Forensics C

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Panda Weasley
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Re: Forensics C

Postby Panda Weasley » December 29th, 2016, 8:57 am

I never quite understood how to do density tests- Do you use a beaker and fill the whole thing up with liquid? Or can you use test tubes? Plastics have always been a part of the test I just guessed on.
If you're doing plastics, the event supervisor will provide solutions of different densities. Since you can bring a chart with the densities of each plastic and the densities of the solutions, you can tell which plastics will sink/float in which solutions. At the event, you take the plastic and simply place it in the liquid to see whether it floats or sinks.
So for example, if the supervisors provide us with a large bottle of alcohol for a row to share, we can just dunk the plastic directly into the alcohol container?
The solutions are typically in large beakers that you share with everyone (from my experience). Make sure you remember to take your plastics out. Don't be that person!
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Re: Forensics C

Postby bradyr18 » January 3rd, 2017, 4:47 pm

Has anyone found a reliable conductivity tester? We've tried both homemade testers and flinn science testers and neither has consistently worked for us? Thanks

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Re: Forensics C

Postby pikachu4919 » January 4th, 2017, 11:07 am

Has anyone found a reliable conductivity tester? We've tried both homemade testers and flinn science testers and neither has consistently worked for us? Thanks
Is your issue that the tester always lights up with a dissolved solution of any powder?
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Re: Forensics C

Postby bradyr18 » January 4th, 2017, 11:25 am

Has anyone found a reliable conductivity tester? We've tried both homemade testers and flinn science testers and neither has consistently worked for us? Thanks
Is your issue that the tester always lights up with a dissolved solution of any powder?
One of the testers (our homemade one) always lit up on solution, the other (Flinn) never lit up which may have been from a bad lightbulb

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Re: Forensics C

Postby pikachu4919 » January 4th, 2017, 12:54 pm

Has anyone found a reliable conductivity tester? We've tried both homemade testers and flinn science testers and neither has consistently worked for us? Thanks
Is your issue that the tester always lights up with a dissolved solution of any powder?
One of the testers (our homemade one) always lit up on solution, the other (Flinn) never lit up which may have been from a bad lightbulb
I remember a couple years ago we ran into the same problem with our testers always lighting up, and we figured out the reason why the homemade one always lights up is because of strong vs weak electrolytes. Some of the powders will completely dissolve in water, and the presence of so many dissociated particles allow the solution to very effectively conduct electricity, which will cause the bulbs on the tester to shine very brightly. But there are other powders that are weak electrolytes, which will dissolve in water, but not completely dissociate like strong electrolytes. Those ones will still be able to conduct electricity, but not as well, so the bulbs will still shine, but the light given off will be significantly weaker. A good way to test this is to look at NaCl (a strong electrolyte) vs. sucrose (a weak one).

There are three possibilities for the Flinn one: 1. It's not on (it has an on/off switch), 2. the 9V battery is dead, 3. as you said, the lightbulb is dead. Check those before buying a new one.
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Re: Forensics C

Postby 18alia » January 8th, 2017, 3:33 pm

Hi guys, does anyone have the results for reacting powders with NaOH? It's not on the wiki, and we don't have the resources to run the tests ourselves.

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Re: Forensics C

Postby Lumitailz » January 8th, 2017, 8:04 pm

Hi guys, does anyone have the results for reacting powders with NaOH? It's not on the wiki, and we don't have the resources to run the tests ourselves.
I'm pretty sure it precipitates with all the calcium and magnesium salts, and reacts with ammonium salts to form NH3

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Re: Forensics C

Postby sciduck » January 15th, 2017, 8:15 am

What is the percentage distribution for fingerprints? Some test keys say 70% loops, 25% whorls, and 5% arches while others say 65% loops, 30% whorls, and 5% arches.
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Re: Forensics C

Postby Magikarpmaster629 » January 15th, 2017, 9:47 am

What is the percentage distribution for fingerprints? Some test keys say 70% loops, 25% whorls, and 5% arches while others say 65% loops, 30% whorls, and 5% arches.
I see the first one more often I think
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Re: Forensics C

Postby 18alia » January 23rd, 2017, 11:42 am

Does anyone have the density values for different NaCl solutions? The only one I could find was 10%, and according to the wiki, 25% and saturated are often available for density tests.


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