the hot plate to cool (about 10 to 15 minutes).

7. Using the triple-beam balance, determine and record the mass of the sample of silica gel and aluminum foil after heating. Enter the mass in the space provided in the Data section below. This is the mass of silica gel and aluminum foil (after heating). - Data Item #2

silica gel package on hot plate

8. Follow instructions # 9, 10, and 11 below and use the heated silica gel to dry some flowers.

Drying Flowers with Silica Gel:
9. Transfer half of the silica gel to the container that you brought from home.
10. Lay some flower petals on the silica gel.
11. Transfer the remaining silica gel to the jar. Replace the lid and let sit for overnight.
If you have left over silica gel, return it to your teacher. DO NOT THROW AWAY ANY SILICA GEL, IT IS REUSEABLE.
12. Next day, make observation of the flower petals and the silica gel.
13. Return all the silica gel to your teacher.

14. Roll your aluminum foil into a ball and determine the mass of the aluminum foil. Record the mass of aluminum foil. - Data Item #3. You may discard the aluminum foil after determining its mass.

15. Determine the percentage of moisture by mass that silica gel is able to adsorb.


Observations

Your prediction:

100 grams of silica gel is able to adsorb:

< 10 grams of moisture 10 - 30 grams of moisture 30 - 50 grams of moisture
50 - 80 grams of moisture 80 - 100 grams of moisture > 100 grams of moisture

Silica gel BEFORE heating. Sketch and make observation of the silica gel.
Is this silica gel ready to use or is it full of moisture?

Silica gel AFTER heating. Sketch and make observation of the silica gel.
Is this silica gel ready to use or is it full of moisture?

Silica gel overnight. Sketch and make observation on the silica gel and the petals.
Has your silica gel changed colour? Do you think the silica gel is still good to use or does it need to be regenerated?


Data
1. Mass of silica gel and aluminum foil (before heating) ....................... _______________ g.
2. Mass of silica gel and aluminum foil (after heating) .......................... _______________ g.
3. Mass of aluminum foil .......................................................................... _______________ g.
4. Mass of silica gel before heating (# 1 - # 3) .................................... _______________ g.
5. Mass of silica gel after heating(# 2 - # 3) ........................................ _______________ g.
6. Mass of water driven off (# 4 - # 5) ................................................. _______________ g.

Determine the percentage of moisture by mass that silica gel is able to adsorb.

% moisture by mass = mass of water driven off (Data Item #6)* 100
mass of silica gel after heating (Data Item #5)

 

 

 

 

 

 


Summary

Summarize your findings and comment on your prediction and the outcome of this experiment.

Questions


1. What kind of damage can occur if silica gel packets are not included in the shipping of electronic goods, foods and medicine?

 

 

 

2. How long has Silica Gel been developed as a dessicant?

 

 

3. What is in the Silica Gel that causes it to change colour?






WWW Links
1.Characteristics, safety and use of silica
2.Silica gel - Frequently Asked Questions
3.Silica gel - MSDS

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Ideas
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Key Words
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Materials
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Procedure
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Observations
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Summary
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Questions
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WWW Links

Howard Debeck Elementary School
8600 Ash Street Richmond, B.C. V6Y 1S2
Phone: 604-668-6281 - Fax: 604-668-6004


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