Test+5+-+Dissolved+Solids

**﻿Dissolved Oxygen!**

Dissolved oxygen is a relative measure of the amount of oxygen that is dissolved or carried in a given medium. It can be measured with a dissolved oxygen probe such as an oxygen sensor or an optode in liquid media, usually water. Oxygen is important to measure because animals, such as fish need oxygen to live. As water moves past their gills oxygen gas in the water, called dissolved oxygen are transferred from the water to their blood. Oxygen is produced during photosynthesis in the daylight hours. But during the night, concentrations steadily decline and they are lowest just before dawn, when photosynthesis resumes. During the summer months when stream water is warm, oxygen can be limited because it cannot “soak up" more oxygen gas, unlike when it’s cold it can. Pollution is another factor that changes the oxygen.



**How To Measure Dissolved Oxygen!** **Step 1.** Fill the bottle to the marked line with the water sample so that it won't contain any air when it's stoppered. Add two ml of manganese sulfate just beneath the surface of the water with the calibrated pipette. Then, add two ml of alkali-iodide-azide. **Step 2.** Stopper the bottle carefully so that it has no air remaining in it. Turn the bottle upside-down a few times to mix the reagents and check for air bubbles. If there are any, discard the sample and begin the procedure again. **Step 3.** Add two ml sulfuric acid with the pipette held above the surface of the water. Replace the stopper and mix the sulfuric acid so that it dissolves the precipitate, or sediment, by inverting the bottle a few times. **Step 4.** Draw off 201 ml of the water sample and slowly add sodium thiosulfate with the pipette while stirring the sample. Continue adding sodium thiosulfate until the sample becomes a pale straw color, noting the number of ml used. Add two ml of the starch solution and wait for the sample to turn blue. **Step 5.** Resume adding sodium thiosulfate one drop at a time while stirring until the sample becomes clear. The concentration of dissolved oxygen in the sample in milligrams per liter will be the total number of milliliters of sodium thiosulfate added.

** ﻿ At what level of dissolved oxygen is it healthy ﻿ ?** DO levels in rivers that are at a 90% saturation level or higher consistently are considered healthy.

=﻿I tested the dissolved oxygen! = ﻿First I calibrated the dissolved oxygen probe. 1. Place the tip of the probe into the sodium sulfite calibration solution 2. Then add tap water into the bottle 1/4 inch. <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">My results- The calibration came to 0 <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;"> The tap water came to 8.8 <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">Now I collected data of the dissolved oxygen in our stream. <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">1. Place the tip of the probe into the stream and stir it slowly <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">My results- The amount of dissolved oxygen in our stream came to 13.5. <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;"> **<span style="color: #ff006e; font-family: 'Times New Roman',Times,serif;">Therefore, our amount of dissolved oxygen in our stream is perfect! **