chemical or physical change

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chemical or physical change

Postby artlab » Tue Jan 22, 2008 8:14 pm

Is the production of "Silly Putty" an example of a chemical or physical change? I've done reading on this...some sites seem to say that the production is the result of mixing/linking of the substances. On the "science-house.org" site, their directions list it as a chemical change. If it is a chemical change, does anyone know the equation? If I'm using polyvinyl acetate (white school glue) and starch....and/or using Borax/water mixture + glue--> silly putty. Is it really a new compound--or is it a mixture (colloid). Thanks. I hate giving out wrong information to my students. artlab
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Re: chemical or physical change

Postby davidkallman » Tue Jan 22, 2008 11:09 pm

Hi artlab,

From the silly putty frequently asked question page (http://www.sillyputty.com/silly_science ... e_faqs.htm), only the words mixed and mixture of "boric acid and silicone oil" are used. On the other hand, the science-house page that you mention (http://www.science-house.org/CO2/activi ... putty.html) clearly mentions that there are both physical and chemical changes.

So your instinct that a chemical change is involved appears to be correct. I suspect that the formula for the making of silly putty is contained in the patent for silly putty. Unfortunately, all the online databases with patent information appear to be for-profit sites. Maybe you know an attorney who has access to these sites or a fellow expert can help.
Cheers!

Dave
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Re: chemical or physical change

Postby artlab » Wed Jan 23, 2008 8:42 am

Thank you for taking the time to check into this. I'm not looking for the Silly Putty chemical reaction formula--but rather the chemical formula for the "recipe" on your site. 50/50 water & polyvinyl acetate + Borax solution--> "slime/putty". This would show whether or not a physical or chemical change has taken place, correct? My guess is that it is a chemical change--but the silly putty website is what made me question my assumptions. I have some VERY bright kids that ask great questions--and I prefer to give them correct answers--or at least good sources to find those answers!! :)
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Re: chemical or physical change

Postby ChrisG » Wed Jan 23, 2008 10:50 am

Hi,
This topic deals with a gray area between the "major" scientific disciplines. It may be too advanced for some 6-8th graders to consider that our definitions of "chemistry" and "physics" can overlap, but this project is a pretty good example. The description from the science house page is:
The borax is called a cross-linker. It chemically "ties together" the long strands of the polyvinyl acetate.

The term "cross-linker" does belong to chemistry, but doesn't that description about tying things together sound suspiciously physical? These sorts of gray areas fall into scientific disciplines like "physical chemistry" or, less commonly, "chemical physics".
the distinction between [chemical physics and physical chemistry] is vague, and workers often practice in each field during the course of their research.

http://en.wikipedia.org/wiki/Chemical_physics
So the bad news is that there is not a definitive answer to your question of whether this is physics or chemistry. Maybe the good news is that students will be intrigued to hear about this "gray area" of science and to consider what other gray areas might exist.

As far as a chemical formula, this is not a straightforward chemical reaction like "4Fe + 3O2 -> 2Fe2O3". It is typically represented with diagrams. For an example and for advanced discussion of this reaction, see pages 12-16 in http://dwb4.unl.edu/chem_source_pdf/POLY.pdf

You can find much more info by searching for "gluep".

Good luck!

Regards,
Chris
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Re: chemical or physical change

Postby davidkallman » Wed Jan 23, 2008 10:53 am

Hi artlab,

The detailed instructions for making silly putty are at:

http://www.science-house.org/CO2/activi ... putty.html

This webpage refers to a "polymer." Looking up "polymer" in the dictionary, we get:

a substance that has a molecular structure consisting chiefly or entirely of a large number of similar units bonded together, e.g., many synthetic organic materials used as plastics and resins.

It's clear from this definition that a chemical change has occurred, i.e., making a new molecular structure. Note: I'm not a chemist, just applying what appears to be true. Any chemists out there?
Cheers!

Dave
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Re: chemical or physical change

Postby artlab » Wed Jan 23, 2008 10:05 pm

Thanks everyone! I'm glad I'm not the only one who doesn't have a definitive answer. I have discussed "gray areas" with the students--actually part of why we "study" Silly Putty!! Is it an amorphous solid...or a slow-moving liquid? (They need to answer that and support their answer with the vocabulary and observations they have made--middle schoolers love to argue--so the idea of gray areas is perfect!!) In our text we are covering "solids, liquids, gases". Under solids--crystalline and amorphous solids are introduced. We grow Borax crystals and review a bit of earth science for the first...and then spend a few days on "the most famous amorphous solid"--Silly Putty. They actually produce 2 types--one using the directions on this site...and another using liquid starch and glue. The students then design labs to product test (elasticity, resiliance, viscosity). I love this site for explaining "variables" to them (which is how I ended up using this feature--I was revisiting the site to review your articles on that topic and noticed the "ask an expert" feature).

Up to this point, my lab experiences are very guided--this is the first time they will actually write their own from start to finish. It's a good preview of what they will do during their independent science projects later this year. (Which is when I really use your site!!) Our first step was to do some background research--in the form of a guided reading packet that I have compiled from the sillyputty.com site, and others. I challenge them to go online to that site so they can take the quiz and earn their "Masters in Silly Putty" certificate that they print out and bring in for extra credit.

