Activity 2: Diffusion of Color Through Water

Will substances in fluid behave similarly to substances in air? Can we use water to model diffusion?

  1. Divide the class into six groups to explore the effect of grid size and time steps on results.

     

      Group A Group B Group C Group D Group E Group F
    Grid Size 1" 2" 3" 2" 2" 2"
    Time Step 5 seconds 5 seconds 5 seconds 5 seconds 20 sec. 1 minute

  2. Have each group place one grid sheet into the protective sleeve and place at the bottom of their pan.

  3. Each group should have a set of grid sheets to record their results for each time step.

  4. Fill each pan with room-temperature water.

  5. Place 3 drops of food coloring into the center of the pan. This is time step 0.

  6. At the appropriate intervals, record which grid squares have been "colored" by the food coloring. You may want students to record each time step on separate grid paper, or one sheet with different colors representing different time steps.

  7. Continue until all squares have been covered, or a significant amount of time has elapsed with no change in coverage.

    DISCUSSION:
    RESOLUTION (Grid square size)

    TIME STEPS:

  1. Introduce the second Excel model on an overhead projection and have students compare the resulting graph to their results.

Download Excel Model of Color Diffusion

Notes for Using Excel Diffusion Model

Teaching Strategies, Questions, and Assessment

In the first activity students were challenged to document the movement of a scent [vanilla evaporating and moving] through the air in their classroom.  In the discussion to achieve a "fair" experiment, students were asked to hold constant the variables that might affect their results.  This activity allows students to observe, measure, record, and analyze the effects of the time and sampling variables.  However, since it might be difficult or impossible to see the outcomes with a scent [gas], we will use another fluid [water and food coloring] to test the behavior.

Sample Rubric Items 0 1 2 3 4
Student describes the movement of particles (1) as moving from the drop toward the water(2), includes factors such as randomness in motion, collisions with other molecules, speed of particles relative to temperature, possible interactions with container (3--->4).
Student discusses the variables of location and time and recommends a plausible method for doing this in the classroom(1-->2).  Student uses the manipulated (independent) and responding (dependent) variables, and includes some needed constants, such as temperature, motion, distance drop is delivered to the water, etc.(3).  Student specifies a method that includes careful measurement of time and location through the use of a grid or ruler.           
  1. You may alternatively offer your students more directed information through a series of questions, such as:  Describe how the colored particles move in the container.  What factors can influence how the colored particles move? 
  2. Use the embedded assessment results and reflect back on the students' experiment with the vanilla scent in the classroom.  Post the variables that the class decided needed to be controlled.  Now, pick 2...time and regular seating, and ask your students to split up into 4 groups.  Ask 2 groups to plan an experiment to test for the best time intervals and the best way of gauging location.
  3. Offer your students access to the materials list above, but include:
  4. Allow just 10 minutes for the individual groups to plan, and then ask them to share their ideas and come up with a best plan for each variable.  You should interact with each group and ask them to be sure they can communicate the method clearly.  They may want to write out a procedure or flowchart to clearly show the final method. Use an interview to push each student to be able to identify the independent and dependent variables, and the constants in their experiment. 
  5. Ask your students to independently write-out a sentence [hypothesis] to describe what they think will happen.  You may want to give them a template to follow:  If the [independent variable] is changed to_______________________ then the [dependent variable] will.....
  6. As the students run their experiments, and individual pairs run different versions of the independent variables of time intervals and grid sizes, again move from team to team coaching them on what they are seeing.  If they do not think something went right, suggest they do it again with a second or third trial.  Ask them to reflect back on the "Kid Diffusion" activity and ask them how they feel about the results from just 1 trial versus 5 or 10 trials.
  7. Teams should combine their varying trials for a class presentation on the effects of grid size and on the effects of different time intervals.  As a team they should decide on how they might best communicate their results, and what conclusions they can make.  Push the teams to make graphs that help to visualize the relationships.  For concluding discussions suggest they follow the questioning strategy suggested in Julia Cothron's book on "Students as Researchers".  The strategy follow a simple progression: 
    1. What was the purpose of your experiment?
    2. Was the hypothesis supported?
    3. What were your major findings [explain, not list raw data]?
    4. Do the results agree with other experiments or understandings about the world?
    5. What can you conclude?
    6. What other conditions may have influenced your results and what would you recommend for further study?
  8. Ask students to use the following rubric to rate the teams' presentations.  Use their responses as another embedded assessment.
Sample Rubric Items 0 1 2 3 4
Students use appropriately labeled tables and graphs in their presentation.
Comments to support score given:

 

 
Students supported their conclusion with data and clear explanations.
Comments to support score given:

 

 

 

          

 

Return to Diffusion Module

Return to Warm-up Activity

Return to Activity 1

Go To Activity 3