Kevan Mulvaney
Posts: 2
Joined: Sun Nov 11, 2007 10:08 am

How fast does an alks seltzer tablet make gas

Postby Kevan Mulvaney » Sun Nov 11, 2007 10:21 am

got a problem- was able to set up the bottle with the tubing attached to a 60 ml syringe -can see the reation in the bottle but nothing happens in the syringe - waht am i not ding please? :(

Louise
Former Expert
Posts: 921
Joined: Mon Jan 16, 2006 2:17 pm

Re: How fast does an alks seltzer tablet make gas

Postby Louise » Sun Nov 11, 2007 11:21 am

Kevan Mulvaney wrote:got a problem- was able to set up the bottle with the tubing attached to a 60 ml syringe -can see the reation in the bottle but nothing happens in the syringe - waht am i not ding please? :(


Hi Kevan,
It always helps us if you can provide the link to the instructions and as much detail as possible. With out knowing exactly what you are doing, I would guess that the volume of your setup is too large compared to the volume of gas made, so you don't have enough pressure to expand in to the syringe. A plastic bottle and plastic tubing can expand a little anyway, so if you are only making a small amount of gas, it wouldn't show up on the syringe. Also, all connections must be very tight, otherwise the excess gas will leak out.

You can either reduce the size of the system, or you could make more gas by using more tablets in the bottle. To check for leaks, you can put the whole system under water. You can either run with some tablets and see if you see bubbles in the water or slightly squeeze the bottle, and see if the air goes in to the water.

One last thing, you do have a hypothesis, right? What you've posted here is just a measurement. What question are you you trying to answer?

Good luck.

Louise

barretttomlinson
Former Expert
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Joined: Wed Oct 03, 2007 12:24 am

Postby barretttomlinson » Sun Nov 11, 2007 12:44 pm

I am guessing you are doing the Science Fair project posted under the Science Fair ideas in the Chemistry section. The project there proposes two ways of doing the experiment, one using a syringe and the other using a graduated cylinder. I suspect strongly the experiment using the graduated cylinder method will work better. If your experimental apparatus is free of leaks, when the reaction happens making more carbon dioxide two things can happen: the pressure can go up while the volume stays constant or the pressure stays constant and the volume goes up (or a combination of both). For an explanation of this, look up Boyles Law:
http://members.aol.com/profchm/boyle.html

I suspect what may be happening is the plunger of the syringe is hard to move in the syringe barrel, tending to keep the volume constant and causing the pressure to increase. This would mean you would not see the plunger move even though the reaction is happening.

When you do the graduated cylinder version of the experiment the pressure will be held nearly constant, especially if you keep the water levels inside the cylinder at the same level of the as the water level outside the cylinder.

You might be able to quickly convert from syringe method to cylinder method just by pulling the plunger out of the syringe and then using the body of the syringe as a graduated cylinder.

I hope this helps. This is a great experiment!

Kevan Mulvaney
Posts: 2
Joined: Sun Nov 11, 2007 10:08 am

Postby Kevan Mulvaney » Thu Nov 22, 2007 8:36 am

thanks very much - used the graduated cylinder method and it did work! I actually used an inverted baby bottle that had markings

thanks for your help.
moose


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