Experiment III: CHEMICAL ENGINEERING


Polymers and Microencapsulation

Objective
To introduce girls to polymers and some of their applications.

Materials
* Hardening solution (1.2% CaCl2); make 3-4 liters (no need to be very accurate) in liter glass bottles; fill bottles to liter line with distilled water. Add 13 grams of powdered CaCl2 . H2O; Stir with magnetic stir bar to dissolve. Remove stir bar, and close bottle securely with cap.

* Polymer solution (1.2% soldium alginate Kelco HV); This has to be started at least two days prior to trip. Make up stock 1.2% (w / volume) sodium alginate solution, then divide into individual bottles and add color or sand. For 400 mls: Put 400 ml of distilled water into a large beaker. Stir rapidly with magnetic stir bar. Weigh out 5 grams of alginate powder. Add slowly to the rapidly stirring water, trying to shake the powder into the vortex. Stir it over night until all dissolved. You may need to break up clumps with the spatula as it is stirring.

Color solutions: use the 100 ml glass bottles. Pour in about 100 ml of alginate then add about 6 drops of food color. Shake.

Sand solutions: Use the larger, 250 ml bottles. Pour in around 200 ml of alginate and add 14 grams of colored sand. You will have to shake it really well, and even so it will all settle to the bottom.

Alginate will depolymerize with time, so solutions should be kept refrigerated when not in use.

After the trip, collect all the syringes and needles and flush them out with water so that they can be used again.

Procedure

1) Starting Chat

Get them to sit in a circle if possible. Opening questions.
-Introduce yourself as a Chemical Engineer
-Do any of you have mothers, aunts, elder sisters, fathers, or anyone you know who is a Chemical Engineer?
-Do any of you know what a Chemical Engineer does?
Lead them through on their suggestions

Makes chemicals (link this to things they know, e.g. garbage bags)
Petrochemicals (compare what oil is like when it comes out of the ground to what it is like at the gas pumps) ENVIRONMENT (end of pipe solutions versus changing the process so no pollutant is made) Pharmaceutical/Medical (refer to what they will be doing in the lab) etc. etc.

Mostly problem solvers (lead into first activity).

2) Science Friction
Handout sheet.
-Divide up into pairs. Explain that this exercise will show them how an engineer thinks and tackles a problem. Say that one member must challenge the other. Hand out meter rules. Demonstrate what they have to do. Let them try several times, make sure each one has a go. Then lead them through the discovery process. Some sample questions: Does anyone notice what is happening (you are an engineer now, solving a problem in an engineering way observing is very important). Can anyone get both hands to move at once?

What is holding the ruler on your hand? What is the name of the force between your hand and the ruler? What determines how big this force is? (sand bags in trunk on icy day, big car better than small car on ice etc.)
What hand moves first? Does this relate to how much weight is on it?

-Conclusion
You have all become engineers in the making. You noticed a problem. You did experiments to confirm what you suspect. You made observations. You used science (physics) background to solve the problem. Friction is important to engineers, what do you get when there is a lot of friction?
HEAT

3) Microcapsules

Describe what a micrcapsule is.
Microcapsules in everyday life -
Do any of you get magazines with perfume samples inside that are just a piece of paper?
Explain.
Do any of you own a credit card? Explain carbonless paper.
Have any of you taken cold medicines that last all day? Explain tiny time pills.

To make microcapsules you need a polymer to make the tiny bag that holds your chemical. Does anyone know what a polymer is?

Polymerize the group. Explain polymers are long molecules made up of repeating molecules called monomers all joined together. Get them to be monomers moving around in solution. Make them move faster, you are heating them up. Get them to form at least two lines, holding hands (4-5 girls per chain). Now you have polymerized them. Get them to move again. Is it as easy? Explain viscous solutions. Show them the plain alginate solution. Show them alginate solid which the solution is made from. Now get them to reform lines, and use one or two girls to cross link between the stands. Now make them move. Now they have become a solid. Explain alginate is a long polymer with negative charges along it. Calcium ion has two positive charges so one charge grabs one polymer chain and the other grabs another. Show them CaCl2 solution. Pour some into a small bottle. Draw up some red alginate into a syringe. Drop the alginate drop by drop into the solution to form capsules. Show them the sand, explain to them a needle would plug up. Let them loose. Suggest they use two bottles one for the sand and the other for the color.
Encourage them to experiment --- Can anyone make spaghetti? etc. Make up four bottles each with the different colors in. Towards end try to get their attention to explain "Diffusion", explain that the blue color of a very big molecule and the others are smaller (yellow fastest out, must be the smallest). Hence design to fit your molecule.


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