P2P Blue Licks State Resort Park 14 April 2009 Learning targets I can observe that when materials change, their mass does not change. I can show that the mass of something is the sum of the masses of its parts. I can show that volume is often not conserved when materials are mixed. I can see that volume may not be conserved because particles of one material may fit into the spaces between larger particles in another material. I can observe some properties changing under different conditions I can observe that some kinds of changes that can occur to materials are characteristic changes, and can be used to identify the type of material. Mixing objects You will be asked to determine the mass and volume of several objects. To determine the mass of something in this activity, first determine the mass of an empty graduated cylinder, place the material to measure in the cylinder, then again measure the mass, and subtract the two for the mass of the object itself. a) Use a 100 mL graduated cylinder to measure as close as possible 50 mL of marbles. Determine their mass and gently place into a 400 mL beaker. Use the graduated cylinder again to measure 50 mL of the tiny beads. Determine the mass of the tiny beads, add to the marbles and swirl to mix. Pour this mixture back into the graduated cylinder; determine both volume and mass of the mixture. For each of the questions below, discuss with your partners, and write answers in your notebooks. Is the mass of the mixture equal to the sum of the marbles plus the beads? Is the volume equal to the sum of the two? 1 b) Repeat this activity with sand and the beads. Is the sum of the masses of 50 mL of sand and beads equal to the mass of the mixture? Is the sum of the volumes of sand and beads equal to the volume of the mixture? c) Repeat this again using sand and water. Be sure to use a very dry graduated cylinder for measuring the sand Is the sum of the masses of 50 mL of sand and water equal to the mass of the mixture? Is the sum of the volumes of sand and water equal to the volume of the mixture? In each of these activities, is mass conserved through mixing? Is volume conserved through mixing? Looking at the systems – sand and small spheres, and sand and water, why do the volumes behave as they do upon mixing? Check: describe your observations to the instructor, and provide an explanation for your observations. Suppose we had done this activity with materials with very similar particle size, for example salt and sugar. What would you expect the outcome to be, and why? Write a rule describing situations in which volumes of mixtures are conserved following mixing and in which volumes of mixtures are not conserved. d) Now repeat this activity using distilled water and ethanol – measure out as accurately as you can 50 mL of each, and determine the mass of each. Mix them in a 400 mL beaker, and swirl to be sure they are well-mixed. Then pour them back into the graduated cylinder and determine the final mixed volume and mass. Is mass conserved? Is volume conserved? 2 Applying your observation of mixing the large objects, what conclusions can you reach about the characteristics of water and ethanol? Check: share your rule with the instructor, and describe your observations about mixing water and ethanol. What does this say about the properties of these materials? 3 The Kitchen Kaper Chef Emeril was found murdered in his kitchen! He evidently had been preparing grilled pickles. The usual suspects were: Wolfgang Puck, Julia Child, Paula Deen, Paul Prudhomme, Jeff Smith, and Gordon Ramsey. Each of them had been covered with a mysterious white powder. Surrounding Chef Emeril were six bags of white powders that the chef had been using in preparation of the great feast. The powders were labeled with his secret code, so none would know the details of his special recipes. The bags’ labels were as follows: Foam Lea College (this one had been ripped) Blooms Buff Dear Since it was not at all clear what his code meant, it had to be assumed that not all of the powders were edible, for example they could contain rat poison to keep the vermin at bay, or plaster to seal up cracks in the walls, so none could be tasted to determine what they were. Furthermore, there was considerable evidence of a struggle. Chef Emeril was attacked by a vicious criminal, and he fought back valiantly. One of the bags had been ripped open, and its contents evidently had been spilled all over, and it was quite clear that the perpetrator would have some on his clothes. The problem is that chefs are always using interesting powders in their cooking so it is natural that chefs would be covered in whatever they had been preparing. The task of CSI BlueLicks is to identify the correct criminal using chemical and physical tests on each of the powders associated with the usual suspects. By comparing their properties with those of the bags, especially the bag that had been ripped open, The Culprit would be identified, and could be arrested. You have seven bags: a bag of “college” and one bag from each of the suspects. To keep the investigation scientifically controlled and free from bias, these bags have been numbered, and the actual source will be revealed at the end. 4 Note: in the following activities, you will be asked to record your observations. If you see nothing take place, the observation is not “nothing happened”, but rather you need more clarity and detail, such as – “when the brown drops were added, the color of the sample became a very light tan. “ The implication of this would be that nothing took place, but this is a conclusion and not an observation. Perform the following tests on each of the powders: 1. Observation test. Place a very small amount of each powder onto a dark surface, such as a piece of black construction paper, and examine with a magnifying glass. Describe your observations of each powder in your notebooks. Note each aspect of the powders – relative size, shape of crystals, if appropriate, color, whether they are homogeneous in appearance, and any other features that might be relevant. 2. Flame test. Place a very small pinch of a powder into the center of a 1”x1” square of aluminum foil and hold over a candle flame using forceps. Observe carefully the behavior of the powder over a couple of minutes. Record your observations in your notebook, including the behavior of the “college” reference sample. 2. Dissolving/phenol red tests. All of your powders should be observed side-byside with this test, including the reference sample. Place a slightly larger pinch of the powder into a well of the plastic spot plate, and add 1 mL of distilled water. Stir with the toothpick and observe whether the powder dissolves or not, and record this. This might be more easily observed against a black backgound. Next, add 2 drops of phenol red solution to each mixture, and observe and record what takes place. Rinse out the wells with distilled water before proceeding. 3. Acid test. Again, place a pinch of powder into the wells (side-by-side as before) and now add 1 mL of vinegar to each, and observe and record what occurs. Clean out the wells before the next step. 4. Iodine test. To a pinch of each powder, add ½ mL of water, stir, then 2 drops of tincture of iodine. Again, observe and record anything that takes place. Clean up the wells as before. Look at all of your data, and decide which powder was identical to the reference powder found at the crime scene. Since your results will be subject to severe crossexamination by the very well-paid defense team, you need to provide a complete list of the available evidence arguing in favor of your conclusions. Remember that even negative evidence is important, as it allows exclusion of certain suspects. 5