Environmental Chemistry
Solution Conductivity and Total Dissolved Solids (TDS)
Purpose:
- 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
conductivity.

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
compounds.
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–