Forensics C

[samlan16]

What am I looking for in NaOH tests? There doesn't seem to be much going on...

Try reacting MgSO4 with NaOH- a precipitate of Na2SO4 should result.

You mean a Mg(OH)2 precip, right? Oh, adding onto that, Ca(NO)3 can also precip to form Ca(OH)2, which is also known as lime (not the fruit - if you've ever heard of limewater, that's a component of it), but the Mg(OH)2 is generally a lot more gel-looking and solid than the Ca(OH)2, which is more powdery although it still forms a settling solid. This is because Mg(OH)2 is completely insoluble while Ca(OH)2 is marginally soluble.

Oh yeah, fail. I was thinking BaSO4 and not Na2SO4.

[QuantumTech]

Regarding index of refraction for glass, what is the method to identify the type of glass at a crime scene? Is it simply to place pieces of the glass in different liquids and see if it is clear, then use the index of refraction of the liquid to match it to the type of glass?

[pikachu4919]

Regarding index of refraction for glass, what is the method to identify the type of glass at a crime scene? Is it simply to place pieces of the glass in different liquids and see if it is clear, then use the index of refraction of the liquid to match it to the type of glass?

Yep, that's basically it.

[4n6nerd]

Does anyone know how to tell PC and PMMA apart?

[Magikarpmaster629]

On previous years' threads people have said the nationals test is ridiculously long; over 200 questions. How...how do you even get through half of it? Our state test was around 35 questions plus a write-up, and we barely had time to finish. Although from the previous threads it sounds like each individual question is easier, like some basic chemical reaction and identifying evidence with certain suspects.

[Unome]

On previous years' threads people have said the nationals test is ridiculously long; over 200 questions. How...how do you even get through half of it? Our state test was around 35 questions plus a write-up, and we barely had time to finish. Although from the previous threads it sounds like each individual question is easier, like some basic chemical reaction and identifying evidence with certain suspects.

You don't get through half of it; you get through 70% of it (if you're exceptionally good) and if you managed your time well, you have a shot at a medal (at least this is my understanding of it).

[daydreamer0023]

Does anyone know if they provide microscopic images at nationals of the different fibers at the crime scene to help with identification? Or do you have to tell by feel/burn tests (if this is the case, then what are some distinct physical charecteristics if we can't use microscope pictures)?

Also, what is the difference, in pictures, between human, mammal, avian, and reptile blood? I don't quite get that. A simple explanation of mass spec would help too - I've looked online and found some nice websites, but most of it goes over my head.

[sciduck]

Does anyone know if they provide microscopic images at nationals of the different fibers at the crime scene to help with identification? Or do you have to tell by feel/burn tests (if this is the case, then what are some distinct physical characteristics if we can't use microscope pictures)?

Also, what is the difference, in pictures, between human, mammal, avian, and reptile blood? I don't quite get that. A simple explanation of mass spec would help too - I've looked online and found some nice websites, but most of it goes over my head.

I have never been to Nationals, but one website says:
-know how to do a burn test on only one strand of fiber
-don’t use more than one strand, which is more difficult than a ball
-be prepared to make an identification using a microscope making your own wet mount (this will NOT already be done for you)
Source: http://www.raleighcharterhs.org/student ... ensics.asp

As for blood:
-Mammalian blood cells don't have nuclei and organelles for two reasons. The first is an adaption to increase oxygen carrying potential by making more room for hemoglobin. The second is increased flexibility to pass through small capillaries.
-Human blood cells are spherical.
-Avian blood cells are very elliptical and have nuclei. Imagine pink rice with nuclei.
-Fish blood cells have nuclei and are bigger than human blood cells, but smaller than frog blood cells. They also have less types of lymphocytes than humans.
-I don't know how to tell the difference between human blood and other mammals (with the exception of camels) and I also can't tell the difference between reptiles and amphibians (amphibian blood cells maybe rounder? Might just be my specific set of pictures, I don't really know). I just printed out some pictures and hoped it wouldn't show up, but let me know if you find out how.

Good luck at Nationals!

[justgreene]

How does TLC work at nationals? Are we supposed to conduct it ourselves like we would for paper chromatography? Also can somebody explain the short vs. long wavelength UV radiation stuff for TLC fluorescence that I've seen on past nationals tests.

[pikachu4919]

On previous years' threads people have said the nationals test is ridiculously long; over 200 questions. How...how do you even get through half of it? Our state test was around 35 questions plus a write-up, and we barely had time to finish. Although from the previous threads it sounds like each individual question is easier, like some basic chemical reaction and identifying evidence with certain suspects.

You don't get through half of it; you get through 70% of it (if you're exceptionally good) and if you managed your time well, you have a shot at a medal (at least this is my understanding of it).

Lol this seems a bit late since Nats has passed already, but splitting the work with your partner always works. But lol Unome is essentially correct on what he/she said.

Does anyone know if they provide microscopic images at nationals of the different fibers at the crime scene to help with identification? Or do you have to tell by feel/burn tests (if this is the case, then what are some distinct physical characteristics if we can't use microscope pictures)?

Also, what is the difference, in pictures, between human, mammal, avian, and reptile blood? I don't quite get that. A simple explanation of mass spec would help too - I've looked online and found some nice websites, but most of it goes over my head.

I have never been to Nationals, but one website says:
-know how to do a burn test on only one strand of fiber
-don’t use more than one strand, which is more difficult than a ball
-be prepared to make an identification using a microscope making your own wet mount (this will NOT already be done for you)
Source: http://www.raleighcharterhs.org/student ... ensics.asp

As for blood:
-Mammalian blood cells don't have nuclei and organelles for two reasons. The first is an adaption to increase oxygen carrying potential by making more room for hemoglobin. The second is increased flexibility to pass through small capillaries.
-Human blood cells are spherical.
-Avian blood cells are very elliptical and have nuclei. Imagine pink rice with nuclei.
-Fish blood cells have nuclei and are bigger than human blood cells, but smaller than frog blood cells. They also have less types of lymphocytes than humans.
-I don't know how to tell the difference between human blood and other mammals (with the exception of camels) and I also can't tell the difference between reptiles and amphibians (amphibian blood cells maybe rounder? Might just be my specific set of pictures, I don't really know). I just printed out some pictures and hoped it wouldn't show up, but let me know if you find out how.

Good luck at Nationals!

Although the rules say to know it, Woz generally doesn't use microscope images for hair. I think she used to, but she hasn't on all the tests I've seen recently. She does use them for blood if she includes animal blood as part of the crime scenario.

How does TLC work at nationals? Are we supposed to conduct it ourselves like we would for paper chromatography? Also can somebody explain the short vs. long wavelength UV radiation stuff for TLC fluorescence that I've seen on past nationals tests.

Lol also a bit late for this one, but yeah you do it yourself. Woz always makes you do it yourself. And the short vs long wavelength is a setting on the blacklight, and I think you just see if it glows. Tbh at nats I actually skipped most of the TLC questions bc honestly if you get enough ID's and trivia questions right, it'll make up for it anyways.