Forensics C

[Steelfoam]

Does anyone have a good way of telling Ca(NO3)2 from MgSO4 without the use of the flame test?

[Kokonilly]

For example, at one time I was using a flow chart essentially unmodified off the Internet, and one difference relied on the smell produced by adding a reagent to a particular powder. I have a terrible sense of smell, and often couldn't tell whether the mixture smelled like anything, which made that method less than ideal for me. I've since learned to identify the odor, but it did take practice.

Out of curiosity, which powder was this? The only powder I used an odor to identify was ammonium chloride (added to NaOH), and that wasn't so much an odor as it was a scalding of the nasal passages.

[BoldlyGoingNowhere]

For paper chromatography, do you calculate the Rf values using the middle of the pigment smudge/blob or do you calculate it using the top of the pigment line? I looked online and I know both are used. For Tiger, I used the top of the pigment and lost points for being not exact since the event supervisor made the answer key using the middle. Is there any preference to the top or the middle?

The proper way to measure paper chromatography is from the original mark of the compound to the middle of the component. This is divided by the distance from the mark to the solvent front (where the solvent stops moving).

[Phenylethylamine]

For example, at one time I was using a flow chart essentially unmodified off the Internet, and one difference relied on the smell produced by adding a reagent to a particular powder. I have a terrible sense of smell, and often couldn't tell whether the mixture smelled like anything, which made that method less than ideal for me. I've since learned to identify the odor, but it did take practice.

Out of curiosity, which powder was this? The only powder I used an odor to identify was ammonium chloride (added to NaOH), and that wasn't so much an odor as it was a scalding of the nasal passages.

Yes, it was ammonium chloride, and my sense of smell is so bad (i.e., I have so much trouble distinguishing between odors, particularly strong ones) that among all the other random smells of a Forensics event room, I couldn't tell that it smelled like ammonia (when mixed with NaOH).

This was even more of a problem in B division Science Crime Busters, because we had to identify liquids, some of which were mainly identifiable based on smell... I always had to have my partner smell them, as I couldn't tell the difference between ammonia and vinegar.

[salcedam]

For example, at one time I was using a flow chart essentially unmodified off the Internet, and one difference relied on the smell produced by adding a reagent to a particular powder. I have a terrible sense of smell, and often couldn't tell whether the mixture smelled like anything, which made that method less than ideal for me. I've since learned to identify the odor, but it did take practice.

Out of curiosity, which powder was this? The only powder I used an odor to identify was ammonium chloride (added to NaOH), and that wasn't so much an odor as it was a scalding of the nasal passages.

If you have trouble telling ammonium chloride by smell, you could always use Benedict's to double-check to make sure it really is ammonium chloride.

[Phenylethylamine]

For example, at one time I was using a flow chart essentially unmodified off the Internet, and one difference relied on the smell produced by adding a reagent to a particular powder. I have a terrible sense of smell, and often couldn't tell whether the mixture smelled like anything, which made that method less than ideal for me. I've since learned to identify the odor, but it did take practice.

Out of curiosity, which powder was this? The only powder I used an odor to identify was ammonium chloride (added to NaOH), and that wasn't so much an odor as it was a scalding of the nasal passages.

If you have trouble telling ammonium chloride by smell, you could always use Benedict's to double-check to make sure it really is ammonium chloride.

Yeah, there are other ways of identifying it, which was kind of my point: make sure that your flow chart only includes tests that actually allow you personally to tell the difference, especially since there are often many ways of going about it.

[Dragonshark]

Does anyone know how to tell sodium chloride and sodium acetate apart?

[Phenylethylamine]

Does anyone know how to tell sodium chloride and sodium acetate apart?

Sodium acetate dissolved in water makes a basic solution; sodium chloride dissolved in water makes a neutral solution.

[Dragonshark]

Does anyone know how to tell sodium chloride and sodium acetate apart?

Sodium acetate dissolved in water makes a basic solution; sodium chloride dissolved in water makes a neutral solution.

OK, thanks. Also, is it a good idea to base observations on a powder based on its general appearance? For example, calcium sulfate, calcium carbonate, and cornstarch have similar appearances (lumpy, white powder) but the other powders don't. They also happen to be nonsoluble, and from experience, I'm not that good at telling whether a powder is soluble, so could appearance replace the solubility test for them?
Also, how can one distinguish magnesium sulfate, if it has any distinguishing properties? (from the magnesium sulfate I've seen, the individual grains are very large and irregular, but I doubt this is a consistent property in all possible samples of magnesium sulfate.)

[haverstall]

Does anyone know how to tell sodium chloride and sodium acetate apart?

Sodium acetate dissolved in water makes a basic solution; sodium chloride dissolved in water makes a neutral solution.

OK, thanks. Also, is it a good idea to base observations on a powder based on its general appearance? For example, calcium sulfate, calcium carbonate, and cornstarch have similar appearances (lumpy, white powder) but the other powders don't. They also happen to be nonsoluble, and from experience, I'm not that good at telling whether a powder is soluble, so could appearance replace the solubility test for them?

I've always wanted to ID powders like that, but I wouldn't bank on it. It's possible to change the appearance (crush the powders for example), and therefore, you could get thrown off. Just wondering, but how are you having trouble with the solubility tests?