Need help urgent!

[Catalyst]

I need to make an experiment that proves either Boyle's, Charles, or Gay Lussac's law by tomorrow morning. The simpler the better please as I don't have the time to get any advanced material. Any helped would be extremely appreciated!

[budullewraagh]

do you need to actually perform the experiment or do you need to explain it?

[Catalyst]

I need to actually make it in front of my class.

[H2SO4]

for charles law you can put alittle water in a soda can, bring it to a slight boil, then with tongs quickly upturn it and put it facing down in a bucket of water. The gassses inside will rapidy cool and cause the can to crush instantly as soon as it hits the water. Very dramatic demo.

[Catalyst]

hey that sounds awesome would you mind explaining it a little more detailed? I also have to give an explanation of why it is happening and make a whole science report on it so info is appreciated

[jdurg]

This works even better if you use one of those metal paint thinner containers that you see at hardware stores. (Just make sure you use an empty container. A metal container with a screw on cap works best for this experiment). What you do is take the empty container and put a small bit of water in there. Take the metal container and put it on a hot plate so that you can get the water to boil and form steam. While the water is heating up, you get a big container and fill it with water and ice.

 

Once you see steam coming out of the heating metal container, you quickly screw the cap on to lock the hot water vapor in there. Inside the metal container, you have water in there as a gas at a high temperature. At the elevated temperature, the gas in there fills up the entire volume of the container. If you then take the container and dunk it into the ice-water filled bath, the temperature of the gas inside the container immediately drops. As a result, the volume of that gas drops as well which lowers the pressure inside the container. The external atmospheric pressure is MUCH greater than the low pressure that now exists inside the container, and the container will be crushed almost instantly because of that. At higher temperature, the same amount of gas has a higher pressure than it does at a lower temperature. This experiment shows that fact.

[Catalyst]

I love you man you just saved me from failing chemistry =D

[Catalyst]

oh by the way, I will be using normal soda cans will that be fine? Because you said something about screwing a cap and cans dont have caps.

[akcapr]

ya that will work fine. quick procedure over view: heat the cans opening in a bunsen burner while holding with tongs, then, dip it into a bowl of ice cold water opening first. Observe the can totally collapse.

[Bettina]

for charles law you can put alittle water in a soda can, bring it to a slight boil, then with tongs quickly upturn it and put it facing down in a bucket of water. The gassses inside will rapidy cool and cause the can to crush instantly as soon as it hits the water. Very dramatic demo.

 

That sounds cool...I'm going to try this tommorrow in school......

 

Bettina

[jdurg]

Yeah, an open soda can will work, but you have to move a bit faster to prevent the hot air from leaving the can. Also, inverting the can when you dunk it is a great idea as hot air rises so having the opening on the bottom will keep the hot air in there. When I've done this in the past I've used a screw top container mostly because they were readily available. Plus, this allowed me to put the can in an empty container and just pour ice water over it and watch the can suddenly get crushed by the atmosphere.

[jdurg]

I've also seen the experiment done with 55 gallon steel drums that were filled with hot steam and then sealed off. Bags of ice were then thrown on the drums, and almost instantly they imploded due to atmospheric pressure. It was amazing to see.

[Catalyst]

Thanks guys for your help, but there is another little problem. My teacher said that my experiment had to be measurable and that I need to find a way to measure they pressure inside the heated can and the pressure inside the can once its been crushed. Any ideas?

[Catalyst]

come on please help all I need to know is a way to make the pressure measurable and that's it.

[Bluenoise]

Won't the pressure just be the same as the external pressure for before heating and after?

I guess if you used a container with a screw top you could measure the change in volume of the can to determine the drop in pressure caused by the condensation of the steam. And just use Ideal gas law for simplicities sake...

It wouldn't be terribly accurate but it would give you something. I don't think accuracy matters too much in a demonstration.

[Bluenoise]

Um let me elaborate. Use a can with a screw top, after it's been crused place it in a graduated container and open it upside down, since there will still be a slight vacume in the can some water will get pulled in. Carefully screw it back on and measure the volume of water that got taken into the can. Use this to calculate the pressure difference between the crushed can and the external pressure. Subtract this from the external pressure and that gives you the pressure in the can after being crushed.

Then you can use the total change in volume of the can to calculate the pressure change from right as it was cooled till it was opened. Subtract this from your pressure after crushing and you have the pressure once cooled.

 

The pressure in the heated can will just be same as the external pressure.

 

And if you use a pop can without a screw top well then it's an open system and the pressure will pretty much always be the same except for while it's being crushed.

 

By the way I made this up off the top of my head. So if someone who knows better well knows better tell me so and I'll shut up.

[Catalyst]

thanks for that but it's confusing as hell... it would be great if you could just baby step me through this

[Bluenoise]

I'm sorry but I neither have the patients or the will to spend half an hour inventing a procedure. Giving someone suggestions and doing their homework for them are two completely different things.

I hope I don't sound rude, I'm willing to answer any questions you have, but if the only reason you'll pass is because of the work of others well maybe you don't deserve to; redoing the course might be good for you.

[Catalyst]

that's alright blue, is there any other way besides that to calculate the pressure? Maybe using some kind of device?

[Bluenoise]

I'm pretty sure there is, but you'd probably have to ask in the Physics forum. And I think it would be alot harder to setup.

 

Using the ideal gas equation would be by far the easiest way to do this. (though not very accurate since steam is far from ideal)

 

PV = nRT

 

Change in pressure = (n x R x T1 / V1) - (n x R x T2 / V2)

to give an estimate

 

 

has to be the easiest way to do this.