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Lab #3: Dissolved Oxygen and Reactive Phosphate

Joe Conroy

13/14 April 2004

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Goals

1) Determine the dissolved oxygen concentration and % saturation for three different sources

2) Determine the soluble reactive phosphorus concentration for three sources

3) Practice good analytical technique

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Winkler Titration

After adding manganous sulfate and sodium iodide/sodium hydroxide

solutions, the amount of oxygen in the sample is proportional to the amount of manganese precipitated to form a

manganous hydroxide “floc”

Once the concentrated sulfuric acid is added, the amount of iodine released into solution is proportional to the amount of

oxygen in the original sample

Determine the amount of iodine released by titrating with sodium thiosulfate

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Winkler Titration

While many people do Winkler titrations. . .

So do TA’s!

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Dissolved Oxygen Concentration

• Winkler Titration

• Methods in lab handout, pp. 115-117

• Record data on page 119

• Chemicals are hazardous – BE CAREFUL!!!

• Titrate from orange to very light yellow, then add starch (turns blue) titrate until just clear

• DO Meter

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Soluble Reactive Phosphorus

• Measure phosphorus concentration using spectrophotometry

• Amount of P proportional to the color change

• More Blue = More P

• Measure turbidity (particulates that absorb)

• Use calibration curve using standards

• Methods on p. 120; Record data on p. 121

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Consequential Questions

• How do biota impact dissolved oxygen concentration?

• How do biota impact phosphate concentration?

• What biotic processes impact both simultaneously?