Forensics C

[scm424]

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).

Wait Calcium Nitrate DOESNT react with NaOH? I thought it did. Did you try it? because im pretty sure someone told me or i tried it at some point and it did react. Not sure though.

Calcium nitrate is soluble (all nitrates are soluble), sodium hydroxide is soluble (it's a strong base, so it dissociates completely). A double replacement reaction doesn't occur because none of the products are insoluble (nothing changes). When the solutions are mixed, it's basically just a puddle of Ca2+, NO3-, Na+, and OH- ions.

Magnesium sulfate, on the other hand does react with sodium hydroxide. This is because magnesium hydroxide (formed in the double replacement reaction) is insoluble. The only soluble hydroxides are the strong bases.

[claribassist13]

Hey everyone.
So my partner and I are getting ready for our events next week, and I am trying to put together a spreadsheet for powders and plastics. Naturally, I have a few questions.

Powders
Is glucose the only thing that reacts with Benedict's solution?
What reacts with HCl and NaOH?
Is cornstarch the only thing that reacts to iodine?
Anything else I should know?

Plastics
I have the densities for a few plastics in straight water. Are there other solutions that I should have their densities in?

Thanks for all the help!

[knittingfrenzy18]

Hi there from a Div B Food Scientest:

I can answer some of your questions

Benedict's Solution will reduce anything with a free aldehyde, ie reducing sugars.
Rule of thumb: All monosaccharides are reducing, but not all reducing sugars are monosaccharides. Some disaccharides will reduce, but not sucrose. Keep that one in mind.

I think that HCl and NaOH are an acid and base that react with eachother to form NaCl(sodium chloride) and water, H2O.

Iodine will test positive with anything that has a significant amount of starch in it, not just cornstarch.

[AlphaTauri]

As knittingfrenzy18 said, glucose but not sucrose will react with Benedict's - it will turn orange-ish when heated and left to sit for a little while. However ammonium chloride will also react to form a blue-purple color with Benedict's and KCl may or may not turn green when heated (there was a discussion on this a few pages back; you should probably read through that since I can't recall exactly what we established reaction-wise for KCl and its cousin LiCl).

Anything with a carbonate in it (CO3) will react with HCl.
Magnesium sulfate will apparently form a precipitate with NaOH; ammonium chloride also apparently reacts to produce some sort of ammonia gas (be careful if you're testing this one).

Cornstarch is the only powder on the list that will react with iodine.

Besides that, flame tests are really good to distinguish between a few powders that have very distinctive flame colors or other burn patterns (plus, it's just plain fun to turn the flame different colors).

You can find most of the densities for plastics online. Some common density solutions are: saturated NaCl, 10% NaCl, plain water, 46% isopropyl alcohol, and vegetable oil.

[claribassist13]

Hi there from a Div B Food Scientest:

I can answer some of your questions

Benedict's Solution will reduce anything with a free aldehyde, ie reducing sugars.
Rule of thumb: All monosaccharides are reducing, but not all reducing sugars are monosaccharides. Some disaccharides will reduce, but not sucrose. Keep that one in mind.

I think that HCl and NaOH are an acid and base that react with eachother to form NaCl(sodium chloride) and water, H2O.

Iodine will test positive with anything that has a significant amount of starch in it, not just cornstarch.

Thanks for the help, although I didn't mean what do HCl and NaOH react to make. I meant what powders react with them. I am testing them tomorrow though, so it's all good. Thanks for the help though!

[claribassist13]

As knittingfrenzy18 said, glucose but not sucrose will react with Benedict's - it will turn orange-ish when heated and left to sit for a little while. However ammonium chloride will also react to form a blue-purple color with Benedict's and KCl may or may not turn green when heated (there was a discussion on this a few pages back; you should probably read through that since I can't recall exactly what we established reaction-wise for KCl and its cousin LiCl).

Anything with a carbonate in it (CO3) will react with HCl.
Magnesium sulfate will apparently form a precipitate with NaOH; ammonium chloride also apparently reacts to produce some sort of ammonia gas (be careful if you're testing this one).

Cornstarch is the only powder on the list that will react with iodine.

Besides that, flame tests are really good to distinguish between a few powders that have very distinctive flame colors or other burn patterns (plus, it's just plain fun to turn the flame different colors).

You can find most of the densities for plastics online. Some common density solutions are: saturated NaCl, 10% NaCl, plain water, 46% isopropyl alcohol, and vegetable oil.

Thank you so much for the other solutions for density! I couldn't figure out what they were. Now I can test them.
And the other info was helpful as well. Thank you!

[claribassist13]

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?

[Phenylethylamine]

As knittingfrenzy18 said, glucose but not sucrose will react with Benedict's - it will turn orange-ish when heated and left to sit for a little while. However ammonium chloride will also react to form a blue-purple color with Benedict's and KCl may or may not turn green when heated (there was a discussion on this a few pages back; you should probably read through that since I can't recall exactly what we established reaction-wise for KCl and its cousin LiCl).

When I tested this, LiCl + Benedict's + heat gave a visible lime-green color in the bottom of the test tube, but KCl gave nothing (even though it should ostensibly undergo the same reaction; I guess it's just not favorable enough to see much of the product).

[meggers1221]

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....

[Steelfoam]

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....

I think MgSO4 is soluble xD. but the question is does Ca(NO3)2 precip? wikipedia says thats the would be precip CaOH2 is slightly soluble? has anyone tried NaOH + Ca(NO3)2?