Later, we do a small unit on materials science...and will re-visit this topic of polymers.

Thanks for all of your help....the kids thought it was "cool" that I had "asked an expert" about what we were doing!!
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Re: chemical or physical change

Postby ChrisG » Thu Jan 24, 2008 11:01 am

Thanks the update! It's great to hear that the kids are doing such interesting projects and that you all are making good use of this website. You sound like a wonderful teacher.

Regards,
Chris
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Re: chemical or physical change

Postby davidkallman » Thu Jan 24, 2008 12:56 pm

ChrisG wrote:Thanks the update! It's great to hear that the kids are doing such interesting projects and that you all are making good use of this website. You sound like a wonderful teacher.

Regards,
Chris

Hi artlab,

I second Chris's thoughts, particularly "You sound like a wonderful teacher." And It's wonderful to see what happens in real life, and how our bulletin board is used.

Your email makes my day!
Cheers!

Dave
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Re: chemical or physical change

Postby artlab » Wed Jan 30, 2008 8:05 pm

I have enjoyed this opportunity to post my question. Thanks for the compliments. We just finished our "Silly Putty" unit. After producing our putties...students designed labs to test for elasticity, viscosity, or resilience. They've collected the data...tomorrow the graphs are due...and the conclusions are due on Friday. Today I asked them to identify each sample as an amorphous solid or liquid...and defend their choices. They can't believe that real scientists would argue over such things! Many have taken the "Final Exam" on sillyputty.com and have printed out their "diplomas" from Silly Putty U--we have them hanging in the hallway. (Just in case you are wondering--from I've observed...the borax "putty" had the greatest elasticity (I know some stretched a wad of approx 13 g. over 700 cm! However...for resiliance--the real deal, Silly Putty brand, took the prize! The putty made from liquid starch and glue was most like Silly Putty--but it was more difficult to get to a good consistency. We are going to compare the data of all of the classes...and I'll create my own data table and graph of the class data) .

I'm sure you'll be hearing from me toward the end of the year, when we do "independent science projects". Your site will be posted as the best source of information on the "how to". Your explanations of "variables", etc., can't be beat!

This unit is a bit of a "tease" for what is to come. They will pick their favorite topic (I've had kids choose everything from snowboarding to stilts to beds...and of course, cosemetics and food) to investigate. They start out researching the history and science behind their favorite thing (the boys who did "beds" said their favorite thing was "sleeping")...and then end up developing experiements that correlate with some portion of their topic. Many end up doing more than one experiment. The grand finale, is they design activities to teach the "little kids" about the science of their favorite thing...and have an interactive science expo in the gym. Parents of the younger students in the community come out...and the seventh graders show off their wealth of knowledge and expertise. Many of our parents work in science fields...and are always impressed with the amount of background knowledge the students are able to communicate.

Students have used many of your ideas--and/or modified them. Last year I remember a boy learned that some hockey sticks were laminated (as are skateboards) and used your experiment that shows how lamination increases the strength. ("Are Laminates Stronger?") Kids who like guitars (especially electric guitars that use metal strings.) have used your experiemtent idea on corrosion. The "Viscosity of Motor Oil" is a good choice for anyone who chooses to do their project on their mini-bike (yes, we have had both mini bikes and mini race cars on display at our family science night!); your experiment on chemical lightening is a good help to the girls who like the topic of cosmetology. Of course, you have several good experiment ideas on food/baking related items, too. Even if they don't replicate the exact lab...they serve as FANTASTIC "exemplars".

All of the experiements are executed in class--so I get to see all of the excitement! I now know more than I would ever want to know about how skateboards and snowboards are made...and I've seen plenty of "insides" of basketballs, volleyballs, baseballs, and softballs. I've even seen sneakers cut in half (both by helpful parents and from displays at the local sneaker store). I've come to enjoy "materials science" more than I ever thought I would--and look forward to this part of the year. Despite the fact that the kids probably work harder during this part of the year than any other...it is the one thing that is repeatedly spoken about at 8th grade graduation as a memorable part of 7th grade. True pride, self-esteem, and sense of accomplishment comes from real authentic hard work. When students--no matter what their academic abilities are--are given the opportunity and motivation to investigate something of interest to them--it is AMAZING what they can accomplish!!

THANKS FOR YOUR CONTRIBUTION to their success.
Again, thanks!
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Re: chemical or physical change

Postby davidkallman » Thu Jan 31, 2008 9:43 am

Hi artlab,

Thanks so much for your post! It's great to hear about how our work is used; we'll have to see if any of your practice can be incorporated in our practice.

Selecting from the end of your message:
artlab wrote:When students--no matter what their academic abilities are--are given the opportunity and motivation to investigate something of interest to them--it is AMAZING what they can accomplish!!
Indeed, very well said.

artlab wrote: THANKS FOR YOUR CONTRIBUTION to their success.
You're welcome!
Cheers!

Dave
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Re: chemical or physical change

Postby ChrisG » Thu Jan 31, 2008 10:07 am

Artlab, Thanks for the update. :D
Chris
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