Science Buddies: "Ask an Expert"

Hey expert!

I am doing an experiment on what kind of beans will produce the most gas using a homemade manometer. This was made by putting the beans in a jar, attaching the jar to a u-shaped plastic tube, putting water in the tube, sealing the whole thing off, then measuring how far the water moves upward to get the pressure. After that, I plugged my results into the equation PV=nRT o et the moles of gas produced. The problem is that instead of going upward, the water is going the opposite way. Moles of gas can't dissapear, so I'm stumped. Any ideas?

Thank You,
Danzer135

Hi Danzer135,
Welcome to the Ask an Expert forum. It is difficult to say for sure what is going on with your experiment without seeing it, but here are a few things to consider:
Did the temperature change?
Is your manometer closed to the atmosphere? If so, is it possible there is a leak in your manometer? If it is open to the atmosphere, was there a change in barometric pressure?
Is it really true that gas can't "disappear" as a result of chemical reactions?

If you could post a photo of your apparatus, that would be helpful.

Thanks,
Chris

Hello Danzer135,
Like ChrisG has mentioned, it would be beneficial if we could get a sense of how your apparatus looks like; also, if the manometer is open to the atmosphere, the barometric pressure may be stronger than the pressure being exerted by the gas. If the barometric pressure is greater than the gas pressure from the beans, then this could be one possible explanation for your dilemma. In addition, the beans might not be giving off enough gas. How exactly are you having the beans decompose?