Science Buddies: "Ask an Expert"

Hi so i have 2 questions and one of them is kinda not exactly super related but it is?

Question 1:
I am interested in making the biodegradable fabric according to the procedure given in the experiment "make sustainable fabrics from seaweed". However, instead of testing physical properties of the jelly matrix, like test of durability as seen in the experiment given, I would like to test the chemical-ish properties like the solubility of the fabric in acids.
I could take like different concentrations or volumes of pH of an acid and leave the fabric in it for a certain amount of days. Then, I would check maybe how much of the fabric has dissolved?
So could you provide some suggestions on how I would check the solubility of the jelly matrix in the acid maybe if you have any ideas, idk like back titration? I know its like not super related but suggestion would be nice

Question 2:
What exactly is the significance of the calcium chloride and why is it important to be only sprayed?
like is it fine if i don't? and why can't i just add a sodium chloride solution to the mixture beforehand.

Thank you so much.


[Administrator note -- project directions: https://www.sciencebuddies.org/science- ... biofabrics ]

Hello!

These are great questions.

For your first question:

One chemical property test that is involved in the Science Buddies project that you're completing is a pH test. I recommend doing this test. Other tests for chemical properties of textiles that are often performed are often for the different types of (potentially harmful to human health and the environment) dyes that are present in textiles. These dyes would likely not be present in the seaweed textiles that you will make during this experiment, so these tests would not tell the best story about the results of your project.

One chemical test that may be relevant for seaweed-derived textiles for your project would be a heavy metal test. Seaweed may absorb heavy metals present in the water they grow in, which can have negative human health effects if these heavy metals are present in large quantities in the fabrics. One way you can test for the presence of heavy metals is by purchasing heavy metal testing strips that are relatively cheap to buy online and can be used to test for heavy metals in water. You can dip one of these test strips in the alginate mixture before pouring the mixture into the mold and see what you find. The test usually involves dipping the test strip in a solution, and matching the colors you see on the strip to a guide included with the kit which will tell you which (if any) metals are present.

For your second question:

The significance of the calcium chloride (chemical formula CaCl) is that when the sodium alginate comes in contact with the CaCl, it becomes a gel-like substance. The sodium alginate will not do this on its own, because the chemical formula (which determines the properties) for the gel-like substance is C12H14CaO12. Notice that this formula involves calcium (Ca).

So, the reaction you see here in Equation 1 (I know this is not the link to your exact project, but this Science Buddies project below provides some good information related to your project!) is the reaction that is happening between the sodium alginate and the calcium chloride to produce the gel-like substance: https://www.sciencebuddies.org/science- ... rification. Since the sodium from the sodium alginate is replaced by the calcium, the sodium alginate undergoes the "spherification" process and becomes gel-like. So, calcium chloride is needed to give a calcium atom to the alginate to give the alginate gel-like properties that it doesn't have when it's bonded to sodium.

It's important to spray the calcium chloride solution so that the sodium alginate does not form a gel-like substance that ends up floating in the calcium chloride solution. If there is too much calcium chloride solution, all of the sodium alginate will react, and the calcium chloride solution will be left over. So, the gel-like material that has formed from the sodium alginate will end up floating around in the mold full of solution instead of filling the mold itself as a gel-like substance.

Hope this helps and let us know if you have any further questions!