Lesson 3 - Page 6


PROBLEM: Why should you test for pH, nitrates, and dissolved oxygen?


MATERIALS: thermometer, La Motte test kits for pH, nitrate, and dissolved oxygen, water samples

PROCEDURE: Use only with LaMotte kits and materials

pH Testing Procedure

1. Rinse each test tube with the water sample. Gloves should be worn to avoid skin contact with the water.

2. Fill the tube to the 5mL line with sample water.

3. While holding a dropper bottle vertically, add 10 drops of Wide Range Indicator Solution.

4. Cap and invert several times to mix.

5. Insert the tube into the Wide Range pH Comparator. Hold the comparator up to a light source. Match the sample color to a color standard.

6. Record the pH value.

7. Wash your hands

Nitrate Testing Procedure

1. Fill the sample bottle with sample water. Use gloves if drawing the sample by hand.

2. Rinse and fill one test tube to the 2.5 mL line with water from the sample bottle.

3. Dilute to the 5 mL line with the Mixed Acid Reagent. Cap and mix. Wait 2 minutes.

4. Use the 0.1 g spoon to add one level measure (avoid any 50-60 times in one minute). Wait 10 minutes.

5. Insert the test tube into the Nitrate Nitrogen Comparator. Match the sample color to a color standard. Record the result as mg/L(ppm) Nitrate Nitrogen (NO3-N). To convert to mg/Nitrate (NO3) multiply by 4.4.

6. Place the reacted sample in a clearly marked container. Arrangements should be made with toxic material handlers for safe disposal. Please wash your hands after this water test is completed.

Dissolved Oxygen Testing Procedure

1. If you have a barometer, record the atmospheric pressure. Remove the cap and immerse the DO bottle beneath the riverís surface. Use gloves to avoid contact with the river.

2. Allow the water to overflow for two to three minutes (This will ensure the elimination of bubbles).

3. Make sure no air bubbles are present when you take the bottle from the river.

4. Add 8 drops of Manganous Sulfate Solution and 8 drops of Alkaline Potassium Iodide Azide.

5. Cap the bottle, making sure no air is trapped inside, and invert repeatedly to fully mix. Be very careful not to splash the chemical-laden water. Wash your hands if you contact this water. If oxygen is present in the sample, a brownish-orange precipitate will form (floc). The first two reagents "fix" the available oxygen.

6. Allow the sample to stand until the precipitate settles halfway. When the top half of the sample turn clear, shake again, and wait for the same changes.

7. Add 8 drops of Sulfuric Acid 1:1 Reagent. Cap and invert repeatedly until the reagent and the precipitate have dissolved. A clear yellow to brown-orange color will develop depending on the oxygen content of the sample.

8. Fill the titration tube to the 20 mL line with the "fixed": sample and cap.

9. Fill the Direct Reading Titrator with Sodium Thiosulfate 0.025 N Reagent. Insert the Titrator into the center hole of the titration tube cap. While gently swirling the tube, slowly press the plunger to titrate until the yellow-brown color is reduced to a very faint yellow.

If the color of the fixed sample is already a faint yellow, skip to step 10.

10. Remove the cap and Tritrator. Be careful not to disturb the Titrator plunger, as the tiration begun in step 8 will continue in step 11. Add 8 drops of Starch Indicator Solution. The sample should turn blue.

11. Replace the cap and Titrator. Continue titrating until the sample changes from blue to a colorless solution. Read the test result where the plunger top meets the scale. Record as mg/L (ppm) dissolved oxygen.




Sample #


dissolved O2












Describe conditions:

Describe water:



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