Tag Archives: conservation of mass

Conservation of Matter

After reviewing the homework problems assigned for Lesson 7, students were reintroduced to the Copper Cycle.  Because the Copper Cycle experiment involves steps that must be conducted in a fume hood, we opted to watch a video (below), with students taking observations on their Copper Cycle handout.  For reference, students also received a copy of the Copper Cycle experimental procedure.

After the video, we discussed the concept of Conservation of Matter, transitioning to Lesson 8 in the textbook.  Because Lesson 8 continues an investigation of the Copper Cycle, and we are unable to safely conduct that lab, we instead investigated the related concept of Conservation of Mass.  Students participated in a classroom demonstration which involved combining baking soda and vinegar in a closed system and experimentally demonstrating that mass is conserved.  We measured the starting and ending mass, noting the slight decrease in mass at the end due to experimental error (vinegar and carbon dioxide leaking slightly).  At the end of the experiment, we removed the inflated balloon and noted a decrease in mass of 0.2-0.3 grams, indicating the carbon dioxide gas has a measurable mass.  Students also noted the change in volume of the products as evidenced by the partially inflated balloon compared with the volume of the reactants.

For homework, students were provided with a copy of the Penny Lab to read over in advance of Wednesday’s class.  Students were also reminded that a signed syllabus and safety contract must be turned in to enable participation in the lab.

Materials, Mass, and Volume
Chemical Reaction


Chapter 17: Toxic Cleanup

For Chapter 17, students will each participate in a project designed to meet the learning targets of the chapter while de-emphasizing the focus on daily worksheets.  Students are still responsible for reading the individual lessons in the chapter and applying their learning to the project.  While the project is an individual assignment, students are encouraged to collaborate and time will be allocated for students assigned the same topic to share and compare their work.

Part 1: Locate your assigned reactant pair below.  Each reactant in the pair is hyperlinked, and the link will take you to the Material Safety Data Sheet (MSDS) for the chemical.  The MSDS contains 16 different sections.  Read through the sections, locate the following information for both reactants, and summarize in a Google Doc:

  • Chemical Name
  • Chemical Formula
  • CAS #
  • Oral LD50 for Rat

Next, read through MSDS Sections 4-16.  Summarize the most important information relating to safety, exposure, handling, and disposal.  If the information for proper disposal is not specific, refer to the schools chemical database on the King County Rehab the Lab website.

After locating and summarizing the information above, use the rat LD50 (oral exposure) to calculate the LD50 for a human with a mass of 80 kg (176 pounds).  Repeat for humans with a mass of 50 kg and 20 kg.  Graph the results in Google Sheets and then copy the graph into your Google Doc.  For step-by-step instructions, watch the video below:


Reactant Pairs:

  1. NaCl + KNO3
  2. NaClMg(NO3)2
  3. NaClCu(NO3)2
  4. NaClAgNO3
  5. Na2CO3 + KNO3
  6. Na2CO3Mg(NO3)2
  7. Na2CO3Cu(NO3)2
  8. Na2CO3AgNO3
  9. NaOH + KNO3
  10. NaOHMg(NO3)2
  11. NaOHCu(NO3)2
  12. NaOHAgNO3

For specific information on NaOH toxicity, view page B2 of the BASF Chemical Emergency Medical Guidelines document.

Part 2: Next, determine the missing product of your assigned reaction.  To assist in your efforts, one of the two products is provided:

  1. NaCl and KNO3 → NaNO3 + ?
  2. NaCl and Mg(NO3)2 → NaNO3 + ?
  3. NaCl and Cu(NO3)2 → NaNO3 + ?
  4. NaCl and AgNO3 → NaNO3 + ?
  5. Na2CO3 and KNO3 → NaNO3 + ?
  6. Na2CO3 and Mg(NO3)2 → NaNO3 + ?
  7. Na2CO3 and Cu(NO3)2 → NaNO3 + ?
  8. Na2CO3 and AgNO3 → NaNO3 + ?
  9. NaOH and KNO3 → NaNO3 + ?
  10. NaOH and Mg(NO3)2 → NaNO3 + ?
  11. NaOH and Cu(NO3)2 → NaNO3 + ?
  12. NaOH and AgNO3 → NaNO3 + ?

As with the reactants, repeat the review process with the NaNO3 MSDS.  In addition, after correctly solving the equation for the missing product (confirm your answer with Mr. Swart), search for the MSDS for the confirmed second product and again work through both the MSDS summary process and the LD50 calculations with graphing.  A simple Google search for the chemical formula and MSDS will help you locate the MSDS.

