by Naomi White, Science Teacher, Jefferson High School, LAUSD

LESSSON SHEET

[ Student Handout ]

Time Frame: one period

Concept:
Turbidity is the amount of muddiness or cloudiness in the water usually caused by stirring up of sediments. Turbidity affects the amount of sunlight reaching aquatic plants and therefore affects the entire aquatic food chain by affecting the amount of oxygen available. Oxygen content of aquatic ecosystems is perhaps the single most important factor in the ecological health. Lower oxygen reduces biodiversity. Many factors including turbidity, affects oxygen content. These include eutrophication caused by unnaturally high nutrient levels, temperature, plant growth, surface area.

Objective:
Students will conduct a test to determine the turbidity of water samples.

Materials:

LaMotte Turbidity test kit (price: $5.50/call: Frey 1-888-222-1332/kit#: F22366)

Preparation:
Collect a water sample from a local body of water. This turbidity test will not work unless the water is fairly turbid. Accurate laboratory turbidometers are too expensive for most secondary school science budgets. Therefore if the water sample is not turbid enough, "create" a sample by adding a little cornstarch to the water. If you do this do not telecommunicate your turbidity data. The lab will only serve to introduce the concept of turbidity.

Procedure:

1. Fill one of the tubes with the water sample to the 50 ml mark.
   
2. Fill the second tube with tap water to the 50 ml mark.
   
3. Looking down into the tubes from the top, compare the black dots on the bottom of the tube (if one cannot be seen, only fill each tube to the 25 ml mark).
   
4. Using the eye dropper, add the standard turbidity reagent .5ml at a time, until the dots appear the same. Record the amount of reagent used.
   
5. Each milliliter of reagent equals 10 Jackson Turbidity Units (JTU's) if the 50 ml line was used. Each milliliter equals 20 JTU's if the 25 ml line was used. Use the enclosed chart if you need more help calculating the JTU's.