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Poly Density Puzzle: a science brain teaser- white beads and blue beads "float" oddly separated beneath the surface of a clear liquid. If the contents are mixed by shaking the container, the white beads gather at the top and the blue sink to bottom! Adding to the mystery; after about 30 seconds the two layers of beads will have slowly moved back to the middle. What is your guess as to the physics behind this behavior? Follow the link in my profile for info on where to get this puzzle (and the physics that explains it) along with many other curiosities featured on @physicsfun #physicstoy #physicspuzzle #density #densitycolumn #immiscible #immiscibleliquids #bouyancy #archimedes #archimedesprinciple #saltingout #physics #science #scienceisawesome #polydensity A video posted by physicsfun (@physicsfun) on Sep 3, 2016 at 12:55pm PDT
Poly Density Puzzle: a science brain teaser- white beads and blue beads "float" oddly separated beneath the surface of a clear liquid. If the contents are mixed by shaking the container, the white beads gather at the top and the blue sink to bottom! Adding to the mystery; after about 30 seconds the two layers of beads will have slowly moved back to the middle. What is your guess as to the physics behind this behavior? Follow the link in my profile for info on where to get this puzzle (and the physics that explains it) along with many other curiosities featured on @physicsfun #physicstoy #physicspuzzle #density #densitycolumn #immiscible #immiscibleliquids #bouyancy #archimedes #archimedesprinciple #saltingout #physics #science #scienceisawesome #polydensity
A video posted by physicsfun (@physicsfun) on Sep 3, 2016 at 12:55pm PDT
Lesson Ideas
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When a 1 L bottle is shaken, the blue and white beads mix within the liquid as expected. However, when allowed to settle, the beads separate, white at the top and blue at the bottom. Shortly, the two separated colored beads slowly come together until they meet in the center of the liquid, white on top of blue. It is curious to see beads floating half way in a liquid. The mixing and separating can be observed over and over.
Please note: Rubbing alcohol is available in both 70% and 91%. Both are acceptable, but it is critical that you follow the correct procedure for the type of alcohol that you are using.
Preparation using 91% isopropanol:
Preparation using 70% isopropanol:
Explanation: Water and isopropanol are soluble in all proportions; they are miscible. Both the water molecules and the alcohol molecules have -OH groups that easily hydrogen bond to each other. The sodium chloride salt particles, Na1+ and Cl1-, however, preferentially bind with the water molecules forcing the alcohol molecules out of the water solution. This causes two layers to form: alcohol on top and the more dense water and salt layer on the bottom. Isopropanol and salt water are immiscible; they do not mix in all proportions. This 'salting out' technique is commonly used to remove organic molecules from an aqueous solution.
When the bottle is shaken, the two liquid layers momentarily mix, forming a pseudo homogenous mixture with a density between the two separate liquid densities. The white beads with a lesser density than this liquid mixture float on top and the blue beads with a greater density sink to the bottom. Then, as the aqueous salt layer separates from the alcohol, the blue beads rise in the bottom aqueous layer and the white beads sink in the top alcohol layer until they meet in the center. From lowest density to highest density the order is as follows: isopropanol, white beads, blue beads, and salt water. Because the beads float between the two liquids, the actual alcohol/salt water interface is difficult to observe, adding to the mystery. Order spontaneously forming from disorder is unexpected and gives the illusion of a violation of the Second Law of Thermodynamics.
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Students can use the Poly Density Kit in an investigation to describe and classify different kinds of materials by their observable properties.
Students can analyze data obtained from testing the Poly Density Kit to determine which materials have the properties that are best suited for an intended purpose.
Students can use the Poly Density Kit in an investigation to develop a model to describe that matter is made of particles too small to be seen.
Students can make observations and measurements of the different materials in the Poly Density Kit to identify materials based on their properties.
Students can use the Poly Density Kit in an investigation to develop models to describe the atomic composition of simple molecules and extended structures.
Students can use the Poly Density Kit in an investigation to predict properties of elements. Students can use the Periodic Table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.
Students can use the Poly Density Kit in an investigation to communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.
This Poly Density Kit is an awesome demonstration for density, solubility, miscibility and the salting effect. All students will be amazed by the actions the beads take. Due to the unexpected results in the bottle, secondary students have to use science to dissect an explanation for the layering. Great inquiry opportunities for all students. Some teachers never give away the secret.
Students can use the Poly Density Kit in an investigation of density. Shake up the bottle and let them sketch the various motions of the beads. For primary grades, a second bottle can be prepared with some food coloring added to the water solution, to bring a more concrete explanation. Secondary students may be able to use chemistry to decipher the paradox.
* NGSS is a registered trademark of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of, and do not endorse, this product.
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