Our new Turbidity Sensor is extremely useful in water quality studies and other experiments where the clarity of a solution is to be measured. Its small, sleek design, and simple setup make it easy to use at a water quality study site or back in the classroom. Chemistry and biology teachers can use this sensor to monitor precipitates formation or algae and yeast populations. The Turbidity Sensor measures turbidity in NTU (the standard unit used by most water collection agencies and organizations). Calibration can be done very quickly and easily using the high quality Hach StablCal ® 100-NTU standard (included). Also included is a high-grade glass cuvette for the water sample to be measured.
(Order Code TRB-BTA, $99)

While attending the T^{3 TM} (Teachers Teaching with Technology^TM) Environmental Institute pilot held in Jackson, Michigan this summer, I saw this interesting lab activity presented by Rick Piercy (Yucaipa HS, CA). In this inquiry-based activity, students design a filtration system from common materials, such as sand, charcoal, filter paper, and cotton. Students then take a sample of water contaminated with grass clippings, vinegar, coffee grounds, and table salt, and test it for turbidity, total dissolved solids, pH, and clarity. After their initial test, the sample is poured through the filter system. The filtrate is collected in a 400-mL beaker and tested once again to determine how effective the system is at filtering out the contaminants.

The turbidity of the solution is measured using the Vernier Turbidity Sensor. Total dissolved solids (TDS) can be measured with the Conductivity Probe and the solution’s pH can be checked with the pH Sensor. To build a filtration device, you will need the following: a 1-liter plastic bottle, charcoal, cotton balls, filter paper, sand, and baking soda (sodium bicarbonate). To prepare the test water, mix the following together in a 1-gallon container: water, grass clippings, potting soil or dirt, 10-100 mL of vinegar, 1-5 g table salt, and coffee grounds.

Students find that their pH has changed from an acidic value of 4-5 (due to vinegar) to a neutral or slightly basic value of 7.5-8.0. The turbidity values will significantly decrease after the first filtering, then slightly drop following the second. The filter mechanism is unable to remove ions, so expect to see no change in TDS, or an increase due to the addition of sodium bicarbonate to the filter.

	Turbidity (NTU)	pH	Total dissolved solids (mg/L)
Initial reading	135	5.3	1240
First filtering	64	7.9	4450
Second filtering	50	8.1	4690

This activity is a great way to use sensors in an inquiry-based setting. Once your students have tested their filtration device, have them use each of the filter materials separately to determine how each material affects the water sample.