Help with measuring the amount of air you would breathe

[GinaTy05]

I'm supposed to be conducting an experiment for my chemistry class. Here is the task:

The gas laws are used to determine the pressure of compressed air in a scuba tank. This project will require you to make some basic measurements necessary to calculate the amount of air required to remain underwater for a given time. You will devise a method for measuring the amount of air you would breathe in 30 minutes. Then, using the appropriate gas law, you will calculate the final pressure of a scuba tank holding that much air.

Any help would be much appreciated! Please email me at RTyquiengco@aol.com or reply back on here. Thank you.

[Quarrior]

do a google search on dive planning and air consumption

[H2Andy]

i see three setps to your problem:

1. how much air do you breathe at the surface in 30 minutes. (easy: you
measure how much air you breathe in five minutes and multiply by 6, for example;
an easy way of doing this is to start with a small pony bottle, figure out how much
air you start with, then how much you end up with, and substract)

2. at any given depth, how much faster would you consume that air (and thus how much more air would you need to remain there for 30 minutes)?

3. for the various depths, what would the pressure of the air in the tank be? (i assume in psi, but could be bar).

hope that helps... you should be able to do the rest from your knowledge of gas laws.

[Uncle Pug]

You would need to know:
1. The amount of air you use at the surface.
2. The depth at which you would be breathing from the scuba tank.
3. The initial pressure of the scuba tank.
4. The capacity of the scuba tank.

Make it easy on yourself and assume these values for the above:
1. .5 cubic feet per minute
2. 33' sea water (which equals 1 atmosphere)
3. 3000 psi
4. 80 cubic feet when filled to 3000 psi

Need help stringing this together for the answer?

[H2Andy]

Pug, i think she's supposed to actually measure the amount of air she breathes
at the surface. sounds like a hands-on type thing.

Gina, what grade is this for?

[Uncle Pug]

I always look for the easy way. :D I guess the part about *devise a method for measuring the amount of air you would breath* requires an addition to the list of assumptions.
1. I would breath from a scuba tank at the suface for 6 minutes, note the pressure drop and multiply by 5.
2. I am assuming that my depth would be 33' which is 1 atmosphere... which is an increase in ambient pressure of 100% thus doubling the answer in step 1. (here is where you use the gas law)
3. I would assume that I started with a full tank at 3000 psi and so my final pressure would be 3000 minus the answer from step 2.

Actually, eliminating the conversion between volume and pressure makes it even easier. No access to a scuba tank is needed. Just make the assumption that you used 600 psi at the surface.

[The Kraken]

Well, on one of those days that it's just too crappy to go diving, if there is such a thing, go rent a tank, bring it home, set up your regulator sit down on the sofa, turn on the football game and see how long it take you to breathe the tank down.

Now don't forget to write the time down when you started breathing from the tank.

When you run out of air, divide the amount of air that was in the tank by the number of minutes you breathed before you ran out of air.

This will give you your surface air consumption in cubic feet per minute.

[GinaTy05]

i see three setps to your problem:

1. how much air do you breathe at the surface in 30 minutes. (easy: you
measure how much air you breathe in five minutes and multiply by 6, for example;
an easy way of doing this is to start with a small pony bottle, figure out how much
air you start with, then how much you end up with, and substract)

2. at any given depth, how much faster would you consume that air (and thus how much more air would you need to remain there for 30 minutes)?

3. for the various depths, what would the pressure of the air in the tank be? (i assume in psi, but could be bar).

hope that helps... you should be able to do the rest from your knowledge of gas laws.


Thank you. I think that the bottle method would be perfect.

[GinaTy05]

You would need to know:
1. The amount of air you use at the surface.
2. The depth at which you would be breathing from the scuba tank.
3. The initial pressure of the scuba tank.
4. The capacity of the scuba tank.

Make it easy on yourself and assume these values for the above:
1. .5 cubic feet per minute
2. 33' sea water (which equals 1 atmosphere)
3. 3000 psi
4. 80 cubic feet when filled to 3000 psi

Need help stringing this together for the answer?

LOL, yes, I will need some help.

[GinaTy05]

Pug, i think she's supposed to actually measure the amount of air she breathes
at the surface. sounds like a hands-on type thing.

Gina, what grade is this for?

