No Series: Conservation of Mass

Conservation of Mass

Lesson Objective: Student chemists prove conservation of mass with 3 quick labs
Grades 9-12 / Science / Chemistry
5 MIN

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Discussion and Supporting Materials

Thought starters

  1. How do the 3 short labs help solidify conservation of mass for students?
  2. Notice how Mr. Forrest concludes each lab by summarizing results and posing clarifying questions How does the popcorn lab help students distinguish between mass and volume?

12 Comments

  • Private message to Melanie Edens

How do you safely dispose of the lead nitrate mixed with the potassium iodide? Is this really safe for the kids to handle? I am reading I would have to arrange special hazardous waste disposal.

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  • Private message to Eric Weis

The teacher needs to come up with a way to weigh the gas evolved in the second demo--otherwise the students can't tell if the rule is true or not. We want science students to infer rules from experiments, not to rationalize backwards from a rule given by the teacher. The way he presents his demos, the rule "mass stays the same during a chemical reaction" comes from the first demo. Then, in the second, he says since mass stays the same during a chemical reaction, the missing mass must have gone somewhere else. That's not clear thinking.

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  • Private message to Ian Kastelic
Dude! Where are your goggles!!??!!
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  • Private message to Grace Salibay
where can i find the lesson plan for this video?
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  • Private message to Stephen Princiotta
I have used microwave PC and measured mass before and after. You can also note the change of state as you get a loss of 8g of mass overall from the water vapor escaping from the kernels during the popping process.
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External Resource Materials

Transcripts

  • Summary

    Three lesson planning ideas for short, snappy chemistry experiments for Key Stage 3 lessons, designed to help pupils explore the

    Summary

    Three lesson planning ideas for short, snappy chemistry experiments for Key Stage 3 lessons, designed to help pupils explore the principle of conservation of mass.
    Chemistry teacher Jack Forrest carries out a number of quick and simple experiments with his Year 7 class, to reinforce the idea that mass is always conserved. These experiments would also work well with lower age groups.
    First, the students mix colourless solutions of potassium iodide and lead nitrate together, to form a bright yellow mixture, demonstrating that a chemical reaction has taken place. They weigh the solutions before and after mixing, noting that the mass remains the same.
    Next, Jack demonstrates a classic Carbonate reaction, reacting marble chips and hydrochloric acid. The class discuss why the mass decreases in this reaction. Lastly, he cooks popcorn kernels which increase in volume when boiled, but the mass stays the same.