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I'm the youth ed manager at Denver Water in Colorado. We do a water treatment demo in the classroom, and currently we use the first part of the Winkler DO test to create floc. I'm looking for a better demo that creates white floc and doesn't turn the water brown. I've tried using alum and mixing it with alkaline iodide azide reagent. It creates wonderful, white floc. What I don't know is if it's safe in a classroom setting. Can you help?

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    $\begingroup$ alkaline iodide azide reagent is strongly basic. No worse than Drano which is a commercial product in grocery stores. But it certainly isn't something that I'd want to spill on a kid. Could you just ppt CaCO3 by using CaCl2 and NaHCO3? $\endgroup$ – MaxW Feb 6 '17 at 19:15
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    $\begingroup$ How about curdling milk with lemon juice or vinegar? Milk goes through coffee filter and you get zilch. Curdle milk then you get the curds on filter. Bonus is that this is something that the kids can do at home. // Learned that the hard way. Tried to be nice to my wife once and cut up a kiwi in her cereal. The acid in the kiwi curdled the milk -- yuck! $\endgroup$ – MaxW Feb 6 '17 at 19:35
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    $\begingroup$ Have you assessed the SDS for these materials? Alkaline iodide azide is approx 50% hydroxide, so extremely caustic. Not familiar with the Winkler test, but it appears that it involves lots of KOH also. What risk assessment and safety data have you got for this test in the classroom? $\endgroup$ – long Feb 6 '17 at 20:50
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    $\begingroup$ @MaxW, another old dog here. I've just learned in the past few months that an MSDS is now called an SDS, though they are the same thing. They did it to simplify things LOL. Take a look here. $\endgroup$ – airhuff Feb 7 '17 at 5:47
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    $\begingroup$ Geeze, I thought SDS was Students for a Democratic Society ;-) $\endgroup$ – MaxW Feb 7 '17 at 5:59

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