Crime Busters B

[sciolylover13]

Does anyone know how to differentiate hydrogen peroxide and water? My coach said hydrogen peroxide should smell weird, but I can't tell the difference.

[Panda Weasley]

Does anyone know how to differentiate hydrogen peroxide and water? My coach said hydrogen peroxide should smell weird, but I can't tell the difference.

Hydrogen peroxide will react with other certain substances (can't look any up right now but I know that there is one with baking soda). You can also sometimes see bubbles.

[samlan16]

Does anyone know how to differentiate hydrogen peroxide and water? My coach said hydrogen peroxide should smell weird, but I can't tell the difference.

The iodine test. KI should react slowly with the peroxide to form some gas, which means it will form bubbles after a while. Obviously, it will do nothing with water.

[sciolylover13]

Does anyone know how to differentiate hydrogen peroxide and water? My coach said hydrogen peroxide should smell weird, but I can't tell the difference.

The iodine test. KI should react slowly with the peroxide to form some gas, which means it will form bubbles after a while. Obviously, it will do nothing with water.

Ok thanks!

[whovian11]

I'm not sure but I think that when you shake hydrogen peroxide there will be bubbles. you can always tell for a few things on just smell.

[ampy1234567]

How do you test the pH of powders? (especially cornstarch, as it's insoluble and if you can't find the pH it's really hard to differentiate from flour)
Also, how are you supposed to ID mixtures? Do you try to separate each powder or do you test them together?

[sciolylover13]

How do you test the pH of powders? (especially cornstarch, as it's insoluble and if you can't find the pH it's really hard to differentiate from flour)
Also, how are you supposed to ID mixtures? Do you try to separate each powder or do you test them together?

For cornstarch and flour, you should be able to tell the difference by looking and feeling (if you know that the unknown is either cornstarch or flour). Cornstarch should be pure white, and flour should be off-white. Also, cornstarch will feel slippery, and flour will not.

You test mixtures together. For mixtures, the mixture should have 2 identifying properties. For example, for cornstarch and alka-seltzer, the cornstarch will cause the iodine to turn a blackish blue color, and the alka-seltzer will fizz in HCl and H2O.

[christseeker]

Hi, I am coaching my kids at home for the first time for CB event. I have a question for testing polymers. I will first describe what we did today and then ask my questions.

I provided them water, 70% alcohol, and saturated salt solution for testing solutions. And I gave them all 6 polymers to test (don't have PMMA yet). So the 3 that floated were LDPE, HDPE, PP, and the 3 that sunk were PVC, PS, PETE. This was the simple part. Next they used the 70% alcohol to test the 3 that floated, and they all sunk in alcohol. Then adding a little water at a time, PP started floating first, then LDPE, and HDPE remained sunk. For the other 3 that sunk in water, they next used saturated salt solution, and PS floated, but PETE and PVC remained sunk.

Questions:
1) How do I go about distinguishing PETE and PVC from here?
2) One flow chart used Calcium Chloride. Is it necessary? Do I have other options?
3) Is this approach to testing polymers adequate? In the competition, not all polymers will be given right? If that is the case, then there will really be no way to compare which polymers float first or second or last, then how would they know how to identify the specific polymer?
4) What testing solutions are generally provided for testing?
5) Will the density of these solutions be given? If so, then simply by comparing the density of solutions to the density of polymers will suffice right? This makes it seems really easy!

Sample tests are not very helpful in figuring out the answers to these questions.

[whovian11]

for the ph, I put in the powder then water then the ph paper I always get the right results. also for good studying go to quizlet and take the test.

[christseeker]

I got the following info from the internet, is this true? My pellets sure don't match what is described.

"What do these pellets feel like?
P.E. pellets feel like half of a sphere, and P.V.C. pellets are smaller than P.E. pellets, they feel cylinder but round on one side."