Chapter 3-Mixing and Moving in the Environment Turbidity

Overview: Water quality varies with several factors, including: contaminants and other things that might show up in the water, the standards or limits of water quality we will accept or tolerate, and the history and processes the water goes through before it is used. In essence, almost anything can be considered a "potential" contaminant. Correspondingly, do not view anything physical, chemical or biological as a contaminant until it is in the water supply. How water behaves affects how contaminants behave.

Purpose: The purpose of this lesson is to show that the physical environment in which the contaminant is placed strongly influences the contaminant. Water plays a very significant role in contaminant behavior; consequently, contaminant behavior is much different in ground water systems than in surface water systems like lakes, streams, ponds and reservoirs.

Ideas Taught: Contaminant movement is strongly influenced by water movement; contaminant characteristics also significantly affect contaminant behavior.

Materials Needed:

Procedure:

1. ___ Before the class meets, fill five bowls to within about 1/2 inch of the top with tap water (about 70 degrees or so - not too hot, and not too cold). Set the bowls on a table or desk and allow them to set there long enough for the water to become quite still.
2. ___ Place a piece of filter paper or a coffee filter in each of five funnels and lightly moisten to keep the filter papers in place.
3. ___ Place each funnel in the top of a clean jar.
4. ___ When the class has assembled, ask the students to identify each of the different contaminants you have (vegetable oil, vinegar, corn starch, sugar or salt, and pepper). Each substance
5. represents a different type or form of contaminant.
___ If the students do not guess, tell them what they are.
6. ___ Explain to the students that you are going to illustrate how things mix and move in water.
7. ___ Slowly pour a contaminant into a bowl. Avoid pouring too fast, to reduce the amount of disturbance and movement of the water. A good one to start with is the oil - since it does not mix with the water.
8. ___ After a moment or two, use a plastic spoon to mix the water vigorously, stirring the water near the outer edges of the bowl.
9. ___ Ask the students to again watch and observe what happens and why. They should see that the oil disperses (breaks into smaller droplets), but does not mix with the water. The oil has a density different from the water and chemical and electrical properties which discourage it from mixing readily with water.
10. ___ Repeat the process with the vinegar - first slowly pouring and then mixing. You should see a different response. The vinegar is a different kind of chemical with different behavior. It readily mixes with the water and loses its identity - even with little mixing of the water.
11. ___ Repeat the process with corn starch. Initially, the corn starch will hang together in a lump. It will stay that way almost indefinitely if the water is not mixed. The corn starch particles are very fine and adhere or stick together very strongly.
12. ___ What happens when you mix and stir the water? You need to mix vigorously to get the corn starch to break up and even then, it takes much effort. Ask the students what happened to the corn starch. Actually, it never did mix with the water. It just spread out and got stirred in. However, the corn starch is a very fine particle (much like clay material in soil). It can be dispersed and spread out, but it will not dissolve.
13. ___ Repeat the process with the sugar or salt, first slowly pouring the sugar or salt into the water. Without mixing, the sugar or salt will stay in something of a pile at the bottom of the bowl for quite a while. When you start mixing, however, the material will dissolve completely.
14. ___ Compare the sugar or salt exercise with the corn starch.
15. ___ Finally, repeat the exercise with the pepper. You will see the pepper immediately disperse when poured into the water. It does not hang together like the corn starch. Neither does it dissolve like the sugar nor salt.
16. ___ Mix the water with pepper in it. You will see that the color of the water has changed. Here is an example of something which both disperses and dissolves, but it does not do either one completely.
17. ___ After you have mixed all five contaminants, let the students take another look and discuss what has happened. Talk about the similarities in the five, the differences, and why they did what they did. Also be sure to mention the effect of mixing. What happens if you do not mix versus if you do mix? You can see that with some contaminants, water movement has little effect. With others, water movement accelerates the mixing and dispersion process. With some contaminants, the mixing and movement causes the contaminant to dissolve and lose its identity; while with some contaminants, the mixing and movement merely causes dispersion.
18. ___ Now pour each bowl of water through a funnel with filter paper.
19. ___ When the drainage has stopped, look at what remains on the filter paper (spread the paper out on a paper plate to get the full effect). Look at and compare the drainage water.