Conductivity and TDS Lab Notes

Environmental Chemistry
Solution Conductivity and Total Dissolved Solids (TDS)
- To use a linear calibration curve to determine the concentration of Total
Dissolved Solids (TDS) in a sample of stream water.
Prelab Notes:
Impurities in water samples are usually found in two forms; suspended and dissolved.
Suspended impurities can be filtered out and affect the turbidity of the water sample.
Dissolved impurities pass right through filter paper and affect the solutions
TDS or total dissolved solids is a measure of
the total concentration of dissolved substances
in a water sample.
These dissolved substances are usually ionic
Ionic Compounds – Consist of
positive and negative ions in a
crystal lattice structure. When
water is introduced into this
structure, the ions break out of it
and “dissolve.”
A high TDS concentration does not necessarily
mean that a sample is “polluted” or dangerous.
These ions come from a variety of sources.
Sources of Total Dissolved Solids
 Hard-Water Ions
- Ca2+
- Mg2+
- HCO3–
 Fertilizer in agricultural runoff
- NH4+
- NO3–
- PO43–
- SO42–
 Urban runoff
- Na+
- Cl–
 Salinity from tidal mixing, minerals, or
returned irrigation water
- Na+
- K+
- Cl–
 Acidic rainfall
- H+
- NO3–
- SO32–, SO42–