Science Fair - Measuring Ethyelen Gas produced from a fruit?

This is just off the top, but here goes: keep the bag submerged in the water container. Each container is kept at the test temperature, easy, measure the water temp to be sure. The water level is started right up at an overflow pipe. Any gas production will overflow more water, measure that each day. You will need control containers to compare loss from evaporation.

I think you will have to settle for capturing the gas, and assuming that temperature only has effect on ethylene generation and not other gasses such as co2 or N2 or others. Probably not a bad assumption but in your discussion you must preface that it is a basic assumption of the experiement. You will probably get credit for outlining your assumptions.

ethylene can diffuse through ethylene film.

If you go down these links you will find some clues.

http://www.google.ca/#hl=en&source=hp&q=ethylene+%2B%22production+rate%22+%2Bbanana&btnG=Google+Search&meta=&aq=f&oq=ethylene+%2B%22production+rate%22+%2Bbanana&fp=20257e61c65c0f5

http://www.google.ca/#hl=en&safe=off&q=ethylene+%2B%22production+rate%22+%2Bbanana+%2Bppm&meta=&aq=f&oq=ethylene+%2B%22production+rate%22+%2Bbanana+%2Bppm&fp=20257e61c65c0f5

http://www.google.ca/#hl=en&safe=off&q=ethylene+%2B%22production+rate%22+%2Bripening+%2Bppm&meta=&aq=f&oq=ethylene+%2B%22production+rate%22+%2Bripening+%2Bppm&fp=20257e61c65c0f5

Will other gasses also diffuse through the film?

If not, this sounds like a good filtering mechanism for the experiment.

I also know there are different compositions of plastic wrap, one of them being UHMW(ultra high molecular weight polyethylene).Will UHMW also pass ethylene gas exclusively?

I know sea water will absorb CO2, but not certain other gasses (like argon), so perhaps a chemical solution, or series of solutiions that trap everything except ethylene can be arranged, however this is beyond my experience.

EZ Street

diffusion depends on the size of the diffusing material. It also depends on the chemical affinity or similarity.

Polyethylene is more permeable to ethylene than to CO2 or O2.

Helium, the smallest free atom/molecule diffuses the fastest of all. Even H2 is slower because it is larger, being a pair.

These low concentrations of gas, a few PPM, will be hard to measure by displacement methods. I think they use a gas spectrometer or a chromatograph in the lab. There may also be indicator fluids for ethylene?

One can try by connecting balloon to a outlet of gas than pressure and volume of the balloon could be measured. This would let anyone to estimate amount of gas released.

Distinguishing ethylene from CO2 may be difficult. A simple way to measure total gas evolved is get a tall slender bottle and mark graduations on the side as you fill it with water (100 ml, 200 ml,etc) or get a 1 liter graduated cylinder. Put your fruit in another jar. Get some 1/4 inch plastic tubing from the hardware store. Bore a 1/4 inch hole in the lid of the jar with the fruit and stick the hose in it and seal around it with silicone caulk. Now here comes the tricky part. Get a pan half full of water and put 2 blocks (bricks?) in it to set the water bottle on. Put the lid on the full water bottle and turn it upside down. Put the mouth of the water bottle under water and remove the lid. Set the inverted bottle on the blocks (it should still be under water). Run your tubing from the jar for the fruit into the water and stick it inside the water bottle. When you put your fruit in the other jar and secure the lid, gas evolved will go through the tube and bubble into the water jar.As gas bubbles in, it will displace water. Room temperature air will affect the gas volume as the room heats and cools.You might want to figure out a way to secure the water jar so it doesn't tip over, like maybe a ring stand.

If I remember my ancient classes in undergraduate gravimetric analysis, I believe you can pass a stream of air through your reaction vessels and into a scrubber containing a solution of Ca(OH)2, and weigh the dried CaCO3 formed as a measure of the CO2 released, then pass the gas stream through a solution of KMnO4 and weigh the dried MnO2 formed as a measure of the ethylene released. Simple apparatus, only requires a fairly good balance, which most labs should have.

I had forgotten the chemicals involved, but what you describe here sounds a lot like the Orsat apparatus I mentioned. I think this device was used primarily as a flue gas analyzer, and then was adopted for measuring controlled fruit atmospheres. It works by volume rather than weight, however. This was before Bacharach and other electronic instruments came along. Thanks for the reminder!