Water Filtration by Evan James



Have you ever wanted water to drink and not been able to get to it?

  • What are some problems people face if there’s a natural disaster like Katrina?
  • Who has safe water to drink? Why?
  • Who does not have safe water to drink? Why?
  • Video clip  of folks in Haiti collecting water (http://www.youtube.com/watch?v=UrHYlIAxYC8).
  • Why types of things contaminate water?
  • What are some historical and current obstacles for aid organizations helping developing countries?
  • How can you make water safe to drink?

Flow of lesson:

  1. Introduce problem with a worldwide/political/economic/social context.
  2. There are three systems to investigate:
    1. 1 micron latex (1 drop/1000 mL H2O) Simulates the same size as a bacterium.
    2. Sand and water
    3. Salt and water
  3. These three mixtures are examples of homogeneous mixtures, homogeneous mixtures and colloids which are key topics in physical science.
  4. Systems can be made by teachers or by students at instructor discretion.
  5. The expectation is that through a class discussion the idea of filtration will naturally come up.
  6. Students will then hypothesize about which systems can be successfully filtered through paper filtration.
  7. Instruction on proper technique should be provided.
  8. Testing the conductivity of the salt solutions before and after filtration is recommended. The students can bring their samples to the instructor and only one sensor is needed.  (Extension: have students create their own conductivity sensors)
  9. Students filter all three mixtures and make observations.
  10. Discussions follow on how to model on the molecular level what they observed in lab. Discussions of scale will be very important. Metric conversions can also be introduced at this time.
  11. Finally a discussion about how to engineer a better filtration system should be initiated.
  12. This problem is currently being investigated by a large team of researchers at UMaine.




Note: No hand-out is needed, but there is an expectation that the use of lab notebooks will be employed.

ASSESSMENT (free response):

  1. Under what circumstances is using a paper filtration system effective for decontaminating water? Explain.
  2. Under what circumstances is using a paper filtration system not effective? Explain.
  3. If the pore size of a filter is decreased to a large extent, what is one potential problem with engineering a filter with extremely small pores? Explain.
  4. If you were to coat the paper with a substance in order to alter the paper, what are five properties you would want the substance to have.
  5. Consider the video presented during this unit. What are some obstacles (societal, political, cultural and economic) associated with providing clean water technologies to people in developing countries?

ASSESSMENT BACK UP (fill in the blank):

1.              Order the following by size from smallest (1) to largest (3)

Particle Size (l-3)
Positive ion (cation)

2.              Complete the following table regarding solutions, suspensions, and colloids.  Recall that we examined the properties of each in our first experiment.  Is the appearance clear or cloudy after filtration?


Item Particle size (1-3) as in question 1. Appearance after filtration.


3.              Rank the following particles by relative size from smallest (1) to largest (4).


Particle Size (1-4)
Gaseous molecules






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