Forensics C

[SOninja]

quick word of advice... the B div science crime buster site on soinc.org has water testing stuff,
though it might not be exactly what you need, it's pretty useful and it can get you started

[gsingh2011]

I checked the crime busters thing, but it really wasn't what I was looking for.

honestly, the best way to learn to test water is to actually do it.

I can't do it if I don't know where to start. Actually, I know how to do everything except the cation and anion tests. On my regional test we had to test for chloride ions, and I had no idea what to do.

[austinwu]

I'm having quite a hard time with the common ions as well, but maybe it has to do with reacting the free ions with solutions that are provided to you, and then looking for the precipitate?
Also, I was wondering if anyone knows about what, and how to test for turbidity, DO, BOD, and COD?

[abhas]

I highly doubt that they are going to ask us to test for BOD because it takes a minimum of 3 days to test for that. They might just give us data and ask us to analyze it. DO, I am not so sure about. Turbidity is pretty basic. You take the water in a vial and use a black and white colored wheel and check for floating particles.

about the cation and anion tests.....the precipitate is the best way to go about some of the ions. maybe not all of them.

[kjhsscioly]

DO is a simple probe, and it is required that they give us the instructions on working it

[wexs883198215]

Any tips on telling the difference between KCl and NaCl? I struggle to see the lavender flame of KCl sometimes, and I would like to have a better way of differentiating the two.

[gogofofo]

Any tips on telling the difference between KCl and NaCl? I struggle to see the lavender flame of KCl sometimes, and I would like to have a better way of differentiating the two.

NaCl's flame is unmistakably yellow, at that point it's a matter of differentiating it from the other Na compounds.

[jazzy009]

Any tips on telling the difference between KCl and NaCl? I struggle to see the lavender flame of KCl sometimes, and I would like to have a better way of differentiating the two.

NaCl's flame is unmistakably yellow, at that point it's a matter of differentiating it from the other Na compounds.

...probably not what you want to hear, but if you can't see the lavender flame, you need to relearn flame tests. No offense. It takes a second for the lavender to appear, but once it does it's pretty obvious. As oppose to any sodium compound as gogo pointed out is yellow and stains your loop...argh.

[AustinRHL]

Yeah, loop staining is a major problem for us. We've had to adapt our flowchart because our loops no longer can distinguish between sodium and any of the ones that don't burn, and some of our loops have become permanently colored. Lithium did so particularly badly, and I think that boric acid gets "fused" onto the loop, as well.

We've all been scratching our heads at the water testing portion of the event. We aren't worried about it - it should be straightforward - but we can't fathom how it can replace such essentials as hair and fibers. After all, the event name is Forensics, not Chemical Testing, so what were the event designers thinking?

I've only done Forensics at the national level once before, and as I'm sure that any veterans of the event will remember, the test was absurdly long (I recall multiple hundreds of questions). Is that how the event is always run at nationals, and can we expect it do be the same this year?

[jazzy009]

Yeah, loop staining is a major problem for us. We've had to adapt our flowchart because our loops no longer can distinguish between sodium and any of the ones that don't burn, and some of our loops have become permanently colored. Lithium did so particularly badly, and I think that boric acid gets "fused" onto the loop, as well.

We've all been scratching our heads at the water testing portion of the event. We aren't worried about it - it should be straightforward - but we can't fathom how it can replace such essentials as hair and fibers. After all, the event name is Forensics, not Chemical Testing, so what were the event designers thinking?

I've only done Forensics at the national level once before, and as I'm sure that any veterans of the event will remember, the test was absurdly long (I recall multiple hundreds of questions). Is that how the event is always run at nationals, and can we expect it do be the same this year?

Use hydrochloric acid. Even a diluted amount will get rid of the stains.

As for the length of test, the person who writes the Nats test suggests to people writing tests something along the lines of this:
Invitationals: 100 points
Regions: 200 points
State/Nats: 300-400 points
She claims that this will separate the teams adequately without having too many ties. Sound logic, I suppose.