Law of Conservation of Mass

What I love about this lab: 

• brush up on TBB skills
• following directions skills
• making observations
• observing a chemical reaction
• formation of a gas
• mass of a gas
• an endothermic reaction, bottom of flask gets pretty cold!
• reading a chemical equation – shows that same elements are present before and after the reaction, no new elements are introduced or formed.
• formation of new molecules, the atoms are rearranged to form new substances that were not in the flask before.

The one thing that is not very clear to the kids is that the mass of the system before the reaction and after the reaction should be the same. Their results consistently show a loss of about 1 gram (on average) without releasing the gas from the balloon. When the gas was released, there was an additional loss of about 1 gram.  

For this experiment, there are 2 factors that can make the final mass different. The first factor may be leakage: gas, liquid, or both escaped during the active part of the chemical reaction. The seal formed where the balloon meets the flask may not be 100% airtight, even with the kids holding it. But if leakage does not happen, the second factor is buoyancy. When the balloon fills up with CO2, the volume of the balloon increases, therefore displacing the air around it. NSTA published a study about this and had results to show that there was a relationship between the volume of the balloon and the decrease in mass for the closed system.

Here is an excerpt from the published article: “Because the apparent loss of mass is not due to leakage, this relationship clearly demonstrates a buoyant effect. Archimedes’ principle states that any object submersed in a fluid will displace a volume of fluid equal to the volume of the object and the mass of the object will be reduced or “buoyed up” by an amount equal to the mass of the fluid displaced. Hence, when measuring the mass of an object in air (a fluid) on a balance, the mass that is measured is the conventional or apparent mass of the object. The true mass of the object would be the mass that would result if the object were massed in a vacuum.” (Science Scope, 2008)

A better example to show conservation of mass may be to place an ice cube or two in a small plastic snack bag, and to take timed measurements as the ice cube melts. (In a humid classroom, condensation forming on the outside of the bag could alter results.) Also, if using baking soda and vinegar, using a soda bottle without the balloon and capping it would keep the volume the same.

Overall, the kids enjoyed this experiment and it covered a lot of concepts that we studied. If you have done either of these experiments, please share your results!

Notebook:

pg. 110 – Law of Conservation of Mass

pg. 111 – Conservation of Mass Analysis

Changing Phases – Using a Venn Diagram

Smart Board Activity – Using a Venn Diagram to classify the states of matter and the changing phases.  The purpose of this activity was to visually represent how the states of matter and the phase changes are related to each other.

I pulled up the Venn diagram onto the Smart Board screen with the list of words and phrases listed on the right side.  This Venn diagram has circles/categories for solid, liquid, and gas. I reminded the students that wherever the circles overlap, it is something that both categories had to have in common, or it was a true statement for both. Where all 3 circles overlap, it is something that all 3 categories must have in common.

I divided the class into small groups.  I explained that each group would have a turn at the Smart Board, sending one person at a time as their representative. In their small groups, the students discussed amongst themselves what words or phrases they would like to place into the Venn diagram. They also had to decide who would go first, and so forth. I set this activity up to be a friendly competition to see which group can get the most items placed into the Venn diagram correctly.

Using the tri-fold brochure for their note taking, they took notes in blue or red colored pencil. They used the blue colored pencil for the phrases that were in blue and related to the properties for each state of matter,  red for the words that were in red and referred to each of the phase changes.  They only wrote down the answers if they were placed correctly into the Venn diagram, I didn’t want them working ahead.  This kept their focus on the board. If a student did place a word/phrase into the wrong spot, I moved it back to the list on the right.  The next team could either correctly place the word/phrase into the diagram or choose a new word/phrase.

From start to finish, this activity took about 25 minutes. Overall, the activity went really well and the students were engaged and enjoyed the friendly competition.

For HW, students will review the terminology related to phase changes, as well as read about hot water freezing faster than cold water.

Handouts:

pg. 53 – Phase Change Vocab

pg. 54 – BrainPOP: Phase Changes Activity

pg. 55 – Review: States & Phases Venn Diagram

pg. 56 – Read About it: BrainPOP – hot water freezes faster?

States of Matter

Today we talked about the phases of matter and I broke the lesson up into 4 different activities using a variety of strategies.

Part 1 – Brief introduction to set the stage

I told the students to place their hands on the table and close their eyes.  I then asked them “Is the table moving?” Variety of answers.  I told them that the table is made up of billions of atoms that are vibrating, we just can’t feel it.  Atoms do not stay still, I mentioned absolute zero and how scientists think that atoms would stop moving at this extremely cold temperature. Last I checked, we got really close but have not reached absolute zero yet.  

Keeping their eyes closed, I ask them if they feel the air molecules hitting them right now.  Gasses move very quickly and are bouncing around the room, hitting each other, bumping into the wall, off the ceiling, off the floor, kind of like a pinball machine.  I also ask them to take a deep breath – the air is filling up their lungs.  I also mention that they are breathing the same air that the ancient Greeks and Australopithecus did (they just studied early man in History class).  All the matter on Earth has always been here and is constantly recycled.  The oxygen you are breathing right now was once part of a water molecule, or part of an animal, etc… They think its cool and gross at the same time, of course!

Part 2: BrainPOP movie on States of Matter.

I show the movie and paused it when it zoomed into the glass of water and showed the water molecules.  I ask the kids, “What do you notice about how the atoms are arranged?” We discuss it and I have them draw the atoms, in a color of their choice,  into their notes in the liquids box. Continue the movie.

Paused the movie again when it zoomed into the gas atoms up close.  ”What do you notice about how these are arranged compared to the liquid?”  Using a different color, they draw the gas atoms into the gas box.  Continue the movie.

Paused again when it zoomed into the solid atoms up close. “What do you notice about how these are arranged compared to the liquid and gas?” They came up with great observations, such as many more atoms, close together, not a lot of empty space between each, and they were neater – arranged almost in a pattern. Using a third color, we drew in the atoms for the solid.  Played the rest of the movie.

Part 3 – Notes – Jigsaw/read aloud

I assigned a paragraph to each group and gave them about 3 minutes to complete their assigned section.  Once they were done, each person in group 1 read a sentence out loud to the rest of the class. Student 1 read the 1st sentence, student 2, the next, and the group continued until the whole paragraph was done.  I used 3-4 students per group for this activity.

The other groups/students listened and filled in their notes.  We then moved to group 2 for the second paragraph, and so forth.  This worked really well.  Some of the kids noticed that it was exactly the same as the movie, which it was, I made a transcript and cut out important words and placed them in the word bank.

Part 4 – Closure using the matrix

Using the BrainPOP graphic organizer, we reviewed the main concepts that we learned today, making sure to fill it in completely and correctly.

Homework: cut ‘n paste vocabulary to review terms we discussed today.

Resources:

BrainPOP Movie: States of Matter

pg. 50 – BrainPOP: States of Matter Notes

pg. 51 – BrainPOP – States of Matter Graphic Organizer

pg. 52 – States of Matter Vocab