Solids are found in bodies of water in two forms, suspended and dissolved. Suspended solids include silt, stirred-up bottom sediment, decaying plant matter, or sewage-treatment effluent. Dissolved solids are ions introduced to water from salts, acids, bases, hard-water minerals, or soluble gases that ionize in solution. Suspended solids will not pass through a filter, whereas dissolved solids will.
In this experiment, you will measure the total dissolved solids (TDS) of several water samples using a Vernier Conductivity Probe. You will learn to convert conductivity values in mS/cm to TDS values in mg/L. The Conductivity Probe can determine the ability of dissolved salts and their resulting ions to conduct an electrical current. The test described here will not tell you the specific ion responsible for the increase or decrease in TDS. It will simply give a general indication of the level of dissolved solids in the water sample.
In this experiment, you will
Use a computer and an NXT to measure total dissolved solids.
Learn to use a conversion factor.
Compare water from different sources.
Sensors and Equipment
This project/activity requires each of the following Vernier sensors and equipment (unless otherwise noted):