Embedded Files
Title: Missing Mass - Conservation of Mass
Principle(s) Investigated: Conservation of Mass, Density
Standards:
HS-PS1-7. Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.
- [CCC-5] matter is conserved
- [SEP-3] investigations
Materials:
Students:
Notebook, Pencil/Pen
Teacher:
4 x 500ml Volumetric Flasks w/ stoppers
2 x 1000ml Volumetric Flasks w/stoppers
2 x food coloring
Water
+500ml Ethyl Alcohol
2 x pipettes
2 x 200ml beakers
Procedure:
1. First, weigh all of the volumetric flasks (including stoppers)
2. Record the mass.
3. Fill THREE of the 500ml volumetric flasks with water to the indicated mark using the pipettes as needed for accuracy, add a few drops of BLUE food dye, put in stopper, and gently mix.
4. Fill the last 500ml volumetric flask with ethyl alcohol to the indicated mark using the pipettes as needed for accuracy, add a few drops of YELLOW food dye, put in stopper, and gently mix.
5. Reweigh the flasks, and calculate the mass of the contents of each.
6. Record the mass of the contents.
7. Using a funnel add combine 2 flasks of water into the larger 1000ml flask, and gently mix. Weigh the full flask and then calculate the mass of the contents.
8. Record the mass of the combined contents. (Should equal the sum of the individual 500ml flasks of water)
9. Observe the new volume.
10. Repeat steps 7-9 with one flask of water and the flask of ethyl alcohol. (the mass should be summative, but the volume should be visibly reduced. )
Student prior knowledge: This is to act as an introduction to measuring and the conservation of mass. Students should know the general lab safety protocols.
Explanation:
The law of conservation of mass states the total mass of any material system is neither increased nor diminished by reactions between the parts. Students may incorrectly assume that volume is also a conserved quantity however this demo will allow the students the opportunity to see that two liquids can be mixed and the volume is reduced even though the mass was additive.
Some factors that cuase the observed phenominom:
Miscibility
A PHYSICAL PROPERTY. This refers to the ability of liquid solutes to mix. “Mixiblity”
Intermolecular forces
Dipole–dipole interactions are a type of intermolecular attraction—attractions between two molecules. Dipole-dipole interactions are electrostatic interactions between the permanent dipoles of different molecules. These interactions align the molecules to increase the attraction.
Questions & Answers:
1. In a closed system, a chemical reaction takes place. The mass of the reactants in the beginning of the reaction is 25g. What does the mass have to be in the end of the reaction in order to follow the law of conservation of mass?
- Mass is conserved, so so the mass of the reactants should equal 25g as the reaction took place in a closed system.
2. In a chemical reaction, the mass of the reactants was 15g. The mass of the products was 12g. Did this chemical reaction follow the law of conservation of mass?
- The law of conservation of mass/matter states matter cannot be created or destroyed, and all chemical reactions follow this law, so yes. However, because this was not in a closed system the 'missing' 3g of products were most likely lost to the surroundings, or due to some error.
3. There are two reactants in a chemical equation, and one product. The mass of the product is 30g. The mass of the first reactant is 17g. What must the mass of the second reactant be, if the equation is to follow the law of conservation of mass?
- Assuming a closed system, the mass of the second reactant would be 13g.
Applications to Everyday Life:
Conservation of Mass
Calculating density
Density of solutions (different ratios of solutes)
Solubility of liquids
Intermolecular Interactions
Organic Chemistry - Alcohols
Photographs:
This picture shows the visual difference of the volume when the water and ethyl alcohol are mixed into the larger flask.
Videos:
<iframe src='https://www.carolina.com/teacher-resources/Interactive/chemistry-lost-volume-demonstration/tr10785.tr' allowfullscreen frameborder=0></iframe>
Adapted from Carolina (The Lost Volume)
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