Diffusion Pre-assessment

Before learning about diffusion, you will complete a short pre-assessment below. This will help us understand what you as students learn through this unit. Research also shows that it actually helps learning to do some sort of assessment before starting learning. Watch the short video (Video 7.1.1) and then try to answer the questions in Exercise 7.1.1 as best you can. Please answer them without looking up any information. The point is for us (and also for you) to be able to see what you knew before the unit so we can compare it to what you learned afterwards.

Exercise 7.1.1: Diffusion pre-assessment questions
Not Currently Assigned

  1. Explain what change is occurring in the Video 7.1.1, and why you think the change is occurring.

    1. Sketch the path that an individual dye molecule might take after it has dissolved in the water until some time after equilibrium has been reached.
    2. Explain why the molecule would move the way you sketched both before and after equilibrium has been reached.

  3. The figure below shows a "concentration profile" which plots the concentration of the diffusing substance on the $y$-axis vs. position on the $x$-axis for a simplified skittle diffusion situation. Three different points in time are illustrated below the plot and the concentration profile is drawn for the first one, $t_0$, shortly after the skittle was placed in the water.

    Assume that there is a maximum concentration of dye that the water can hold and that at $t_0$ this concentration was already reached in the immediate vicinity of the skittle. Also assume that the amount of dye on the skittle is enough to saturate all the water. Sketch two more concentration profiles for:

    • $t_1$: a time around half way between $t_0$ and $t_2$
    • $t_2$: after the system has reached equilibrium

    Then give a brief explanation of why you sketched the concentration profiles as you did.