Science Buddies: "Ask an Expert"

Hi! My daughter is in 7th grade advanced science and she is doing her experiment following the biomass energy project listed on this site. We have done a lot of research and in our readings we came across one of the experts on this site advising someone to find out how you could be sure that methane is the gas that is being produced as oppossed to CO2. I have searched for the answer to this question and have not been able to find any information that would explain tests we could do at home. I think this information would really enhance her project. Can anyone help? Thanks!

CO2 is very dense (about 1.5 times as dense\heavy as air). It also does not burn. If CO2 is released in a closed system (say an empty small aquarium) near a candle the CO2 will displace the air and snuff the candle. Methane will easily burn in air, and is lighter than air.

Be VERY careful with this experiment. Methane does burn, but if you get enough methane at once you will have an explosion on your hands. Make sure you and your student are wearing proper safety equipment if you decide to use a candle, and use only a small amount of the collected gas.

I would suggest sniffing the gas produced instead--methane has a distinctive, characteristic smell, whereas CO2 is odorless.

Hi,

This is a really great project.

https://www.sciencebuddies.org/science- ... p027.shtml

The density of the gases that dason29 mentioned is the key to verifying what type of gas has been produced. I have not tried the following, but I think it would work: Since you will be filling a balloon with the gas produced in the soda bottle with ruminant bacteria and biomass, you can tie off the balloon after it is filled with gas and gently roll it off a table and measure the time that it takes to drop to the floor. A balloon with pure methane would float in air; a balloon with pure carbon dioxide would fall very quickly. I think that the balloon will actually contain a mixture of methane and carbon dioxide.

Donna Hardy

WOW! These all all great responses and I am so appreciative for all of ya'lls time. We will definately try these suggestions.

Here is an update on the project....It is day 3 and we have noticed something very interesting. Most of the balloons, particularly the cow manure + banana, look like all the air has been sucked out of the balloons. They are kind of collapsed. I'm thinking this is a good sign because the bacteria are ridding the bottles of all O2 so that the anaerobic methanogens are able to grow and begin producing gas??? I'm keeping my fingers crossed that we will see some production in a couple of days. We have been careful not to move the bottles and we live in Florida so the temp hasn't been a problem. It's getting exciting!

Donna,

If we did this test, I'm thinking we would have to test against a balloon that is blown up (this would be CO2 right?)....Since it is not the core of the project, could we just do a few tests against the regular balloons? Would that be sufficient eveidence?

Also, to all that responded, how do we list you as a resource in the bibliography. Do we just put science buddies or do we name you individually. Thanks!

Hi,

Are your balloons filling with gas yet? It sounds like the barometric pressure changed and this caused the balloons to collapse temporarily. However, your report is good because it confirms that the bottles are sealed and conditions will soon be ideal for growing the anaerobic bacteria. If you need a control for the balloon drop experiment, you could use a bicycle tire pump to fill the balloon with air (about 80 nitrogen gas, 20% oxygen gas, and since you are in Florida, some water vapor). If you blow up the balloon yourself it would contain some extra carbon dioxide as well, but not 100% carbon dioxide. However, it would be a good reference point that would allow you to compare the density of the gas in the test balloons.

If your balloons are not filling up with gas yet, and if it's been more than 7-8 days since you started, you may need to start over with really fresh cow manure.

It's great you are thinking about citing your resources. You can acknowledge the Science Buddies website (www.sciencebuddies.com) and the name of the individual experts who have provided specific advice for your project. You should also include other references on your topic. The Science Fair judges will be interested in knowing that you understand the sceince behind your project.

Please do let us know about your results.


can Donna Hardy

It is Day 6 now and we do have a little bit of gas in all of the balloons with more being in the trials with mashed banana. I am starting to get concerned because I thought there would be more. The manure was a couple of hours old so I do worry about that. We're kinda running out of time, though. The project is due Oct 31st so I'm thinking that we will just go with whatever data we have at the end and then explain, if needed, the reasons the results may not be as expected. Thanks so much for everything.

Hi,

If you are only on on day 6, then you should see significant gas production within the next 2-3 days. The manure was fresh enough, but anaerobic bacteria always seem to be damaged by exposure to oxygen during handling and it seems to take them a while to recover and start growing. I think you will have some results to report, but you are right, since you are running out of time, it's perfectly fine to report the results you obtain and then explain them. You can spend the time you have left in writing up your board and explaining the science behind your project.

Donna Hardy