Week 1 – Models of Mass

Exploding Can Demo:

Students observed a can containing natural gas as it was lit, as the gas burned, and finally the can “exploded.”  They then drew diagrams on a whiteboard of their models for understanding of what took place, trying to explain what happened as best they could.


Many incredible things happened:

  • Your groups actively discussed and debated your understandings.
  • You worked together to decide what to put on your whiteboards.
  • You explained and defended your reasoning with your groups and to the class.
  • You asked clarifying and probing questions about your own and others’ models.

Hopefully, it’s clear how working in groups, sharing whiteboards, and having a discussion is a great tool to help build understanding.

Conclusions: In chemistry, we have to describe things and create models for things that we cannot observe directly. In our class, we are less concerned with the “right” or “wrong” model—only whether models are more or less helpful to aid our understanding of what is going on. As such, the key questions that we need to ask of each other are:

  • Is the model consistent with the observations that were made?
  • Does the model help me understand what is going on?
  • Is the model general enough that it can be useful as it is applied to new or different situations–does it help explain what is happening?

Mass Change Lab

Watch this video to help clear up what mass means:

Ring of Truth – Changes in Sparklers

Ring of Truth – Conservation of Mass 1

Ring of Truth – Conservation of Mass 2

Then, we measured the change in mass for several changes.

  1. Expanding Steel Wool
  2. Burning Steel Wool
  3. Mixing Two Chemicals
  4. Dissolving Alka-Seltzer

We whiteboarded diagrams showing the changes that occurred.  Here are some sample whiteboard particle diagrams and corresponding explanations.

Steel Wool Expanding:

The mass decreased a bit because some particles fell off onto the table when it was expanded, so some particles were lost (fewer particles –> less mass).

Steel Wool Burning:

Air (oxygen) particles were added to the steel wool when it was burned, so the mass increased.

Dissolving Alka-Seltzer:

Particles from the alka-seltzer tablet became fizz (bubbles), which escaped the cup and went out into the room, so the mass decreased.

Mixing 2 Chemicals:

The mass stayed (almost) the same during this change.  If it went down very slightly, it may have been because some of the chemical evaporated or a little bit spilled/splashed when they were mixed.

Labs & Homework assignment due Monday:

LabPacket – Week 1

Homework – Week 1 – Mass

Hint on Homework:
(2d) When iron rusts, the iron combines with oxygen from water or the air to form iron oxide (rust)

Post any questions you may have in the comments.

Quick quiz on Tuesday on mass conservation concepts.

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