If you drop the contents into the water they will come in contact with the air and this will introduce oxygen into the sample and alter results. If any air bubbles occur, then the sample is contaminated and you will need to start over.
If oxygen is present you will observe the formation of floc. This is an orange-ish solid that will settle in the bottom of the flask.
Wear gloves and goggles for safety when working with sulfuring acid. Avoid contact with skin and eyes. Do not ingest. Do not inhale.
Write down the initial amount of sodium thiosulfate in the pipet. Stir the solution continually as you titrate.
Starch solution can be made by mixing water with corn or potato starch, or you can buy one premade.
Hold the sample up against a white background in order to look for blue color.
For example, if you used 8 mL of sodium thiosulfate, that would correspond to a dissolved oxygen content of 8 mg/L.
All meters are calibrated differently. See the manufacturer’s instructions for variations that are specific to your meter. Meters are calibrated in Celsius not Fahrenheit.
Indigo carmine will produce a deep blue color. Rhodazine D will produce a deep pink color.
