Chemical Parameters
Title: Chemical Parameters
Essential Question: How can chemical tests help determine the quality of water in streams?
Materials: Water test kits – Dissolved Oxygen, pH, (turbidity, alkalinity, chloride if available).
Conductivity Meter, thermometer. LaMotte test kit directions are given at the end of this lesson.
Other sources of test kits are available too.
Water Samples – local creek if possible, pond water, rain water, tap water – various sources
Engage
Begin by asking if anyone has ever done any water testing - maybe for a swimming pool. What
was being tested? How was the test conducted?
Explain that we will be testing water for various physical and chemical parameters that will give
a picture of the ability of the water to support living organisms. Those tests include the
temperature, pH, conductivity and dissolved oxygen (and might include others such as turbidity,
alkalinity and chloride).
Explore / Explain
The teacher in formation page contains additional information about each of these tests. Be sure
to utilize it as needed. Not all of these tests need to be done, but the big four are temperature,
pH, conductivity and dissolved oxygen.
The directions for each test are in the kits or on the direction page at the end of this lesson plan.
Temperature – is taken of the air and water. In cold weather the air is usually colder than the
water and vice versa. Water temperature is important for other parameters. Gases dissolve
better at lower temperatures, solids usually dissolve better at higher temperatures. Many
organisms have an optimal range of temperatures in which they live.
Turbidity – measures suspended solids in the water. A visual recording often is sufficient – is it
clear, cloudy, muddy, etc.
Conductivity – using a conductivity meter will give an indication of dissolved salts in the water.
It is not specific, just total dissolved ions.
Conductivity can be demonstrated with distilled water (should be zero), tap water (in the
hundreds) and a pinch of salt added to water (thousands).
pH – measures if the water is acidic or basic. Natural waters should be close to neutral (around 7
on the pH scale). Many organisms have an optimal range of pH in which they live too.
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Chemical Parameters
pH can be tested on various sample – tap water, rain water, pinch of baking soda added to water,
or drop or two of vinegar added to water.
Dissolved Oxygen – measures the amount of dissolved oxygen in the water. Aquatic organisms
breathe oxygen dissolved in the water – not the oxygen in the water molecule.
Dissolved oxygen can be conducted on any water samples – shake it up first if you want to
ensure some dissolved oxygen. In streams, oxygen is mixed with water where it tumbles over
rocks – the riffle areas of streams.
Other Tests - Other tests could be alkalinity (the buffering capacity of the water) and chloride.
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Chemical Parameters
Directions for pH, Dissolved Oxygen and Conductivity
LaMotte Test Kits
pH Test
Fill tube to line and add 10 drops of indicator. Mix and compare to colorimeter. Numbers are
associated with each color and estimates between numbers can be made if
Dissolved Oxygen Test
Fill DO bottle by opening under water and letting the water bubble in. Close under water.
*Add 8 drops of the following: Manganese Sulfate and Alkaline Potassium Iodide. Cap and mix
slowly.
(should be a brown gel-like solid present)
*Add 8 drops of Sulfuric Acid. Cap and mix again. (solid dissolves – left with an amber colored
liquid)
*Pour from the bottle into the test vial to the 20 mL line.
*Fill the syringe (titrator) carefully to avoid air bubbles from the bottle marked Thiosulfate.
*Place the titrator in the hole in the cap of the vial and add a drop at a time with swirling to mix.
When the solution changes to a light yellow, STOP.
*Add 8 drops of starch indicator to the vial.
*Continue titration a drop at a time. When the color changes from blue-black to clear STOP and
read the amount of Dissolved Oxygen in parts per million (ppm) from the titrator.
Conductivity and Temperature
*Conductivity is measured by turning on the device and letting it stabilize at “0” and then
placing the end in the water. Read the Temperature and Conductivity on the meter.
(if the meter has no thermometer function, use the thermometer to record the water temperature)
*Record the Air Temperature too.
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