Forensics C

[salcedam]

Thanks! Also, how do you tell the difference between the sodium compounds (NaCl, NaC2H3O2, etc.) and the calcium compounds (CaCO3, CaSO4)? Whenever I perform the flame tests, both flames look orange to me...

Apparently calcium nitrate sparks in addition to its orange flame (although, disclaimer, I can't say I've ever observed this myself), and calcium carbonate and calcium sulfate are both insoluble, which separates them from all the sodium compounds.

Calcium nitrate does burn with a strikingly darker orange than the more yellow-ish color of sodium compounds. And in terms of burn tests for calcium carbonate and calcium sulfate, you can also observe how they burn (or rather, how they don't burn). When you burn sodium compounds, you can see how they actually burn away. Calcium sulfate and calcium carbonate do not burn away. You should notice how if you burn calcium sulfate, it just stays the same as it was before (just hotter). And calcium carbonate glows, but it doesn't burn away. But besides the burn tests, as Phenylethylamine said, calcium carbonate and calcium sulfate are both insoluble as opposed to the sodium compounds and calcium nitrate.

[TheWiseGirl]

On my regional test we were given chromatography results and asked to find the Rf value. However, it only asked for 1 Rf value (or seemed to, since there was one short line for our answer). However, there were 3 distinct ink particles. So in this case do I just find all 3 anyways and label them, or is there one specific pigment I should find the Rf value of? Thanks!

[salcedam]

On my regional test we were given chromatography results and asked to find the Rf value. However, it only asked for 1 Rf value (or seemed to, since there was one short line for our answer). However, there were 3 distinct ink particles. So in this case do I just find all 3 anyways and label them, or is there one specific pigment I should find the Rf value of? Thanks!

In that sort of situation, I would go ask the proctor if they're looking for one specific Rf value or all three. If the proctor doesn't know what you're talking about, the safe bet would be to go for whichever particle traveled the farthest because that's probably the Rf the proctor used rather than the other particles. Otherwise, give all three just in case and label them.

[Steelfoam]

Does anyone have a good link for entomology? How in-depth of a question would the ask about it. I don't have any specific hours of each insect.

[TheWiseGirl]

On my regional test we were given chromatography results and asked to find the Rf value. However, it only asked for 1 Rf value (or seemed to, since there was one short line for our answer). However, there were 3 distinct ink particles. So in this case do I just find all 3 anyways and label them, or is there one specific pigment I should find the Rf value of? Thanks!

In that sort of situation, I would go ask the proctor if they're looking for one specific Rf value or all three. If the proctor doesn't know what you're talking about, the safe bet would be to go for whichever particle traveled the farthest because that's probably the Rf the proctor used rather than the other particles. Otherwise, give all three just in case and label them.

Thank you!!!!

[bloods]

Does anyone have a good link for entomology? How in-depth of a question would the ask about it. I don't have any specific hours of each insect.

In my two years I haven't seen anything entomology-related, but I make sure to know the stages of a blowfly and which beetles arrive first.

[Dragonshark]

I'm almost finished with my flowchart for qualitative analysis. On average, how long should it take you to identify 8 powders? I'm going to time myself with this soon, but I'd like to know what a 'good' time would be beforehand.

Uh, could anyone answer this question? If it feels like I'm asking too many questions, I apologize, but State is in less than a week, and I'm desperately cramming.

[Phenylethylamine]

I'm almost finished with my flowchart for qualitative analysis. On average, how long should it take you to identify 8 powders? I'm going to time myself with this soon, but I'd like to know what a 'good' time would be beforehand.

Uh, could anyone answer this question? If it feels like I'm asking too many questions, I apologize, but State is in less than a week, and I'm desperately cramming.

No such thing as too many questions – this one's just a little hard to answer. I know that, ideally, I'd like to spend between half and three-quarters of the full time (40 min, not counting cleanup) on powders, and the number of powders to identify can vary significantly. I guess 8 is a fairly low number of powders to have on an event... so I'd say probably 20 minutes.

[JustDroobles]

I'm almost finished with my flowchart for qualitative analysis. On average, how long should it take you to identify 8 powders? I'm going to time myself with this soon, but I'd like to know what a 'good' time would be beforehand.

No such thing as too many questions – this one's just a little hard to answer. I know that, ideally, I'd like to spend between half and three-quarters of the full time (40 min, not counting cleanup) on powders, and the number of powders to identify can vary significantly. I guess 8 is a fairly low number of powders to have on an event... so I'd say probably 20 minutes.

It depends how you split the work between the partners. Usually my partner spends about 35 minutes doing powders while I do the polymers, chromatography, and physical evidence. Then we finish up any odds and ends, and write our analysis.

[Phenylethylamine]

I'm almost finished with my flowchart for qualitative analysis. On average, how long should it take you to identify 8 powders? I'm going to time myself with this soon, but I'd like to know what a 'good' time would be beforehand.

No such thing as too many questions – this one's just a little hard to answer. I know that, ideally, I'd like to spend between half and three-quarters of the full time (40 min, not counting cleanup) on powders, and the number of powders to identify can vary significantly. I guess 8 is a fairly low number of powders to have on an event... so I'd say probably 20 minutes.

It depends how you split the work between the partners. Usually my partner spends about 35 minutes doing powders while I do the polymers, chromatography, and physical evidence. Then we finish up any odds and ends, and write our analysis.

Yes, that's more or less how we split it up, as well – but a large fraction of the points (and typically most of the tiebreakers, when there are specific ones) are in the analysis, so it helps to have a significant chunk of time left to figure out what actually makes sense to write.