Today we are learning to: Represent “what we can imagine” about the micro-world based on “what we can see” in the macro-world Articulate these imaginings as clearly as possible Identify “stuff” as matter Recognize that all matter has mass and takes up space Identify one way to describe matter quantitatively

Homework (9/10/13) Students will observe a demonstration involving a coffee can, partly filled with methane, and changes to the flame as the methane burns. Students will make careful written observations and using evidence, postulate what might be occurring at particle level inside the can. Create a time-series of drawings to represent changes at the particle level throughout the demonstration.

Particle diagrams can be used to illustrate: Uniformity of particles. All methane particles have the same symbol. Mixtures of different particles. Oxygen is symbolized differently from methane. Changes in density Differences in concentration within a volume. Changes in relative speed.

9/16/13 Math Concepts Take a wooden block and a ruler. Measure and record the length of your block in each of three dimensions. Calculate the volume of your block in cubic units. Show your work as you would if you were being graded for a test.

9/16/13 Math Concepts (check your work) Did you measure the length in metric units? Metric should always be your default measuring unit (unless a specific problem or measuring tool obligates the use of nonstandard units) Have you measured precisely to the nearest mark on your ruler, and included one more estimated digit in your reported measurement? With these rulers you should be able to read to the nearest 1/10 cm, estimate to 1/100 cm. Did you show units on both the left and right side of your equation? Do the units balance? As a final step in your calculation, have you considered the significant figures in your measurements, and rounded your final answer to the correct number of significant figures?

Part 1 – Mass of steel wool Apparatus Balance Small wad of steel wool (~ 1/4 of a pad of #1 steel wool)   Lab performance notes Students should determine the mass of the wad of steel wool. Students should carefully pull the wad apart so that it occupies a volume roughly twice as great as before. Students then determine the mass of the expanded wad of steel wool.

Part 2 – Mass of ice and water Apparatus Balance Small vial and chip of ice   Lab performance notes Students should find the mass of the vial + a small piece of ice. Ice takes a while to melt. You can speed the process by warming it with your hands, or by setting aside your (labeled) vial and working on another part of this series of activities. Find the mass of the vial and water after the ice has melted.

Part 3 – Mass of a precipitate Apparatus Balance Two small vials 0.1M solutions of Ca(NO3)2 (16.4 g per liter of solution) and Na2CO3 (10.6 g per liter of solution). 300 mL of each should be sufficient for a class of 12 groups. Lab performance notes Students should fill each of the vials no more than 1/3 full of the solutions. Cap the vials and find the mass of both vials together. Then pour the contents of one vial into the other; carefully, so not to spill. Once a reaction has been observed, mass both vials and their contents again. Dispose of waste in the approved container at the front desk.

Part 4 – Mass of burning steel wool Apparatus Balance Bunsen burner Small tuft of steel wool Evaporating dish Crucible tongs Safety precaution: This activity involves open flame. Lab performance notes Steel wool must be fluffed out until it has almost the appearance of a cobweb. Place the steel wool on an evaporating dish, and mass it. Ignite the steel wool by touching on several sides with a 9 volt battery. Note carefully any changes in appearance. Mass the final product once it has cooled down.

Part 5 – Mass of dissolved sugar Apparatus Balance Vial with cap Sugar Lab performance notes Students should fill a vial about 1/2 full of water, then put about a 1/4 tsp of sugar in the cap of the vial. Mass both of these reagents. Carefully pour the sugar into the vial, taking care not to spill any. Swirl gently to dissolve. Once the sugar is dissolved (as completely as possible, mass the solution again.

Part 6 – Mass of dissolved Alka-Seltzer  Apparatus Balance Vial with cap Small piece (1/4 tablet) of Alka-Seltzer Lab performance notes Students should fill a vial about 1/2 full of water, then put the 1/4 tablet of Alka-Seltzer in the cap of the vial. Mass both of these reagents. Add Alka-Seltzer into the vial, covering only LOOSELY with the cap. Record observations. Once there is no more evidence of a reaction, mass the solution, vial and cap.

Counting particles Since we can’t “count” individual matter particles, what can we measure to compare the amount of matter in a sample before and after an experiment? Does the amount of matter ever change as a result of an experiment?

“Hypothesis of Conservation of Matter” In a closed system, matter is never created nor destroyed by any process. In an open system, matter can be added or taken away from a place outside the defined system.

Does the data confirm the hypothesis? Taking the class data as a whole, for each of the six experiments, does the class data confirm the hypothesis, that there is no change in system mass? Looking at the data individually, which data points represent large deviations from the class consensus. Can you provide explanations for these deviations? Or what question might you ask the group that posted the data? Which data represent smaller deviations from the class consensus, which might be explained away simply as measurement uncertainty? For those systems where class consensus show mass not conserved, can you explain with evidence that it was not a closed system? Draw a particle diagram representing each system (before and after the change)