Video Demo: Conservation of Mass

How the heck do you teach the conservation of mass to 8th grade students?  Lab activities are always good, but what lab activity can be done without the students getting super confused?  Two components are required. First, a chemical reaction is needed.  It must use simple chemicals, and it should be obvious that a chemical reaction took place.  Second, it must be easily quantifiable. In other words the mass is easy to measure and it must show very clearly that mass was not lost during the chemical reaction.  I think I may have finally developed a lab activity that addresses both components.  Watch the video and download the student worksheet for more details.

Video Demo: Diffusion Across a Selectively Permeable Membrane

This is an updated version of a past demo.  Cell membranes are selectively permeable.  That is the membrane allows some materials to pass through and not others.  This allows the cell to maintain homeostasis, a condition in which the cell maintains the proper levels of needed materials.  In this demo the plastic of the bag acts as a selectively permeable membrane.  Iodine is small enough to pass through the plastic, while the larger water molecules are too big.  Watch the video on how to do it and to see what happens.

Video Demo: Food Coloring Diffusion

I bought a new video camera, so I decided to test it out.  Diffusion is a post that I did in the past, but I think the new camera makes it better.

Lesson: Let's Grub on Some Grass Beetles

Let’s Grub on Some Grass Beetles is a natural selection simulation. Natural selection is the “process by which favorable heritable traits become more common in successive generations of a population of reproducing organisms, and unfavorable heritable traits become less common.” In this activity, part 1 involves variations in silver beak loon beak types. There are tweezers, spoon, and knife shaped beaks. The beak best adapted to capturing grass beetles will survive and more chances to reproduce. The tweezers and spoon beaks are best adapted. The population of silver beak loons will change to a majority of tweezers and spoon beaks. Part 2 deals with variations in grass beetle color. The green grass beetles are best adapted to hiding in the grass than the orange or yellow grass beetles. In successive generations the populations of grass beetles will shift to green colors, since they will have the best chance to survive, reproduce and pass the variation to their offspring.

Watch the video and listen to the commentary on how to do the activity. Download handout: Let’s Grub on Some Grass Beetles

Video Demo: Rainbow pH

This demo comes from Flinn Scientific. Flinn provides a Chem Fax! service, which are free demos that Flinn emails you. This demo demonstrates the changing color of an indicator when pH changes. Here is the procedure:

1. 100 ml of a 0.1 M NaOH solution is added to 350 ml of distilled water in a 500 ml graduated cylinder.
2. 10 ml of universal indicator solution is added, which turns the solution dark purple, indicating a highly basic solution.
3. An Alka-Seltzer tablet is added, which results in carbon dioxide bubble being produced. The carbon dioxide gas causes carbonic acid production, thus lowering the pH (more acidic). The solution starts turning green, then to yellow.
4. When the Alka-Seltzer tablet rises to the top (due to the attached carbon dioxide gas bubbles lowering the tablet’s density), add 10 ml of vinegar to the solution. This will cause a bright red color to be produced at the top, indicating high acidity (low pH).