1
Q
What is measured during a DO test?
A
The level of free, dissolved oxygen
2
Q
Average level of DO in natural waters
A
7-9 mg/L
3
Q
What is the Winkler Method?
A
A way to measure DO based on the tendency of free oxygen to attach to certain ions. Sometimes called iodometric procedure.
4
Q
What is the azide modification?
A
This modification to the winkler method eliminates the interference of nitrites
5
Q
Chemicals and order used in Winkler DO
A
- Manganous sulfate
- Alkaline-iodide-azide
- Concentrated sulfuric acid
- Starch Solution
- 0.025N sodium thiosulfate
6
Q
Winkler DO procedure
A
- Fill buret with 0.025N sodium thiosulfate
- Collect a sample in a 300mL DO bottle minimizing agitation. Place stopper.
- Pipet 1mL of Manganous Sulfate into bottle below liquid surface. Replace stopper.
- Pipet 1mL of alkaline-iodide-azide into bottle
- Replace stopper and invert bottle about 20x
- Let settle until sediment is about halfway down
- Invert again 20x. Let settle until halfway down
- Remove stopper and pipet 1mL sulfuric acid into bottle.
- Replace stopper and invert 20x
- Measure 201 mL of sample into graduated cylinder
- Pour contents of graduated cylinder into 500mL Erlenmeyer flask
- Titrate sample to straw yellow color.
- Add about 1ml of starch solution for blue color
- Titrate slowly until sample becomes colorless.
7
Q
What will occur if there is no DO?
A
sample with turn white
8
Q
What is the effect of water temperature on DO?
A
Colder water is able to hold more DO
