Crime Busters B

[pikachu4919]

2022 Question Marathon Thread for Crime Busters B.

Question Marathons Explained

[aakoala]

Let's get this marathon started!

1. Anna is observing a hair under a microscope, but (for some unknown reason) can't determine whether it is cat hair or dog hair. Other than using the medulla, what are two other ways to differentiate between cat and dog hair?

2. Albert is performing paper chromatography on a marker and notices that the compound spot is 2 centimeters behind the solvent front. If the solvent front is 8 centimeters away from the baseline, determine the Rf, and decide whether the marker is hydrophilic or hydrophobic.

3. Avery burned a plastic grocery bag. If Avery only observed the color of the flame, what plastics might he identify it as?

[MahathiR]

1) the cuticle types are different, cat is spinous and dog is coronal.
2)0.25, hyrdophobic?
3)if it was green, pvc? sry this question sin't clear

[aakoala]

For #2, since the solvent front is 8 cm above the baseline, and the compund spot is 2 cm behind the solvent front, the compound spot is 6 cm above the baseline. This means that the rf is 6/8, or 0.75.
For #3, I apologize for making it unclear. But yes, if there were green spurts, it would be PVC.

Your turn!

[MahathiR]

Which powders can't have a definite chemical formula?

Which two powders can you guess given pH?

Why do liquids, hydrogen peroxide specifically, need to be stored in dark containers?

[aakoala]

Which powders can't have a definite chemical formula?

Which two powders can you guess given pH?

Why do liquids, hydrogen peroxide specifically, need to be stored in dark containers?

1. Not exactly sure, but yeast, flour, cornstarch, and gelatin since they come from organic sources?
2. Vitamin C and ???
3. Hydrogen peroxide needs to be stored in dark containers because sunlight can break hydrogen peroxide into water and oxygen gas, which is no longer hydrogen peroxide.

My new questions:
1. If a blood sample agglutinates in Antigen-A, and Antigen-B, but not Antigen-D, what are all the blood types that can donate to this person?
2. Briefly describe the pH scale, including the reason it spans from 1 to about 14.
3. What type of soil is 36% silt, 54% sand, and 10% clay?

[MahathiR]

1 - not cornstarch, but everything else is correct,
2- sodium acetate too, but u could argue baking soda has a similar pH
3 - correct, gj!
for ur questions -
1 - a, b, ab, o
2 - the pH scale is a logarithmic scale that measures the hydrogen ion concentration, the reason its 1-14 is because the hydrogen ion concentration per mole can't be lower or higher?
3) loam or sandy loam - im not sure

[aakoala]

1. Since the blood agglutinates in Antigen-A and B but not D, this is type AB- blood. The answers I was looking for were A-,B-, O-, and AB-. Someone with a positive blood type would not be able to donate to this person.
2. Correct! It's also very important to note that the lower end of the scale is a higher concentration than the higher end, and that this concentration is a measure of hydrogen ions (H+).
3. It's really on the borderline, so I would accept either answer.

Your turn!

[MahathiR]

1) Describe and include the temperatures of the PCR stages
2)A solution of water and powder x is conductive and has a pH of 7, identify the powder x.
3)Given a fingerprint on a porous surface, what would be the best method to view it?

[aakoala]

Sorry for the really late answer!

Click to Show Answer

1. Denaturing heats the DNA strands to a very high temperature to break the double helix of DNA. Around 95 C. Annealing: Primers bind to the DNA strands. Around 55 C. Extending/Synthesis: Complementary strands of DNA are built. Around 72 C
2. Salt
3. Ninhydrin (could also be iodine fuming)

1. Explain why identical twins don't have the same fingerprints.
2. What type of scales do humans have on their hair?
3. Johanna is trying to determine a powder. The powder turns black in iodine. What additional test does she need to perform to figure out its identity? Why?
4. Which of the following has the smallest particle size?
A) Sand
B) Silt
C) Clay