This is a grade for my chemistry class. This project is basically takes up the whole grading period so I have to do well on it if I want to pass.

[GinaTy05]

I always look for the easy way. :D I guess the part about *devise a method for measuring the amount of air you would breath* requires an addition to the list of assumptions.
1. I would breath from a scuba tank at the suface for 6 minutes, note the pressure drop and multiply by 5.
2. I am assuming that my depth would be 33' which is 1 atmosphere... which is an increase in ambient pressure of 100% thus doubling the answer in step 1. (here is where you use the gas law)
3. I would assume that I started with a full tank at 3000 psi and so my final pressure would be 3000 minus the answer from step 2.

Actually, eliminating the conversion between volume and pressure makes it even easier. No access to a scuba tank is needed. Just make the assumption that you used 600 psi at the surface.

I think I'll just make that assumption, haha. Thank you veyr much!

[TwoBitTxn]

I believe Andy was asking what year in school. 11th grade, 10th grade...?

When you go to breath off the reg, you will need to plug your nose. Humans are inherant nose breathers. Watch TV with a mask on your face. Guaranteed to make people look at you funny.

Good Luck,

TwoBit

[rab]

Gina,
I'm going to assume that you're not a diver and might have misunderstood what a "pony bottle" is. This is a small scuba cylinder/tank that's typically 25% or less the size (capacity) of what a diver would typically use.

I'll also assume that you have access to a large graduated cylinder or beaker and some tubing. If you place the beaker in water, filled and upside down, you can put the end of a short length of tubing under the rim. Measure the volume of several exhalations (normal ones, not blowing up balloon ones!) and get an average. This can be combined with your respiratory rate (breaths per minute) to give your Respiratory Minute Volume. From there, you can use gas laws and scuba cylinder sizes to get your final answer. If you show all of your work and document your experimental methods, you should do fine.

-Rob

[H2Andy]

I believe Andy was asking what year in school. 11th grade, 10th grade...?



Gina:

yes... TwoBitTxn is right... i wanted to know what school year this project
was for.

[GinaTy05]

I believe Andy was asking what year in school. 11th grade, 10th grade...?

When you go to breath off the reg, you will need to plug your nose. Humans are inherant nose breathers. Watch TV with a mask on your face. Guaranteed to make people look at you funny.

Good Luck,

TwoBit

12th grade

[Rick Murchison]

12th grade
Hmmm...
a 12th grade project for a whole course has the possibility of being a much more complex problem than what we normally do in the world of scuba.
Better ask your teacher where the "final pressure" measurement is to be taken. That answer will go a long way to telling us whether he/she wants the simple answer or the complex one.
Rick

[Tobagoman]

Gina,
A couple of things to remember;
If there is going to be a temperature difference between ambient air when you are on the surface and the water at depth you will need to calculate the pressure difference in the tank due to the temperature change (P1V1/T1=P2V2/T2).
Also, remember that for every 33' of salt water depth, you add another atmosphere of pressure. So at 33' you would have 2 atmospheres absolute, 66' you would have 3 ata....
On a rigid container such as a scuba cylinder, the volume remains constant, but as the air leaves the cylinder it is compressed by the ATA's at the depth in question so at 33' (2 ata) you are breathing twice as many air molecules as on the surface, so your consumtion is doubled. It would be trippled at 66'. On top of this, colder water temps will reduce the cylinder pressure.
I am a marine biologist/chemist, if you have any questions you can send me a PM.



I'm supposed to be conducting an experiment for my chemistry class. Here is the task:

The gas laws are used to determine the pressure of compressed air in a scuba tank. This project will require you to make some basic measurements necessary to calculate the amount of air required to remain underwater for a given time. You will devise a method for measuring the amount of air you would breathe in 30 minutes. Then, using the appropriate gas law, you will calculate the final pressure of a scuba tank holding that much air.

Any help would be much appreciated! Please email me at RTyquiengco@aol.com or reply back on here. Thank you.

[Jeddah Aquanaut]

Wow! Where were all of you when I was in high school? ;)




Hmmm...
a 12th grade project for a whole course has the possibility of being a much more complex problem than what we normally do in the world of scuba.
Better ask your teacher where the "final pressure" measurement is to be taken. That answer will go a long way to telling us whether he/she wants the simple answer or the complex one.
Rick