Forensics C

[salcedam]

Both magnesium sulfate and calcium nitrate form a precipitate with NaOH. The only way to tell them apart at that point is the flame test. If there was no color, then it's magnesium sulfate. If there was a striking orange flame color, it's calcium nitrate.

[Phenylethylamine]

Both magnesium sulfate and calcium nitrate form a precipitate with NaOH. The only way to tell them apart at that point is the flame test. If there was no color, then it's magnesium sulfate. If there was a striking orange flame color, it's calcium nitrate.

You're right, my previous post was incorrect. Calcium hydroxide is much more soluble than magnesium hydroxide, but it will still form a visible white precipitate. I suppose that calcium nitrate + sodium hydroxide might precipitate less readily/require more NaOH to form the same amount of precipitate, but this would be subjective and very hard to judge (particularly given that you're unlikely to have them next to each other in competition).

Does anyone have a good way to tell the difference between MgSO4 and Ca(NO3)2 besides the flame test.

Magnesium sulfate forms a white precipitate with NaOH (so dissolve some of the powder in water in your well plate, and put a couple drops of NaOH in there. If it's magnesium sulfate, you'll immediately see a pretty unmistakable white precipitate form; if it's calcium nitrate, nothing).

isn't mgso4 soluble in water and ca(no3)2 not.... if not i feel REALLY stupid....

Both are soluble in water. All nitrates and most sulfates are soluble in water.

[Steelfoam]

Okay, so I am trying to put a flowchart of plastics together. I want to know whether they will sink or float in saturated NaCl and isopropyl alcohol. However, it seems that there is no set solution (I don't see in the rules that they will always give you, for example, 10% NaCl). Are they any suggestions for what I should do so I can still test and have some idea of what they will do?

I would go ahead and put it your flowchart with the 10% and isopropyl, at the competition they will probably give the densities of the liquids you test with. Although you won't know the liquids in advance, just having chart might give you a general idea of the densities in relation to each other and they competition liquids shouldn't be too far off from densities of the liquids in your flowchart.

[computergeek3]

Does anyone know a way to definitely tell the width/length of a blood splatter apart? I know it seems like a stupid question, but I got a question on a test that had me confused for a bit about width vs. length

[Dragonshark]

Does anyone know a way to definitely tell the width/length of a blood splatter apart? I know it seems like a stupid question, but I got a question on a test that had me confused for a bit about width vs. length

The longer dimension of the spatter is the length (I think).

[AlphaTauri]

Does anyone know a way to definitely tell the width/length of a blood splatter apart? I know it seems like a stupid question, but I got a question on a test that had me confused for a bit about width vs. length

The longer dimension of the spatter is the length (I think).

Correct. (If you switch up the numbers for length and width it will give you an error when you put it into the arcsin(width/length) equation, so that's a nice check!)

[JustDroobles]

How do you calculate the velocity of blood from it's splatter? Or is it only possible to classify it as high, medium, or low velocity?

[computergeek3]

How do you calculate the velocity of blood from it's splatter? Or is it only possible to classify it as high, medium, or low velocity?

pretty sure that's the only way...I have never had anything aside from high medium or low, and i'm pretty sure any other way would just be a surefire method of losing time

[computergeek3]

does anyone know how to read a mass spec graph? I am hopelessly confused on this...

[csiguy55]

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