THINK URBAN GARDENING REDUCES YOUR CARBON FOOTPRINT? What your tomato plants don t want you to know

Transcription

1 THINK URBAN GARDENING REDUCES YOUR CARBON FOOTPRINT? What your tomato plants don t want you to know

2 Four composting jars were set up to measure the amount of CO 2 produced by decomposing tomato plants. Each jar contained a100 ml beaker of 25 ml M NaOH, one contained only NaOH, one contained autoclaved plant matter and two more contained approximately g of plant matter. The plant matter was left to sit for one week and then observations were made. NaOH was preciptated out with 0.5 M Sr (aq) as Na 2 CO 3 and then the solution was titrated with M HCl. From the volume of HCl needed to titrate the solution, the remaining unreacted NaOH was calculated and used to determine the amount of CO 2 produced using the balanced chemical equation: CO 2 + 2NaOH Na 2 CO 3 + H 2 O. It was found via dimensional analysis that an average of ± grams of CO 2 were produced per gram of tomato plant, per day, (~6.4 mg of carbon) which is not significant enough to offset any meaningful amount of CO 2 contribution by other activities.

3 Background There are many factors that affect the amount of carbon dioxide (CO2) in the atmosphere, but by burning the fossil fuels that we use to fuel our homes, our cars and our industrial processes, we increase the amount already present in the atmosphere, which the land and ocean cannot absorb. We now know that this adversely affects the environment by increasing the global warming trend produced by the enhanced greenhouse effect. The negatives associated with global warming are serious: sea level rise, more climate variability, melting glaciers and polar ice caps, species extinction, and many more. It is important not only to understand the anthropogenic causes of release of (CO2), but also the natural causes.

4 Photosynthesis: Nature s carbon cycling mechanism Above ground Below ground nco 2 + mh 2 O Cn (H 2 O)m + no 2 Generic equation for photosynthesis Cn (H 2 O)m + no 2 nco 2 + mh 2 O Generic equation for respiration by microbes, which decompose plants CO 2 + 2NaOH Na 2 CO 3 + H 2 O Balanced chemical equation for precipitation of NaOH with CO 2 1. Sr NO Na + + CO 3 2- SrCO 3 + 2Na(NO 3 ).And with Sr

5 We set up four composting jars, each containing 25 ml of M NaOH, and three of the jars with approximately one gram of dead tomato plant from Dr. Wicht s tomato garden (the jar without plant matter was a control and jar 2 contained autoclaved tomato plant, which served as another control to eliminate any possible bacterial growth). The jars were left for one week to allow time for decomposition The carbonate was precipitated out with strontium and then the NaOH from each jar was titrated with HCl.

6 Experimental design

7 Getting results: A quick introduction to analysis We used dimensional analysis to determine how many grams of CO 2 per gram of tomato plant per day were released by respiration. The molarity of NaOH was calculated for each sample after 7 days: Then, from the molarity, the change in moles was calculated: Then, from the change in moles, the grams of CO 2 consumed were calculated Then, from this information, the number of grams of CO 2 produced per gram of tomato plant per day was calculated:

8 Results:

9 So what does it all mean? Characteristic white fuzz (mold) was observed on all of the tomato plants (yes, even the autoclaved plant), in varying degrees. Average rate of CO 2 formation was g of CO 2 per gram of tomato plant, per day, which is equal to 6.4 mg of pure carbon. Meaning. It would take 69.7 days to decompose 1 gram of plant matter. 6.4 mg/day X 69.7 days = mg/day Therefore, no significant amount of carbon emissions are offset by gardening.

10 Did you know? When you drive Let s suppose that the average fuel efficiency for a car is 25 mpg, and the cautious environmentally conscious consumer drives 6,000 miles in a year (using a fuel comprised of primarily octane) How much carbon do you think is produced? HINT: the balanced chemical equation for complete combustion of octane is: 2C 8 H 18(g) + 25O 2 (g) 16 CO 2 (g) + 18H 2 O (aq) And the density of octane is g/ml. Good luck!!! What is your carbon contribution?

11 And the EPA says If we would like to check these calculations to see if this number makes sense, we can. According to the Environmental Protection Agency (EPA) the average carbon content in 1 US gallon of gasoline is approximately 2,421 g. If someone consumes 240 gallons of gasoline per year, then 240 gallons X 2,421 grams of carbon/gallon = 581,040 grams of carbon produced. These two numbers are fairly close (both are approximations) and therefore this final number is valid.

12 So why is gardening good? Why do we bother with gardening and growing our own vegetables when it doesn t even come close to offsetting our carbon footprint? Reduce trips to the supermarket (so you can lower the amount of carbon you put in the atmosphere by driving) Knowing what s in your food: You grew it, you know what you did and didn t use A sense of accomplishment!