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Re: Crime Busters B

Posted: December 2nd, 2017, 2:32 pm
by ashleybrown5
How do you separate two powders that are mixed together? ex. baking soda and calcium carbonate

Re: Crime Busters B

Posted: December 2nd, 2017, 3:12 pm
by shrewdPanther46
ashleybrown5 wrote:How do you separate two powders that are mixed together? ex. baking soda and calcium carbonate

A good explanation for this is in the wiki. Generally, I just look for distinguishable properties from multiple powders.

I have a question pertaining to the analysis "questions" that are generally asked at the end. Is it necessary to write in full sentences, or can a list be presented? Most test have an open ended question and a bunch of lines underneath (like nationals). Could someone please let me know if a list could be used (mainly at higher level competitions) ? I am aware that this could vary between supervisors, but I would like to know the general consensus.

Thanks!

Re: Crime Busters B

Posted: January 1st, 2018, 6:18 am
by SOCoach
Several years ago I bought a polymer / fiber kit for crimebusters that was really good. I can't seem to remember or find where I bought it from. Does anyone have a good site for getting fibers and plastics for crimebusters?

Re: Crime Busters B

Posted: January 2nd, 2018, 6:17 pm
by knowthewrightstuff
My team has had trouble identifying the difference between water and hydrogen peroxide since they are both odorless and have the same pH. We have tried shaking them and looking for bubbles, but both liquids bubble for us. Are there other methods we could try to effectively identify the difference between these liquids?

Re: Crime Busters B

Posted: January 2nd, 2018, 7:27 pm
by shrewdPanther46
knowthewrightstuff wrote:My team has had trouble identifying the difference between water and hydrogen peroxide since they are both odorless and have the same pH. We have tried shaking them and looking for bubbles, but both liquids bubble for us. Are there other methods we could try to effectively identify the difference between these liquids?

You probs have some old, old peroxide. Spontaneous decomposition

Re: Crime Busters B

Posted: January 2nd, 2018, 11:46 pm
by knowthewrightstuff
shrewdPanther46 wrote:
knowthewrightstuff wrote:My team has had trouble identifying the difference between water and hydrogen peroxide since they are both odorless and have the same pH. We have tried shaking them and looking for bubbles, but both liquids bubble for us. Are there other methods we could try to effectively identify the difference between these liquids?

You probs have some old, old peroxide. Spontaneous decomposition

Thanks for the advice. We did notice that our bottle was expired last year so we bought a new bottle, but we still had the same problem. Do you just use a plastic test tube to shake it in?

Re: Crime Busters B

Posted: January 3rd, 2018, 4:45 am
by shrewdPanther46
We have glass, but its more or less the same.

Re: Crime Busters B

Posted: January 3rd, 2018, 9:05 am
by Tailsfan101
knowthewrightstuff wrote:My team has had trouble identifying the difference between water and hydrogen peroxide since they are both odorless and have the same pH. We have tried shaking them and looking for bubbles, but both liquids bubble for us. Are there other methods we could try to effectively identify the difference between these liquids?

One way to tell them apart is to put some iodine in it. If it fizzes, it's hydrogen peroxide. If not, water.

Re: Crime Busters B

Posted: January 3rd, 2018, 10:53 am
by pikachu4919
SOCoach wrote:Several years ago I bought a polymer / fiber kit for crimebusters that was really good. I can't seem to remember or find where I bought it from. Does anyone have a good site for getting fibers and plastics for crimebusters?


The Society of Plastics Engineers sells a pretty comprehensive kit called Hands-On Plastics that has most everything except PMMA. A cheap way to get fibers is to go to the local craft/fabric store and see if they'll let you have 1-inch samples of fabrics for free or for really cheap.

Tailsfan101 wrote:
knowthewrightstuff wrote:My team has had trouble identifying the difference between water and hydrogen peroxide since they are both odorless and have the same pH. We have tried shaking them and looking for bubbles, but both liquids bubble for us. Are there other methods we could try to effectively identify the difference between these liquids?

One way to tell them apart is to put some iodine in it. If it fizzes, it's hydrogen peroxide. If not, water.


I'm not sure how you got that to happen bc if you try to write a balanced equation for it, you won't get a product that will be in gaseous form.

Re: Crime Busters B

Posted: January 3rd, 2018, 11:52 am
by Unome
pikachu4919 wrote:
Tailsfan101 wrote:
knowthewrightstuff wrote:My team has had trouble identifying the difference between water and hydrogen peroxide since they are both odorless and have the same pH. We have tried shaking them and looking for bubbles, but both liquids bubble for us. Are there other methods we could try to effectively identify the difference between these liquids?

One way to tell them apart is to put some iodine in it. If it fizzes, it's hydrogen peroxide. If not, water.


I'm not sure how you got that to happen bc if you try to write a balanced equation for it, you won't get a product that will be in gaseous form.

I found something on the H2O2/KI reaction here.

Re: Crime Busters B

Posted: January 3rd, 2018, 12:02 pm
by pikachu4919
Unome wrote:
pikachu4919 wrote:
Tailsfan101 wrote:One way to tell them apart is to put some iodine in it. If it fizzes, it's hydrogen peroxide. If not, water.


I'm not sure how you got that to happen bc if you try to write a balanced equation for it, you won't get a product that will be in gaseous form.

I found something on the H2O2/KI reaction here.


OK, I stand corrected... even so, I'm not entirely sure the gas released is always guaranteed to produce an audible fizzing sound like HCl + carbonate does? Even elephant toothpaste isn't that loud although it's a lot more pretty to watch XD

Re: Crime Busters B

Posted: January 5th, 2018, 7:05 am
by Tailsfan101
Does anyone know any easy ways to tell the difference between LDPE and HDPE? Those are the only plastics I've really been struggling with.

Re: Crime Busters B

Posted: January 8th, 2018, 8:07 pm
by pikachu4919
Tailsfan101 wrote:Does anyone know any easy ways to tell the difference between LDPE and HDPE? Those are the only plastics I've really been struggling with.


Your best bet is density, and that's at the mercy of your event supervisor to hopefully make something that's around 0.93-0.94 g/cm^3 since that's in the middle of the densities of HDPE and LDPE.

Re: Crime Busters B

Posted: January 10th, 2018, 7:00 am
by Tailsfan101
pikachu4919 wrote:
Tailsfan101 wrote:Does anyone know any easy ways to tell the difference between LDPE and HDPE? Those are the only plastics I've really been struggling with.


Your best bet is density, and that's at the mercy of your event supervisor to hopefully make something that's around 0.93-0.94 g/cm^3 since that's in the middle of the densities of HDPE and LDPE.

Thanks!

Re: Crime Busters B

Posted: January 12th, 2018, 3:47 pm
by pandascienceolympiad
You have to also make sure that both of the substances are new and are not old. If they are old, they might not work