Quality Assessment: Chemical: Conductivity and Density
To "see" the electrical current being carried by Na+ and Cl- ions, try the following activity. First, connect the positive terminal of a battery to an electrode. Place the electrode in a glass of deionized water. Next, connect the negative terminal of the battery to a light bulb, then connect the light bulb to an electrode. Place the electrode in a glass of deionized water (see animation below). Notice that the light bulb does not glow. Add some salt (NaCl) to the deionized water (see animation below). Notice that the light bulb starts to glow. That is because the Na+ and Cl- ions complete the circuit between the positive and negative electrodes. They enable the electrical current to flow through the circuit.
Like conductivity, water density is an indicator of the physical presence of chemicals in water. The density of water is related to salt content and water temperature. This is a very useful parameter to measure because the salinity of a body of water is one of the main factors determining what organisms will be found there.
/ Alkalinity / Hardness
/ Nitrates. Nitrites, and Ammonia / Ortho-
and Total Phosphate / Dissolved Oxygen and
Biochemical Oxygen Demand / Fecal Coliform
/ Conductivity and Density
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