The dissolved oxygen protocol is the sixth in a series of eight hydrology protocols:

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Junior High and Up Estimated Time: 5 Minutes

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The purpose of the Electrical Conductivity protocol is to measure the amount of total dissolved solids in the water. The conductivity of a water sample is the measure of its ability to carry an electric current and the more dissolved solids in the water, the greater its electrical conductivity. In order to measure the amount of total dissolved solids, students must first determine the conductivity of the water sample and then multiply that number by .67. The formula for this equation goes as follows: Total Dissolved Solids (PPM) = Conductivity (microSiemens/cm) x .67. MicroSiemens/cm is the metric unit of measurement for conductivity Step 1 - Calibration Before measuring the conductivity of a water sample, students must first calibrate the conductivity meter they will use on the water sample. In order to calibrate, students must measure a standard solution with the conductivity meter. Students must first press the ON/OFF button to turn the tester on. The students must rinse the electrode at the bottom of the meter with distilled water from a squeeze bottle and afterwards blot it dry with a tissue. If the display on the conductivity meter does not read the standard value, students must adjust the instrument with a small screw. The standard solution must be compared with the water sample protocol. Step 2 - Conductivity Measurment Students must first repeat the motions used to calibrate the conductivity meter. First students will remove the cap from the meter and press the ON/OFF button. Afterwards students must rinse the electrode with distilled water and blot it dry. Once students have completed these procedures they can immerse the meter in the water sample and gently stir the sample for a few seconds to allow the display value to stabilize. Students may then read the display value and record it.

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Total dissolved solids tester (or conductivity tester) Standard solution Distilled water Squeeze bottle Soft tissue Three 50 mL or 100 mL beakers Jewelry screwdriver for calibration

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1) The standard solutions are ready for calibration. 2) The student uses the conductivity meter to measure the conductivity of the standard solution. 3) The student uses the screw to adjust the conductivity meter. 4) A student tests the conductivity of the water by measuring the total dissolved solids present in the sample.

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