Observing the Principle of Conservation of Mass

The purpose of this experiment is to determine whether water conserves mass when it undergoes a phase shift through the various states of matter.

Research Questions:

• Why does the mass of a substance remain the same through a phase shift?
• How can we measure the mass of a substance?
• What ways can a substance undergo an internal change?
• What is a chemical reaction?

The law of conservation of mass states that the mass of a given quantity of a substance will remain constant despite internal changes to that substance. This means that matter that undergoes a phase shift, such as turning from a liquid to a solid, will remain at a constant mass. This principal also applies to chemical reactions in that the sum of the masses of two combined chemicals will equal the mass of the resulting product or products. Matter is neither destroyed nor created during phase shifts or chemical reactions.

Materials:

• Water
• A stove or a Bunsen burner
• A freezer
• A graduated cylinder
• A scale
• A freezable container
• A glass distilling flask

Ask your science teacher if you can borrow some of the science supplies you need for this experiment or if you can have access to the science lab. Alternatively, you could order supplies from a science catalogue.

Experimental Procedure:

1. Measure the mass of an empty graduated cylinder.
2. Using the graduated cylinder, measure out 100mL of water.
3. Measure the mass of the water in the graduated cylinder.
4. Record all measurements on a chart such as the one below.
5. Subtract the mass of the graduated cylinder from the mass of the water and cylinder combined. This is the starting mass of the water.
6. Measure the mass of the freezable container
7. Pour the water into a freezable container, making sure that all the water has been transferred.
8. Measure the mass of the freezable container with the water in it.
9. Subtract the mass of the freezable container from the mass of the freezable container with the water in it. This number should be the same as your answer in step 4.
10. Freeze the water.
11. Once the water is frozen solid (a few hours) take the mass of the frozen water while it is still in the freezable container.
12. Subtract the mass of the freezable container from the mass of the freezable container with the water in it and record the result.
13. Allow the ice to melt.
14. Return the water to the graduated cylinder and measure the volume.
15. Measure the mass of the water in the graduated cylinder.
16. Subtract the mass of the graduated cylinder from the mass of the water and cylinder combined.
17. Take the mass of the glass distilling flask.
18. Pour the water into the glass distilling flask, making sure that all the water has been transferred.
19. Measure the mass of the water in the glass distilling flask.
20. Subtract the mass of the glass distilling flask from the mass of the water and glass distilling flask combined.
21. Set up the Bunsen burner and with the glass distilling flask on it and the distilling pipe (the pipe leaning off to one side) leading back into the graduated cylinder.
22. If the pipe leading straight up from the water reservoir is open, place a cork or rubber stopper in it. Heat the water in the glass distilling flask until it completely boils away.
23. The water should now be in the graduated cylinder once again.
24. Measure the mass of the water in the graduated cylinder.
25. Subtract the mass of the graduated cylinder from the mass of the water and cylinder combined.

Terms/Concepts: Conservation of mass; Phases of matter; Phase shift; Liquid; Solid; Gas; Chemical change; Closed system; Mass

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