Now that you know all of the reactants and products in your assigned equation, balance the chemical equation.  Practice balancing the remaining equations by first solving for the unknown product and then balancing them out.  Record all of your work in your Google Doc.  We worked through multiple examples on the white board and the work is pictured below:

Part 3: Focusing once again on your assigned chemical reaction, calculate the number of grams per mole of each reactant and product.  Does the total reactant mass equal the total product mass?  Why or why not?  Show how you can use the mole ratios (the numbers written in front of your balanced equation) to demonstrate the Law of Conservation of Mass.  Again, record your work in your Google Doc.  Compare your work with the other students who were assigned the same reactants as you were.  You will be working together as a small group to complete the lab portion of this project.

Part 4: Lesson 90 lab!  Students combined the reactants from their assigned chemical reaction and created a class data set by reporting whether or not the products formed in their reaction produced a solid.  The Lesson 90 Worksheet provides details of the lab.  Our class results are shown below.  Note: according to the textbook, reactions 6 and 10 also should have produced a solid product.

FullSizeRender (2)

Part 5: For the final part of the research report, students should update their data to include which chemical reactions from the Lesson 90 lab produced solids and which did not.  The research report should include a discussion of questions 5 and 6 from the Lesson 90 Worksheet.  Explain why you think mixing certain compounds produces a solid while other mixed compounds remain in solution.  Research reports are due Wednesday, June 1.

Research Report Checklist

□ For both of your assigned reactants and the products formed after the reaction:

  • Chemical Name
  • Chemical Formula
  • CAS #
  • Oral LD50 for Rat

□ Summary of MSDS sections 4 through 16.  Note: summarize each section in one sentence, focusing on the theme of the section rather than specific information.

□ Calculate the lethal dose for a human with a mass of 20 kg, 50 kg, and 80 kg using the oral rat LD50 for all 4 of your compounds.  Graph the results with mass on the X axis and lethal dose on the Y axis.  Copy the graph into your Research Report.

□ Balance all 12 of the reactions, solving for the missing product in each reaction.  Remember to first balance the individual compounds based on charge, and then balance the overall equation using molar ratios.

□ For your assigned reaction, calculate the molar mass of each compound in your reaction.  If the reaction is properly balanced, the reactant mass will equal the product mass.

□ Include the results of the Lesson 90 lab, specifically including which products formed solids and which did not.

□ Discuss what generalizations you can make about the results of mixing aqueous salt solutions.

□ Apply your learning by predicting what solutions you could mix together to form Ca(OH)2.  Repeat for ZnCO3.  There are many possible solutions.  Identify one solution for each product.

□ Share your Research Report with Mr. Swart.

□ Explore the Recology CleanScapes website and the King County Household Hazardous Waste Collection Options website for information about how to properly dispose of (and identify what is and is not hazardous) different household waste products.

□ Should you be concerned about lead and arsenic contamination from the Tacoma Smelter Plume?  Visit the Washington State Department of Ecology website to learn more about this important public health issue.

□ Locate your address on the map to find out how your environment has been impacted.

□  Given that much of the soil in south King County has been contaminated by the smelter, visit the learn more about cleanup options by reading through the Dirt Alert Soil Sampling Brochures available on the Dept of Ecology website.

□ How will you use information like this when considering where to live in the future?

Matter, Atomic Structure, and Bonding: Conservation of Matter

We worked through the remainder of the Lesson 8 worksheet today, tracing copper as it moved through the copper cycle and learning about the Law of Conservation of Mass in the Lesson 8 PowerPoint.  We concluded the class with a demonstration.  Most students were familiar with the chemical reaction of adding vinegar and baking soda together (it bubbles!).  Students looked up the chemical formulas for both reagents and we discussed the products that are generated from combining the reactants (baking soda and vinegar).  Students learned that the products of the reaction are sodium acetate, water, and carbon dioxide gas.  The following question was posed: If a known amount of baking soda and vinegar were combined together in an open container on a scale, what would happen to the final mass of the products remaining in the container on the balance.

For the experiment, 5 grams of baking soda were added to 59.6 grams of household vinegar (5% acetic acid in water) in a flask placed on a digital balance.  After a few minutes, the reactants stopped bubbling, and the mass of the remaining contents in the flask were found to be 57.5 grams.  Therefore, the difference of 2.1 grams (59.6 grams minus 57.5 grams) should be the mass of the carbon dioxide gas released into the atmosphere.  Tomorrow, students will conduct their own experiments and be tasked with using our available technology to evaluate the Law of Conservation of Mass for a given set of reactants.